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Phenoptosis, behavior evolved for good of species?

Phenoptosis, behavior evolved for good of species?


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I was reading this and felt like the argument is being made that organisms die for the good of species. Isn't this nonsense?

This especially bugged me:

"'Age-induced, soft, or slow phenoptosis'" is the slow deterioration and death of an organism due to accumulated stresses over long periods of time. In short, it has been proposed that aging, heart disease, cancer, and other age related ailments are means of phenoptosis. "'Death caused by aging clears the population of ancestors and frees space for progeny carrying new useful traits.'"

Per the selfish nature of genes, it might be okay if it was only your offspring you are dying for, but even that only when you know you can't reproduce further. And the above argument says that old age death is exactly that.


I don't really have an opinion on whether or not this is the main or even a reason for the evolution of senescence and death, but it is certainly not nonsense.

Death can indeed be good for a species. Diversity is always good and the death of the elders allows phenotypes that have been selected for more recently to take hold in the gene pool. If the young need to compete with the old, this will make it harder for them to grow and reproduce. In situations with a limited food supply, having to support old individuals who can no longer forage/hunt for themselves will be a strain on the species/society/pod or whatever it is we are looking at.

Therefore, genotypes that encourage the death of elders who are past the age of reproduction could be selected for. This does not contravene the selfish gene hypothesis at all, these individuals have already reproduced, the selfish gene no longer 'cares' about them. The main idea of the selfish gene hypothesis is that the genes themselves 'want' to be passed on, not that the genes 'want' to save themselves. Once their host has reproduced, they loose interest so to speak.

The selfish gene theory is just a conceptual tool, it should not be taken literally. It does not suggest that genes are actually selfish or in charge of their own evolution in any way. It is just a useful approach to take when studying evolution and was instrumental in our understanding that the gene (the nucleotide actually) and not the individual is the smallest unit of selection.

Anyway, in the strictest sense, the statement in your question is absolutely compatible with the selfish gene hypothesis. If you can no longer pass your genes along, you are useless and just a drain on the species, why should you keep living?


E. O. Wilson

Edward Osborne Wilson (born June 10, 1929), usually cited as E. O. Wilson, is an American biologist, naturalist, and writer. Wilson is an influential biologist [3] [4] [5] who on numerous occasions has been given the nicknames "The New Darwin", "Darwin's natural heir" or "The Darwin of the 21st century". [6] [7] [8] His biological specialty is myrmecology, the study of ants, on which he has been called the world's leading expert. [9] [10] [11]

    (1967) (1979) (1979) (1984) (1990) (1991) (1993) (1994) (2000)
  • King Faisal Prize (2000) (2001) (2001) in Ecology and Conservation Biology (2010) (2012) (2014) [1]

Wilson has been called "the father of sociobiology" and "the father of biodiversity" [12] for his environmental advocacy, and his secular-humanist and deist ideas pertaining to religious and ethical matters. [13] Among his greatest contributions to ecological theory is the theory of island biogeography, which he developed in collaboration with the mathematical ecologist Robert MacArthur. This theory served as the foundation of the field of conservation area design, as well as the unified neutral theory of biodiversity of Stephen Hubbell.

Wilson is [update] the Pellegrino University Research Professor, Emeritus in Entomology for the Department of Organismic and Evolutionary Biology at Harvard University, a lecturer at Duke University, [14] and a Fellow of the Committee for Skeptical Inquiry. The Royal Swedish Academy, which awards the Nobel Prize, awarded Dr. Wilson the Crafoord Prize, an award designed to cover areas not covered by Nobel Prizes (biology, oceanography, mathematics, astronomy etc.). He is a Humanist Laureate of the International Academy of Humanism. [15] [16] He is a two-time winner of the Pulitzer Prize for General Nonfiction (for On Human Nature in 1979, and The Ants in 1991) and a New York Times bestselling author for The Social Conquest of Earth, [17] Letters to a Young Scientist, [17] [18] and The Meaning of Human Existence.

He has written more than 30 books and published more than 430 scientific papers, some of them being the most cited in history and the cover of such important scientific journals as Nature or Science. His articles "Character displacement" published in 1956 in co-authorship with William Brown Jr., "The Theory of Island Biogeography" prepared together with Robert H. MacArthur in 1967, "Experimental zoogeography of islands: the colonization of empty islands" prepared in 1969 together D. S. Simberloff and his books "The Insect Societies" and "Sociobiology: The New Synthesis" were honored with the Science Citation Classic award, the most important award that identifies the most cited works or works that are references on the field. [19]

He has also received more than 150 prestigious awards and medals around the world, as well as more than 40 honorary doctorates. [20] [19] He is an honorary member of more than 30 world renowned and prestigious organizations, academies and institutions. He has been invited to give lectures at more than 100 universities and institutions around the world. Two animal species have been scientifically named in his honor. [21] [22]

In 1995 he was named one of the 25 most influential personalities in America by Time magazine, and in 1996 an international survey ranked him as one of the 100 most influential scientists in history. In 2000, Time and Audubon magazines named him one of the 100 Leading Environmentalists of the Century. In 2005, Foreign Policy named him one of the 100 most important intellectuals in the world. [20] In 2008 he was elected one of the 100 most important scientists in history by the Britannica Guide. [23] In the following years and up to the present he has been included in numerous similar lists such as the list "The 50 most influential scientists in the world today" prepared by TheBestSchools. [24]


Preamble: declaration of the holistic viewpoint

The Universe consists of discrete entities: elementary particles, atoms, molecules, planets, stars, galaxies. That is there are a limited number of configurations of matter that are fairly stable and lasting, the intermediate ones being volatile. The Universe is structuralized. It means that it is far from thermodynamic equilibrium it contains information it exists. The existence of the Universe depends on the mutual affinity of its constituents, their ability to interact with each other, thus resisting the general aspiration for evenness. Initially, the Darwinian natural selection, acting by the accumulation of tiny heritable changes, was supposed to produce an even continuum of the living beings. This expectation was never corroborated. The biological world follows the same global principle: organisms, populations, species, ecosystems are discrete, relatively stable entities, the intermediate configurations being volatile. Biological evolution cannot retain everything that randomly emerges. The stability of the biotic entities is determined not merely by their physical durability but by their expedient behavior especially. They are organizations with the function of survival. The Universe evolves via the interaction and cooperation of the entities, whence its complexity and hierarchical structure come from. The major transitions in biological evolution (macromolecular replicator → prokaryotic cell → eukaryotic cell → multicellular organism → biological species) are also the steps of cooperation [1]. Though a complex entity consists of the other simpler ones, it is not just an aggregate of the included entities. It is a qualitatively new form of existence it is an organization of a higher rank. Hierarchy in biology doesn't mean just complexity or heterogeneity. It implies a functional predestination of their parts for the sake of the whole. Survival of the parts crucially depends on survival of the whole. Hence, constituent entities are to be included into the higher entities only in an appropriately transformed configuration. The operating principles of the organization of the higher rank are not necessarily related to or derivable from the properties of the parts or to their internal operating principles. That is the principles organizing an upper rank are novelties. They are not necessarily predictable from the rank below. On the other hand, the organizing restrictions of the living entities, being emerged as a frozen chance, cannot be deduced from any general principle or law. They can be understood only retrospectively, in the context of their history. The above statements imply that the evolution of a higher entity cannot be adequately presented as self-sufficing evolution of its constituents. The prosperity of the whole is the vector of selection for the constituent entities.


2. Kin Selection and Inclusive Fitness

The basic idea of kin selection is simple. Imagine a gene which causes its bearer to behave altruistically towards other organisms, e.g. by sharing food with them. Organisms without the gene are selfish&mdashthey keep all their food for themselves, and sometimes get handouts from the altruists. Clearly the altruists will be at a fitness disadvantage, so we should expect the altruistic gene to be eliminated from the population. However, suppose that altruists are discriminating in who they share food with. They do not share with just anybody, but only with their relatives. This immediately changes things. For relatives are genetically similar&mdashthey share genes with one another. So when an organism carrying the altruistic gene shares his food, there is a certain probability that the recipients of the food will also carry copies of that gene. (How probable depends on how closely related they are.) This means that the altruistic gene can in principle spread by natural selection. The gene causes an organism to behave in a way which reduces its own fitness but boosts the fitness of its relatives&mdashwho have a greater than average chance of carrying the gene themselves. So the overall effect of the behaviour may be to increase the number of copies of the altruistic gene found in the next generation, and thus the incidence of the altruistic behaviour itself.

Though this argument was hinted at by Haldane in the 1930s, and to a lesser extent by Darwin in his discussion of sterile insect castes in The Origin of Species, it was first made explicit by William Hamilton (1964) in a pair of seminal papers. Hamilton demonstrated rigorously that an altruistic gene will be favoured by natural selection when a certain condition, known as Hamilton's rule, is satisfied. In its simplest version, the rule states that b > c/r, where c is the cost incurred by the altruist (the donor), b is the benefit received by the recipients of the altruism, and r is the co-efficient of relationship between donor and recipient. The costs and benefits are measured in terms of reproductive fitness. The co-efficient of relationship depends on the genealogical relation between donor and recipient&mdashit is defined as the probability that donor and recipient share genes at a given locus that are &lsquoidentical by descent&rsquo. (Two genes are identical by descent if they are copies of a single gene in a shared ancestor.) In a sexually reproducing diploid species, the value of r for full siblings is ½, for parents and offspring ½, for grandparents and grandoffspring ¼, for full cousins 1/8, and so-on. The higher the value of r, the greater the probability that the recipient of the altruistic behaviour will also possess the gene for altruism. So what Hamilton's rule tells us is that a gene for altruism can spread by natural selection, so long as the cost incurred by the altruist is offset by a sufficient amount of benefit to sufficiently closed related relatives. The proof of Hamilton's rule relies on certain non-trivial assumptions see Frank 1998, Grafen 1985, 2006, Queller 1992a, 1992b, Boyd and McIlreath 2006 and Birch forthcoming for details.

Though Hamilton himself did not use the term, his idea quickly became known as &lsquokin selection&rsquo, for obvious reasons. Kin selection theory predicts that animals are more likely to behave altruistically towards their relatives than towards unrelated members of their species. Moreover, it predicts that the degree of altruism will be greater, the closer the relationship. In the years since Hamilton's theory was devised, these predictions have been amply confirmed by empirical work. For example, in various bird species, it has been found that &lsquohelper&rsquo birds are much more likely to help relatives raise their young, than they are to help unrelated breeding pairs. Similarly, studies of Japanese macaques have shown that altruistic actions, such as defending others from attack, tend to be preferentially directed towards close kin. In most social insect species, a peculiarity of the genetic system known as &lsquohaplodiploidy&rsquo means that females on average share more genes with their sisters than with their own offspring. So a female may well be able to get more genes into the next generation by helping the queen reproduce, hence increasing the number of sisters she will have, rather than by having offspring of her own. Kin selection theory therefore provides a neat explanation of how sterility in the social insects may have evolved by Darwinian means. (Note, however, that the precise significance of haplodiploidy for the evolution of worker sterility is a controversial question see Maynard Smith and Szathmary 1995 ch.16, Gardner, Alpedrinha and West 2012.)

Kin selection theory is often presented as a triumph of the &lsquogene's-eye view of evolution&rsquo, which sees organic evolution as the result of competition among genes for increased representation in the gene-pool, and individual organisms as mere &lsquovehicles&rsquo that genes have constructed to aid their propagation (Dawkins 1976, 1982). The gene's eye-view is certainly the easiest way of understanding kin selection, and was employed by Hamilton himself in his 1964 papers. Altruism seems anomalous from the individual organism's point of view, but from the gene's point of view it makes good sense. A gene wants to maximize the number of copies of itself that are found in the next generation one way of doing that is to cause its host organism to behave altruistically towards other bearers of the gene, so long as the costs and benefits satisfy the Hamilton inequality. But interestingly, Hamilton showed that kin selection can also be understood from the organism's point of view. Though an altruistic behaviour which spreads by kin selection reduces the organism's personal fitness (by definition), it increases what Hamilton called the organism's inclusive fitness. An organism's inclusive fitness is defined as its personal fitness, plus the sum of its weighted effects on the fitness of every other organism in the population, the weights determined by the coefficient of relationship r. Given this definition, natural selection will act to maximise the inclusive fitness of individuals in the population (Grafen 2006). Instead of thinking in terms of selfish genes trying to maximize their future representation in the gene-pool, we can think in terms of organisms trying to maximize their inclusive fitness. Most people find the &lsquogene's eye&rsquo approach to kin selection heuristically simpler than the inclusive fitness approach, but mathematically they are in fact equivalent (Michod 1982, Frank 1998, Boyd and McIlreath 2006, Grafen 2006).

Contrary to what is sometimes thought, kin selection does not require that animals must have the ability to discriminate relatives from non-relatives, less still to calculate coefficients of relationship. Many animals can in fact recognize their kin, often by smell, but kin selection can operate in the absence of such an ability. Hamilton's inequality can be satisfied so long as an animal behaves altruistically towards other animals that are in fact its relatives. The animal might achieve this by having the ability to tell relatives from non-relatives, but this is not the only possibility. An alternative is to use some proximal indicator of kinship. For example, if an animal behaves altruistically towards those in its immediate vicinity, then the recipients of the altruism are likely to be relatives, given that relatives tend to live near each other. No ability to recognize kin is presupposed. Cuckoos exploit precisely this fact, free-riding on the innate tendency of birds to care for the young in their nests.

Another popular misconception is that kin selection theory is committed to &lsquogenetic determinism&rsquo, the idea that genes rigidly determine or control behaviour. Though some sociobiologists have made incautious remarks to this effect, evolutionary theories of behaviour, including kin selection, are not committed to it. So long as the behaviours in question have a genetical component, i.e. are influenced to some extent by one or more genetic factor, then the theories can apply. When Hamilton (1964) talks about a gene which &lsquocauses&rsquo altruism, this is really shorthand for a gene which increases the probability that its bearer will behave altruistically, to some degree. This is much weaker than saying that the behaviour is genetically &lsquodetermined&rsquo, and is quite compatible with the existence of strong environmental influences on the behaviour's expression. Kin selection theory does not deny the truism that all traits are affected by both genes and environment. Nor does it deny that many interesting animal behaviours are transmitted through non-genetical means, such as imitation and social learning (Avital and Jablonka 2000).

The importance of kinship for the evolution of altruism is very widely accepted today, on both theoretical and empirical grounds. However, kinship is really only a way of ensuring that altruists and recipients both carry copies of the altruistic gene, which is the fundamental requirement. If altruism is to evolve, it must be the case that the recipients of altruistic actions have a greater than average probability of being altruists themselves. Kin-directed altruism is the most obvious way of satisfying this condition, but there are other possibilities too (Hamilton 1975, Sober and Wilson 1998, Bowles and Gintis 2011, Gardner and West 2011). For example, if the gene that causes altruism also causes animals to favour a particular feeding ground (for whatever reason), then the required correlation between donor and recipient may be generated. It is this correlation, however brought about, that is necessary for altruism to evolve. This point was noted by Hamilton himself in the 1970s: he stressed that the coefficient of relationship of his 1964 papers should really be replaced with a more general correlation coefficient, which reflects the probability that altruist and recipient share genes, whether because of kinship or not (Hamilton 1970, 1972, 1975). This point is theoretically important, and has not always been recognized but in practice, kinship remains the most important source of statistical associations between altruists and recipients (Maynard Smith 1998, Okasha 2002, West et al. 2007).

2.1 A Simple Illustration: the Prisoner's dilemma

The fact that correlation between donor and recipient is the key to the evolution of altruism can be illustrated via a simple &lsquoone shot&rsquo Prisoner's dilemma game. Consider a large population of organisms who engage in a social interaction in pairs the interaction affects their biological fitness. Organisms are of two types: selfish (S) and altruistic (A). The latter engage in pro-social behaviour, thus benefiting their partner but at a cost to themselves the former do not. So in a mixed (S,A) pair, the selfish organism does better&mdashhe benefits from his partner's altruism without incurring any cost. However, (A,A) pairs do better than (S,S) pairs&mdashfor the former work as a co-operative unit, while the latter do not. The interaction thus has the form of a one-shot Prisoner's dilemma, familiar from game theory. Illustrative payoff values to each &lsquoplayer&rsquo, i.e., each partner in the interaction, measured in units of biological fitness, are shown in the matrix below.

Player 2
Altruist Selfish
Player 1 Altruist 11,11 0,20
Selfish 20,0 5,5
Payoffs for (Player 1, Player 2) in units of reproductive fitness

The question we are interested in is: which type will be favoured by selection? To make the analysis tractable, we make two simplifying assumptions: that reproduction is asexual, and that type is perfectly inherited, i.e., selfish (altruistic) organisms give rise to selfish (altruistic) offspring. Modulo these assumptions, the evolutionary dynamics can be determined very easily, simply by seeing whether the S or the A type has higher fitness, in the overall population. The fitness of the S type, W(S), is the weighted average of the payoff to an S when partnered with an S and the payoff to an S when partnered with an A, where the weights are determined by the probability of having the partner in question. Therefore,

(The conditional probabilities in the above expression should be read as the probability of having a selfish (altruistic) partner, given that one is selfish oneself.)

Similarly, the fitness of the A type is:

From these expressions for the fitnesses of the two types of organism, we can immediately deduce that the altruistic type will only be favoured by selection if there is a statistical correlation between partners, i.e., if altruists have greater than random chance of being paired with other altruists, and similarly for selfish types. For suppose there is no such correlation&mdashas would be the case if the pairs were formed by random sampling from the population. Then, the probability of having a selfish partner would be the same for both S and A types, i.e., P(S partner/S) = P(S partner/A). Similarly, P(A partner/S) = P(A partner/A). From these probabilistic equalities, it follows immediately that W(S) is greater than W(A), as can be seen from the expressions for W(S) and W(A) above so the selfish type will be favoured by natural selection, and will increase in frequency every generation until all the altruists are eliminated from the population. Therefore, in the absence of correlation between partners, selfishness must win out (cf. Skyrms 1996). This confirms the point noted in section 2&mdashthat altruism can only evolve if there is a statistical tendency for the beneficiaries of altruistic actions to be altruists themselves.

If the correlation between partners is sufficiently strong, in this simple model, then it is possible for the condition W(A) > W(S) to be satisfied, and thus for altruism to evolve. The easiest way to see this is to suppose that the correlation is perfect, i.e., selfish types are always paired with other selfish types, and ditto for altruists, so P(S partner/S) = P(A partner/A) = 1. This assumption implies that W(A)=11 and W(S)=5, so altruism evolves. With intermediate degrees of correlation, it is also possible for the condition W(S) > W(A) to be satisfied, given the particular choice of payoff values in the model above.

This simple model also highlights the point made previously, that donor-recipient correlation, rather than genetic relatedness, is the key to the evolution of altruism. What is needed for altruism to evolve, in the model above, is for the probability of having a partner of the same type as oneself to be sufficiently larger than the probability of having a partner of opposite type this ensures that the recipients of altruism have a greater than random chance of being fellow altruists, i.e., donor-recipient correlation. Whether this correlation arises because partners tend to be relatives, or because altruists are able to seek out other altruists and choose them as partners, or for some other reason, makes no difference to the evolutionary dynamics, at least in this simple example.


Three fundamental aspects of emotions

The modem era of emotion research probably started when it became obvious that emotions are not just �lings” or mental states, but are accompanied by physiological and behavioral changes that are an integral part of them. This has progressively led to today's view of emotions being experienced or expressed at three different, but closely interrelated levels: the mental or psychological level, the (neuro)physiological level, and the behavioral level. These three complementary aspects are present in even the most basic emotions, such as fear.

A detailed account of the many “theories of emotion” is beyond the scope of this review. However, a brief historical survey of the more biologically oriented ones may help to set some important conceptual issues. 3-8

One of the main questions addressed by earlier scientific theories of emotions was whether physiological changes precede the emotional experience, or if they are only a consequence of it. For James (1884) and Lange (1885), “[. ] the bodily changes follow directly the perception of the existing fact, and [. ] our feelings of the same changes as they occur IS the emotion.” In other words, according to the James-Lange theory of emotions, stimuli reaching the cerebral cortex induce visceral changes, which are then perceived as emotion. Cannon and Bard (1915-1932) criticized this theory and proposed that the neurophysiological aspects of emotions are subcortical and involve the thalamus. 9 Stimuli from the environment activate the thalamus, which relays information to the cortex and viscera, and back again to the cortex to generate the 𠇎motional state.” Watson, the father of behaviorism, was also very critical of what he called the “introverted viewpoint” of James' theory. He considered that there were only three types of unlearned emotional responses, which he called �r,” “rage,” and “love” for convenience, although he wanted to “[. ] strip them out of all their old connotations.” 10 These three emotional responses can be elicited by three sets of specific stimuli. Thus, a sudden noise or loss of physical support can induce an innate fear reaction, and restraint of bodily movements triggers rage. He also mentioned the fact that these emotional responses can be conditioned and that, although these reactions are usually accompanied by specific behaviors, “[. ] visceral and glandular factors predominate.” Papez's (1937) theory of emotions also had a physiological basis. For him, connections between the cerebral hemispheres and the hypothalamus, and between the cerebral hemispheres and the dorsal thalamus mediate emotions. He held the view that emotion implies behavior (expression) and feeling (experience, subjective aspects). Expression depends on the hypothalamus, and experience on the cortex. Although the 𠇌ircuit of Papez” is still presented as “the emotional brain” in some handbooks, it is clear that many details of his original theory are now outdated. More recently, Schachter (1975) emphasized the importance of cognitive processes: bodily states are interpreted in a cognitive context and are modulated by experience. He also showed that the visceral response appears to be a necessary, although not sufficient, condition for the occurrence of emotion.

The view that there is a limited set of emotions (eg, fear, anger, etc) with specific neurophysiological and neuroanatomical substrates that can be considered as �sic” and serve as the primitive building blocks from which the other, more complex emotions are built, was challenged as late as 1990. 11 However, Ekman has convincingly argued that there is now enough evidence of universals in expression and in physiology to suggest a biological basis for these elementary emotions. 12 Panksepp added to these arguments by stating that “genetically dictated brain systems that mediate affective-emotional processes do exist, even though there are bound to be semantic ambiguities in how we speak about these systems.” 13


Phenoptosis, behavior evolved for good of species? - Biology

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Through all of the anxiety and heightened concerns we have heard, we have clearly seen our campus community embrace the prevention and precautionary measures to help us all fight the spread of COVID-19 together.

To limit the spread of COVID-19, UCLA enacted the following changes effective March 18, 2020:

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Evolutionary theory and psychology

In commemoration of the 200th anniversary of Charles Darwin’s birth and the 150th anniversary of the publication of his seminal work On the Origin of Species, this edition of Psychological Science Agenda includes a special section on evolutionary theory and psychology. Scientists and philosophers were invited to submit personal reflections on the significance and influence of Darwin’s theory and of current views of evolution within contemporary psychology. PSA thanks the authors for their provocative contributions.

An Open Letter to Comparative Psychologists
By Daniel J. Povinelli, Derek C. Penn, and Keith J. Holyoak

Darwin’s Influence on Modern Psychological Science
By David M. Buss

David M. Buss is Professor of Psychology at the University of Texas at Austin.


At the end of his classic treatise in 1859, On the Origin of Species, Darwin envisioned that in the distant future, the field of psychology would be based on a new foundation—that of evolutionary theory. A century and a half later, it’s clear that his vision proved prescient (Buss, 2009).

Evolutionary psychology is not a distinct branch of psychology, but rather a theoretical lens that is currently informing all branches of psychology. It is based on a series of logically consistent and well-confirmed premises: (1) that evolutionary processes have sculpted not merely the body, but also the brain, the psychological mechanisms it houses, and the behavior it produces (2) many of those mechanisms are best conceptualized as psychological adaptations designed to solve problems that historically contributed to survival and reproduction, broadly conceived (3) psychological adaptations, along with byproducts of those adaptations, are activated in modern environments that differ in some important ways from ancestral environments (4) critically, the notion that psychological mechanisms have adaptive functions is a necessary, not an optional, ingredient for a comprehensive psychological science.

Darwin provided two key theories that guide much of modern psychological research—natural selection and sexual selection. These theories have great heuristic value, guiding psychologists to classes of adaptive problems linked with survival (e.g., threats from other species such as snakes and spiders threats from other humans) and reproduction (e.g., mate selection, sexual rivalry, adaptations to ovulation). Advances in modern evolutionary theory heralded by inclusive fitness theory and the “gene’s-eye” perspective guide researchers to phenomena Darwin could not have envisioned, such as inherent and predictable forms of within-family conflict and sexual conflict between males and females.

Over the past decade, evolutionary psychology has increasingly informed each sub-discipline within psychology. In perception and sensation, it has led to the discovery of phenomena such as the auditory looming bias and the visual descent illusion. In cognitive psychology, based on a fusion of signal detection theory and the asymmetric evolutionary costs of cognitive errors, it has led to error management theory and the discovery of functional cognitive biases that are, strange as it may seem, “designed” to err in adaptive ways. Evolutionary social psychology has produced a wealth of discoveries, ranging from adaptations for altruism to the dark sides of social conflict. Evolutionary developmental psychology has explored the ways in which critical ontogentic events, such as father absence versus father presence, influence the subsequent development of sexual strategies.

Evolutionary clinical psychology provides a non-arbitrary definition of psychological disorder--when an evolved mechanism fails to function as it was designed to function. It also sheds light on common afflictions such as depression, anxiety disorders, eating disorders, and sexual disorders. And it provides a framework for examining how mismatches between ancestral and modern environments can create psychological disorders. Personality psychology, historically refractory to evolutionary analysis, is finally beginning to discover adaptive individual differences.

Hybrid disciplines too make use of the tools of evolutionary psychology. Cognitive and social neuroscientists, for example, use modern technologies such as fMRI to test hypotheses about social exclusion adaptations, emotions such as sexual jealousy, and kin recognition mechanisms.

More generally, evolutionary psychology breaks down the barriers between the traditional sub-disciplines of psychology. A proper description of psychological adaptations must include identifying perceptual input, cognitive processing, and developmental emergence. Many mechanisms evolved to solve social adaptive problems, such as when social anxiety functions to motivate behavior that prevents an individual from losing status within a group. And all adaptations can malfunction, as when social anxiety becomes paralyzing rather than functional, making clinical psychology relevant. The key point is that organizing psychology around adaptive problems and evolved psychological solutions, rather than around the somewhat arbitrary sub-fields such as cognitive, social, and developmental, dissolves historically restrictive branch boundaries. Evolutionary psychology provides a metatheory for psychological science that unites these fields, and justifies why the seemingly disparate branches of psychology truly belong within the covers of introductory psychology books and within the same departments of psychology.

Buss, D. M. (2009). The great struggles of life: Darwin and the emergence of evolutionary psychology. American Psychologist, 64, 140-148.

Evolutionary Psychology and the Evolution of Psychology
By Daniel J. Kruger

Daniel Kruger is Research Assistant Professor at the Prevention Research Center of Michigan, in the School of Public Health at the University of Michigan.


The framework of evolutionary theory will be increasingly adopted as the foundation for a cumulative understanding of psychological science. As the unifying theory of the life sciences, evolution by natural and sexual selection offers an unparalleled ability to integrate currently disparate research areas (Wilson, 1998), creating a powerful framework for understanding the complex patterns of causality in psychological and behavioral phenomena. The evolutionary perspective will grow from its perceived status as a special interest area into an organizing principle that pervades every corner of every field, as well as serve as a bridge across levels of analysis.

The incorporation of evolutionary theory into psychology has waxed and waned in the 150 years since Darwin (1859) predicted that the field would be based on a new foundation. There are many notable examples of psychological theories with evolutionary bases, such as Bowlby’s (1969) model of attachment, yet these are often isolated examples. In the last three decades, the evolutionary perspective has been reinvigorated with considerable theoretical advances and a continually growing array of empirical studies.

Claims for such dramatic advancements on currently held beliefs likely evoke skepticism. The massive empirical evidence accumulating for the influence of evolutionary selection pressures on psychological mechanisms will convince objective observers. It is important to note that evolutionary explanations will not necessarily replace the current models for specific psychological and behavioral phenomena, but rather integrate the “how” with the “why.” It may help to recognize that evolutionary psychology is not monolithic there are multiple levels of theory from basic principles to specific phenomena and multiple competing explanatory theories. Disagreements occur even between those considered the founders of the modern field. For example, some believe there are psychological adaptations facilitating homicide for strategic ends (Buss, 2005) whereas others believe that homicide is the product of adaptations for sub-lethal motivations such as competition combined with lethal modern technology (Daly & Wilson, 1988).

It may also help to distinguish modern evolutionary psychology from the selective breeding programs in previous eras of human history. There is no teleology in evolution no person or people are more highly evolved than any other persons or peoples. Everyone alive today is descended from a long, long line of successful ancestors. Yet there may be individual and group differences in psychological domains that are partially a result of differential selection pressures on ancestral populations. Humans have colonized nearly every land area on the surface of the earth, and each of these diverse ecologies could shape our psychological design. Efforts to advance human welfare may benefit from this recognition, as well as the understanding that genes are not the script for a pre-ordained destiny. Everything about us as individuals is a product of complex interactions between our genetic instructions and aspects of the environments in which they are expressed.

By providing the broader context in which research results may be interpreted, researchers across fields will facilitate the integration of a larger body of scientific knowledge. The evolution of psychology will facilitate its recognition and integration as science.

Bowlby, J. (1969). Attachment and loss, Volume. 1. New York: Basic Books.

Buss, D. M. (2005). The Murderer Next Door: Why the Mind is Designed to Kill. New York: Penguin Press.

Daly, M., & Wilson, M. (1988). Homicide. New York: Alidine de Gruyter.

Darwin, C. (1859). On the Origin of Species by Means of Natural Selection. London: John Murray.

Wilson, E.O. (1998). Consilience: The Unity of Knowledge. New York: Alfred A. Knopf.

Darwinizing the Social Sciences
By Robert Kurzban

Robert Kurzban is Associate Professor in the Department of Psychology at the University of Pennsylvania.


There is only one known cause of the complex functional organization of matter that characterizes the biological world: evolution by natural selection. Because scientists do not typically ignore the central causal process that gives rise to the object of their study, it makes sense that 150 years after The Origin of Species, scientific research investigating the physiology or behavior of any of the roughly 1.5 million species on Earth requires graduate training in biology, in particular instruction in the theory of evolution by natural selection, a fact which stands as a tribute to Darwin’s legacy. Scholarship on each of the world’s species is motivated by hypotheses of evolved function, which in turn guides research on proximate mechanisms.

This is true for every single species on the planet with one exception: Homo sapiens.

Students who wish to study humans – psychologists, political scientists, economists, sociologists and other social scientists – are not required to take a single course in biology, and, with few exceptions, they do not. This puts much of the social sciences in the position of trying to explain human psychology without the tools of Darwinism, a circumstance akin to trying do chemistry while keeping studiously ignorant of the causal foundations of the discipline: atoms, molecules, the periodic table, and the basic forces that govern matter.

This leads to embarrassing mistakes. Biologists would never think that an explanation for complex behaviors such as dam-building in beavers would either begin or end with reference to constructs such as “protecting self-esteem,” “salience,” or “maximizing utility,” yet “explanations” of precisely this sort are pervasive in the social sciences. Biologists understand that explanations owe a Darwinian debt: evolved mechanisms have biological functions, and these must, eventually, be explicated. However, not only are explanations that begin with a theory of evolved function still rare in the social sciences, but such explanations, perversely, frequently attract scorn, ridicule, and blind incomprehension.

This situation can be remedied. I offer two suggestions. First, graduate training in all of the social sciences should require at least one class in evolutionary biology. Students entering the field should be armed with the tools that have been so productive in explaining and predicting the behavior of every other species. Psychology can lead the way in this by acting quickly. Second, editors should begin requiring that papers include an explicit hypothesis about the evolved function of the mechanisms investigated in the manuscript. Form follows function in biology, and hypotheses about the form psychological mechanisms take – how they work – should always be informed by hypotheses about function – what they’re designed to do.

The continued stubborn resistance of psychologists to learn the ideas that integrate their discipline with the natural sciences will be viewed unfavorably by posterity. Change has been glacial, leaving psychology to be condemned, as Max Planck is frequently quoted as having said of science, “to advance one funeral at a time.” So, one way or another, the social sciences will, eventually, be Darwinized.

Darwinian Psychology: Where the Present Meets the Past
By Debra Lieberman and Martie Haselton

Debra Lieberman is Assistant Professor in the Department of Psychology at the University of Miami.

Martie Haselton is Associate Professor in the Departments of Communication Studies and Psychology at the University of California, Los Angeles.


200 years after Charles Darwin’s birth and 150 years after the publication of “On the Origin of Species”, the field of psychology is traveling back to its roots as a life science, integrating the same principles biologists use to understand non-human life forms to understand human behavior and cognition. Darwin’s theories of natural and sexual selection identified the primary forces that shape both physiological structures and psychological mechanisms alike. Combined with the recent theoretical advances offered by genic selection and inclusive fitness theory, Darwin’s principles have proved to be invaluable tools for mapping the structure of the modern human mind and linking it with our long evolutionary history. For instance, we now know that the threats our ancestors faced left their legacy in the particular fears and phobias humans are most likely to acquire – fears of fanged creatures like spiders and snakes, but not of modern-day threats like the guns and fast moving cars that are far more likely to kill us today. Research applying Darwinian principles has also shown that kinship is a privileged social relationship, governed by specialized psychological mechanisms that infer relatedness based on ancestrally available cues that reliably distinguished kin from non-kin and between different types of kin. We have also discovered that human females, like our mammalian cousins, have an estrus phase of the cycle in which their sexual preferences and behaviors shift in reproductively sensible ways. These, and the many other discoveries enabled by the application of evolutionary tools, would not have been made without Darwin’s grand theory.

Looking forward, the application of evolutionary principles continues to permeate different subdisciplines within psychology including clinical science, cognitive psychology and neuroscience. More and more, Darwin’s influence can be seen in research programs investigating, for instance, whether particular clinical “disorders” are in fact psychological adaptations, the domain specificity of memory and attentional processes, and the specialized circuits involved in processing particular emotions. Despite widespread application, obstacles remain. Darwin’s theory is beautiful yet deceptively simple. It is often misapplied – for example, by assuming that adaptations work for the benefit of the group or species or by side-stepping rigorous consideration of the historical selective pressures leading to the evolution of a particular capacity. This will only continue if psychologists do not receive serious training in evolutionary biology. The study of the human mind must be grounded in biology, the study of life. Of course, there are those who oppose the full integration of biological theorizing into psychology, but this is based on concerns that, at least to us, are largely outdated. It is our hope that new generations of psychologists and social scientists will be fluent in Darwinian principles and modern evolutionary biology and that just as Darwin predicted, “psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Much light will be thrown on the origin of man and his history” (Darwin, 1859, pp 428).

Darwin, C. (1859). On the Origin of Species by Means of Natural Selection. London: John Murray.

Psychology's Best Discovery Heuristic
By Edouard Machery

Edouard Machery is Associate Professor in the Department of History and Philosophy of Science at the University of Pittsburgh.


Psychologists have often relied on unreliable technological metaphors to develop hypotheses about the nature of the human mind. Freud’s psychoanalytic hypotheses were inspired by the then prevalent hydraulic metaphor, which compared desires, emotions, and urges to fluids, while cognitive scientists have more recently been looking for psychological counterparts of the processes and systems making up digital computers (think of, e.g., working memory as the counterpart of a computer’s CPU and of attention as the counterpart of the allocation of computing power to different softwares). As Gigerenzer (1991) has shown, statistical tools such as, e.g., linear regression or bayesianism, have also often been turned into hypotheses about the nature of human psychological processes.

In contrast to these unreliable and often unprincipled discovery heuristics, evolutionary theory provides psychology with a well-motivated and powerful method for discovering human psychological traits. Nobody seriously denies that the mind is made of evolved traits, and, in combination with discoveries about animal behavior and psychology, archaeological findings, and anthropological data from hunter-gatherer studies, evolutionary theories can lead psychologists to develop plausible hypotheses about the nature of these evolved traits. In fact, because these are likely to be our best discovery heuristics, evolutionary theories should guide psychologists’ efforts to understand mind and behavior.

But there’s a catch: Taking evolutionary theory seriously has costs. Although psychologists rarely have the time and competence to engage with the burning controversies within evolutionary biology, they should keep up with the developments of evolutionary thinking instead of relying on somewhat outdated theories. Furthermore, showing that some psychological trait evolved and, a fortiori, that it is an adaptation is more difficult than is typically acknowledged by evolutionary-minded psychologists. These should be willing to broaden the toolbox they currently use, and to make place for the sources of evidence biologists view favorably.

Gigerenzer, G. (1991). From tools to theories: A heuristic of discovery in cognitive psychology. Psychological Review, 98, 254-267

Survival of the Fittest?
Just what does Darwin tell us about the human mind?

By Gary Marcus

Gary Marcus is Professor of Psychology at New York University.


Few phrases in science are as powerful – or as widely misunderstood – as the words “survival of the fittest.”

The problem with the phrase (actually coined by Darwin’s contemporary Herbert Spencer) is that it is perfectly ambiguous. On the one hand, “survival of the fittest” could mean “of all the possible creatures that one might imagine, only the fittest possible creatures survive” on the other, it could mean something considerably less lavish: not that the fittest possible creatures survive, but only that creatures that survive tend to be the fittest that happen to be around at any given moment.

This seemingly subtle difference – between “fittest among the choices that happen to be laying around” – and “fittest imaginable” – makes all the difference in the world. “Better than one’s neighbor” is a far cry from “best possible.”

Discussions of evolutionary psychology sometimes seem to be premised on the first. Human beings do such and such because such and such was the optimal (“fittest”) thing for our stone-age ancestors to do. Men like women with smooth skin because (prior to the advent of plastic surgery), smooth skin was a reliable predictor of fertility, so it was in the interest of our ancestors’ “selfish genes” to create brains with a preference for smooth skin.

While talk of function certainly has its place, examples like the injury-prone human spinal column (an unwise modification of the more sensible horizontal spine of our four-legged ancestors) suggest that the usual considerations of optimal function should be supplemented with consideration of what one might call evolutionary inertia. Just as objects in motion tend to stay in motion (Newton’s second law), evolution tends to modify what is already in place, rather than starting from scratch.

Consider human memory, which is far less reliable than computer memory. Whereas it takes the average human child weeks or even months or years to memorize something as simple as a multiplication table, any modern computer can memorize any table in an instant – and will never forget it. Why can’t we do the same?

Whereas computers organize everything they store according to physical (or logical) locations, with each bit stored in a specific place according to some sort of master map, we have no idea where anything in our brains is stored. We retrieve information not by knowing where it is, but by using cues or clues that hint at what we are looking for.

In the best case, this process works well: the particular memory we need just “pops” into our minds, automatically and effortlessly. The catch however is that our memories can easily get confused, especially when a given set of cues points to more than one memory. What we are able to remember at any given moment also depends heavily on the accidents of which bits of mental flotsam and jetsam happen to be mentally active at that instant. Our mood, our environment, even our posture can all influence our delicate memories.

Our memories may work in this fashion not because that is the optimal solution, but simply because, at the time of human evolution, cue-dependent memory was a firmly entrenched off-the-shelf part: cue-driven memory and all its idiosyncrasies has been found in just about every creature ever studied, from worms to flies, from spiders to rats, from monkeys to humans.

The structure of human memory might thus exist as it does not because it is the ideal solution (fittest possible) but simply because it was the fittest solution that was readily available (Marcus, 2008).

Marcus, G. (2008). Kluge: The haphazard evolution of the human mind. Boston, MA: Houghton-Mifflin.

An Open Letter to Comparative Psychologists
By Daniel J. Povinelli, Derek C. Penn, and Keith J. Holyoak

Daniel Povinelli is James S. McDonnell Centennial Fellow and Professor of Biology at the University of Louisiana.

Derek Penn is Affiliate Scientist at the University of Louisiana.

Keith Holyoak is Distinguished Professor of Psychology at the University of California, Los Angeles.


Darwin believed that earthworms have a sense of consciousness and that plants can hear bassoons. He claimed that “higher” animals have an incipient capacity for empathy, logic, language, magnanimity, an appreciation of beauty and a nascent belief in God. And he believed that dogs have a “sense of humor as distinct from mere play” and “possess something very like a conscience.” (Darwin, 1871).

Darwin’s anthropomorphic view of animals was as unfounded and unnecessary as his theory of pangenesis: Nothing about Darwin’s theory of evolution requires—or even suggests—that there be a seamless psychological continuity among living species. And yet, over the last quarter century, many comparative psychologists have stubbornly championed Darwin’s quaint idea that there are no “fundamental differences” between the mental capacities of humans and animals and have made anthropomorphic claims about nonhuman cognition as unsubstantiated as Darwin’s.

Even those comparative researchers who acknowledge that there might be something qualitatively different about the human mind have largely attributed the discontinuity to particular domain-specific faculties—such as language or social-communicative intelligence—and have denied that there might be a more profound, domain-general discontinuity between human and nonhuman minds.

The evidence clearly suggests otherwise: Only humans make fire, fashion wheels, draw maps, diagnose each other’s illnesses, risk their lives for ideals, punish strangers for breaking the rules, explain the world in terms of unseen causes, plan for hypothetical scenarios, take others’ welfare into account and teach each other how to do all the above. The evolution of all these uniquely human abilities begs for explanation.

It is possible that each of our uniquely human kinds of cognition results from a separate, domain-specific innovation. And it is possible that they all somehow arise from language. But it seems much more likely to us that some central cognitive capability co-evolved with and continues to subserve all our uniquely human abilities. According to our hypothesis (Penn, Holyoak, and Povinelli, 2008), this central cognitive capability was the ability to reason about higher-order relations and the core innovation that gave rise to the human mind was our brain’s ability to approximate the relational capabilities of a physical symbol system.

We are not sure that our hypothesis is correct but we are sure of this: It is time for comparative psychologists to move beyond a faith-based belief in the “mental continuity” between all species and to invest as much effort in identifying the differences between human and nonhuman minds as they have invested in identifying the similarities. Only then will comparative psychology be able to take its rightful place at the roundtable of cognitive science.

Darwin, C. (1871). The descent of man, and selection in relation to sex. London, John Murray.

Penn, D. C., Holyoak, K. J., & Povinelli, D. J. (2008). Darwin's mistake: Explaining the discontinuity between human and nonhuman minds. Behavioral and Brain Sciences, 31(2): 109-178.

Evolution of Human Sex Differences
By Wendy Wood and Alice H. Eagly

Wendy Wood is Professor of Psychology and Neuroscience and Professor of Marketing at Duke University.

Alice Eagly is Professor of Psychology at Northwestern University.


Charles Darwin, while offering a brilliant analysis of species development and change, struggled to understand human distinctions of race, class, and gender. In Darwin’s analysis, these distinctions arose from sexual selection processes. For example, he explained the presumably superior beauty of the aristocracy as due to upper class men successfully competing for and choosing the most attractive women from all social classes. Like Darwin, contemporary evolutionary psychologists explain men’s universally greater size and strength along with their tendencies toward psychological aggressiveness and competitiveness as due to sexual selection mechanisms of male competition and female choice.

Modern evolutionary thinking has progressed beyond such a simple analysis, in part because evidence from comparative studies of primates questions whether human sex differences originated in sexual selection. The human male-female size difference is low in magnitude compared with other primate species, and species with low dimorphism have a large variety of behavioral patterns and social structures (Plavcan & van Schaik, 1997). In addition, both female and male size are products of multiple selection pressures. Such findings call for more complex evolutionary accounts of humans’ physical and psychological sex differences.

Our evolutionary analysis of sex differences takes into account humans’ considerable behavioral flexibility in response to local circumstances. This characteristic feature of humans reflects their evolution in diverse environments with changeable conditions that impinged in differing ways on survival and reproductive outcomes (Wood & Eagly, 2002, in press). For example, in the late Pleistocene era, climate appears to have been highly variable. Also, humans and their ancestors engaged in extensive niche construction, meaning that their activities altered the environments in which they lived. Accommodating to such changes required behavioral flexibility, enabled by an evolved capacity for innovating and sharing information through social learning, yielding a cumulation of culture. Humans’ flexibility is evident in their various novel solutions to the problems of reproduction and survival, including tolerance for a wide range of foods, ecologies, and living arrangements.

Given these selection pressures on human ancestors, sex differences in behavior arise flexibly from a biosocial interaction in which sociocultural and ecological forces interact with humans’ biology as defined by female and male physical attributes and reproductive activities (Wood & Eagly, 2002). Specifically, women bear and nurse children, and men possess greater size, speed, and upper-body strength. Given these attributes, a division of labor arises such that certain activities are more efficiently accomplished in certain societies by one sex than the other. For example, women are limited in their ability to perform certain tasks incompatible with childcare (e.g., requiring speed, uninterrupted activity). Therefore, women in foraging, horticultural, and agricultural societies generally eschew tasks such as hunting large animals, plowing, and conducting warfare. Nonetheless, under certain social conditions that lessen these constraints, women have taken on roles of warriors and hunters. Recently, the division of labor and gender hierarchy have become less pronounced, reflecting the declining importance of physical sex differences due to lowered birthrates and decreased importance of size and strength for high status roles. The resulting political and social changes give women access to a greater range of social roles and have altered female psychology.

Plavcan, J. M., & van Schaik, C. P. (1997). Interpreting hominid behavior on the basis of sexual dimorphism. Journal of Human Evolution, 32, 345–374.

Wood, W., & Eagly, A. H. (2002). A cross-cultural analysis of the behavior of women and men: Implications for the origin of sex differences. Psychological Bulletin, 128, 699-727.

Wood, W., & Eagly, A. H. (in press). Gender. In S. T. Fiske, D. T. Gilbert, & G. Lindzey (Eds.), Handbook of social psychology (5th ed.). New York: McGraw Hill.


Biology_Unit 11_Quiz 1: Animal Behaviors. NOTES.

1.What mechanisms are causing the behavior?
2.How does the behavior develop?
3. What is its survival value?
4.How did it evolve?

Keep in mind that this doesn't mean that because a child's parents are shy, there is a shy gene passed down to make the child shy as well. The child could learn the shy behavior by simply observing and emulating this behavior. There always seems to be a combination of both nature and nurture in influencing behavior.

Evolution. Evolution is based on genetic inheritance. A change in the genotype of an organism is passed down from parent to offspring again and again. Over time, the genes in a population change and the phenotype of an organism is altered. Animals seem to evolve in a way that best helps them to survive or adapt to their environment. Imagine a population of jaguars. Some are fast runners, which allows them to easily catch prey. The rest of the jaguars are slow runners, which makes it more difficult to catch prey. Since they do not catch prey as easily, the slow jaguars die more often than the fast jaguars because they cannot eat. The slow jaguars also reproduce less often than the fast jaguars. Since more fast jaguars reproduce than slow jaguars, most offspring inherit the gene for fast running. This favorable gene is continually passed down from parent to offspring.
This example is similar to the passing on of behaviors, and how behaviors evolve due to the greatest fitness for the species. This is called the optimality theory. If a behavior benefits a species more than it costs the species, it will be repeated and passed on for generations. Thus, each species has its own unique evolutionary history in behavior as well as in its evolutionary history of anatomy and physiology.
Physiology. What are our physiological needs? In order to function properly, we need to eat, sleep, drink, breathe, etc. How does your behavior change if you don't meet a physiological need? If you don't eat, you might become grumpy. Some people may even steal in order to feed themselves. Animals are similar. Their basic needs must be met as well, and their behavior coincides with getting these needs met. Although all organ systems are involved in producing a behavior, the nervous and endocrine systems have the most influence. The nervous system is the communicator of the body. It receives a stimulus and directs a response. The endocrine system produces hormones that also communicate with different parts of the body. The relationship of the endocrine system is commonly seen when it's time for animals to mate or breed. For example, male sheep get along well with other males until mating season. At this time, their reproductive organs drop, sperm are produced, and male hormones are activated. This, in turn, affects the animal's physiology and behavior. The male sheep are now territorial and fight other males to attract females.

Habituation. Tube worms instinctively cringe into their tube when a shadow passes over them. This is because the shadow often belongs to a predator. However, place this worm in a controlled environment where a shadow is cast over it without any consequence, and the worm will learn that there is no threat and stop hiding. Habituation is learning not to continue a behavior due to a lack of reinforcement for that behavior.

Classical conditioning. Pavlov's experiment is a typical case of classical conditioning in which an instinctive response or behavior to a stimulus is learned for a different stimulus. The dog's instinctive behavior is to salivate to food. The dog was conditioned to associate a bell with food because every time a bell rang, food was presented. So the dog began to salivate not just to food, but to a different stimulus—a bell.

Operant conditioning. If you give a dog a treat every time you tell it to sit, it will continue to sit when asked. This is the basis of operant conditioning in which a learned behavior becomes more frequent or infrequent due to rewards or consequences. An experiment was conducted in which a hungry rat was placed in a box. The rat crawled and sniffed all over the box, exploring it. During this exploration, it discovered a button in the box that distributed food if it was pressed. The rat began to push the button more frequently and then more exclusively anytime it wanted a piece of food. It was conditioned to learn that if it pushed the button, it would receive a reward—food.

Latent learning. Animals can learn without reward or reinforcement. Latent learning is when an animal learns a new behavior without receiving an immediate reward. In fact, the discovery or information learned may not be expressed until a situation calls for it. It's like watching your dad tighten a screw. Later in life, you may find a loose screw, grab a screwdriver and tighten it, just like your dad did, without any additional instruction needed. Simple exploration by the animal is often the example used with latent learning. For example, a hollow piece of wood was placed in a chipmunk's habitat. The chipmunk sniffed and explored the wood and then went on its way. A cat was then placed in the chipmunk's area. The chipmunk ran directly to the wood and hid beneath it.

Insightful learning. Insightful learning seems to be a more complex learning ability. It involves problem solving, insight, and planning. An experiment was done with monkeys. The monkeys were placed in a cage full of different toys like crates and sticks. Bananas were hung near the cage but out of the monkeys' reach. After many attempts to reach the bananas, the monkeys became frustrated and finally gave up. Then the monkeys noticed the toys available to them. They explored the different toys, and some attempted to stack the crates to reach the bananas others tried to reach the bananas with a stick. One found a way to attach two sticks together so it was long enough to reach the bananas. Insightful learning is a sudden appearance of different behaviors that solve a once unsolvable problem.

Social learning. We have all picked up habits or learned a behavior by watching and doing as others do. That is the basis of social learning. Social learning occurs automatically with many offspring. Newborn animals spend a lot of time with their parents, following them around and watching how to hunt and where to find food and water, etc. If you set a bird feeder out in your backyard, birds won't come and start feeding right away. But once one or two discover the bird feeder and start to feed, more birds then come. This is because other birds are watching and learning from the others.

Behavior in movement. A major difference between plants and animals is that animals move from place to place. They move to satisfy physiological needs. Roly-poly bugs, for instance, thrive in moist conditions. They'll move around in no particular direction till they find a wet spot and then stay there. This simple movement is called kineses and is mainly due to environmental conditions. Some animals, like moths or earthworms, move toward or away from light sources. Movement based on a stimulus is called taxis. It is similar to tropisms in plants. Like phototropism, phototaxis is when an animal's movement is toward or away from a light source. A type of movement by animals you may be more familiar with is migration. Periodically, animals will move or migrate to a different area to seek food, mates, or shelter. Birds flying south for the winter is an example of a migration. Salmon migrate upstream during a certain season to mate. Many animals migrate for various reasons.

Food search. Animals behave in a certain way to find food. Some are very particular with what they eat others are not. Each has its own way to get food. Filter feeding is done by most aquatic invertebrates, like sponges, and some vertebrates, like the Baleen whale, which swallows huge amounts of water to be filtered for food and nutrients like plankton. Some animals, like herbivores, take advantage of their immobile and plentiful food source—plants. Herbivores can save the energy to hunt or chase after their food source. Carnivores are those animals that eat other animals. Thus, these animals must find and capture prey and avoid being captured themselves unless they're on top of the food chain. The optimality theory of animal behavior suggests that the behaviors which evolve are those that benefit the animal the most. Many predators have the ability to strategize. They need this ability to obtain food. And most predators can assess the environment, choose a prey that is abundant and easy to obtain, and cooperate with others in a capture.

Avoiding capture. Unless an animal is at the top of the food chain, it's at risk for becoming lunch! Thus, most animals must always be on the defense. One way to do this is to avoid being detected. Many animals will freeze up if they hear an unfamiliar sound or feel or smell an approaching predator. Some animals can blend into their settings by the color of their fur or skin, which may change with the seasons. They can resemble other objects, like leaves or twigs of a tree, as well. Animals may have chemical or physical defenses, like the spray from a skunk or the stinger of a wasp.

Some animals employ the use of mimicry to escape predation. In biology, mimicry is the imitating of an organism (the mimic) from another organism (the model). The mimicry of a trait or traits helps the mimic to survive. There are two major types of mimicry, Batesian and Müllerian. In both types of mimicry, one species copies another to escape predation. A harmless moth that resembles a wasp would be an example of Batesian mimicry. The moth is the mimic and the wasp is the model. The nontoxic moth is unable to sting another animal, but mimics the yellow jacket wasp that is able to sting another animal. Müllerian mimicry is one in which both the mimic and the model are both dangerous to the potential predator and there is no distinction between the mimic and the model. An example of this would be the yellow jacket wasp and the bumblebee. Both of the species possess bright yellow and black colors and are able to use their sting as a defense method.

Like the optimality theory suggests, the benefits outweigh the costs, so many animals tend to cooperate with one another to reach the common goal of survival. Cooperation can be within the same species or between organisms of different species. A pack of hyenas, for example, can attack and kill larger prey if they work together than if they try to hunt individually. Similarly, a flock of geese can save energy during migration by flying together. Have you ever run behind someone on a windy day? The person in front of you creates a shield that protects you from the wind, making your run easier. The lead goose in the classic V formation does the same thing. He shields the other geese from the wind, making their flight easier. When the lead goose gets tired, he moves to the back of the formation and another goose takes his place.

Communication. Like in any family, organization, or group, communication is key. Animals communicate in many different ways, with similarities to how humans communicate. While we speak in different human languages, animals have their own language in the noises they may make, like barking, whistling, chirping, or croaking. Noises can attract mates or send out distress or alarm signals to others in the group. While we can communicate nonverbally in our facial expressions, tone, or gestures, animals also make nonverbal physical gestures—for example, a cat warning a dog not to come near it by arching its back, hissing, and showing its teeth. A deer will raise its tail to warn others of a predator. As we can express affection or dislike by physical contact, some animals also communicate by touch, like the social grooming practices of monkeys. In sporting events, we compete against other teams to see who's dominant in the sport. Animals also establish dominance hierarchies by exhibiting physical strength against others. They have leaders, those second in line, those third in line, etc. Some animals use scent or odor to communicate—like a dog marking its territory. Group identity is also exhibited by scent. For instance, an ant that smells different from the other members of a group will be attacked.

Mutualism. In mutualism, both species benefit. The benefits can occur with a resource traded for another resource, like in the example of fungi and orchids. The fungi feed on the roots of the plants, pulling out carbohydrates, while at the same time making nitrogen and phosphates for the plant to use. There is also a resource traded for a service relationship in mutualism. For example, insects and birds receive nectar from flowers, and, as a result, they help conduct pollination for the flower. In some cases, a service-for-service relationship can be seen—like with ants that nest in acacia trees. These ants help protect the tree by attacking herbivores while the nesting grounds in the tree's thorns protect the ants from predators.

Mutualism has significantly contributed to the biodiversity of organisms you see today. Many organisms depend on mutualistic relationships to continue their species.

Commensalism. In commensalism, only one organism benefits, but the other is not harmed. There are many ways in which organisms benefit from commensalism. Some organisms have a special type of commensalism called phoresy. In phoresy, one organism attaches itself to another organism for the purpose of transportation. Barnacles, for example, are marine organisms that cannot move on their own. Instead of remaining in one place, barnacles attach themselves to the shells and skin of other animals. The barnacles gain a mode of transportation, but the other organism gains nothing. Another example of phoresy is the remora fish that attaches itself to sharks. The remora gains transportation and protection from the shark. The shark is not harmed by the relationship, but it is not helped either.

Other organisms benefit from commensalism by gaining access to food. Cattle Egrets are a bird species that live among livestock, such as cattle and horses. The birds feed on insects stirred up by the movement of the grazing animals. The egrets benefit from the relationship, but the livestock do not. Commensalism also helps some plant species spread their seeds. Burdocks are common weeds found in fields and along roadsides. The seed heads of burdocks have long, curved spines, like a fishhook. The hooks catch onto the fur of passing animals and are carried away from the parent plant. When the seed heads fall off, they are able to grow in a new environment.

Do you know anyone who has a hermit crab? Hermit crabs have soft bodies, but they cannot grow their own shells. Instead, they use the shells of dead organisms, such as snails, for protection. Anemonefish, commonly called clownfish, also benefit from the protection of another organism. Clownfish live inside sea anemones. The long, poisonous tentacles of the sea anemone protect the fish from predators. In both situations, one organism benefits, but the other does not.

Biologists argue that true commensalism is rare, if not nonexistent. Most commensal relationships have at least a small effect on the second organism. The organism may appear to be unaffected, but it may be helped or harmed in a subtle way. For example, when barnacles attach to another organism, they add weight. It is not yet known if the extra weight harms the second organism. On the other hand, an organism with barnacles attached to it may be less of a target for a predator. It may actually benefit the organism to have barnacles.

Parasitism. Parasitism is a relationship between two organisms which hurts one and helps the other. The organism that is helped is called the parasite. The organism that is harmed is called the host. In many cases of parasitism, the host is not only hurt, it is killed. A common example of a parasitic relationship is athlete's foot. The athlete's foot fungus grows on a person's skin and may cause serious infection if not treated properly. Other parasitic relationships include lice, ticks, and fleas.

Parasites can live on or in the body of a host. Those that live on the outer body of a host are called ectoparasites and those living inside a host are called endoparasites. A tapeworm is an example of an endoparasite that lives in the intestines of a larger animal. A tick is an example of an ecotoparasite which attaches to the skin of an animal and feeds off the animal's blood.

Most parasites harm their hosts by eating tissue or releasing poisonous chemicals. Have you ever accidentally cut your skin with rusty metal? If so, you probably went to the doctor for a tetanus shot. Bacteria that often live on old metal items secrete chemicals that interfere with nerve impulses in the body.

There are two main types of parasitic relationships. The first is like a hit and run. The parasite lives on the host for a short period of time and then moves on to another organism without killing the first. Ticks are an example of short-term parasitism. The second type of relationship is long-term. The parasite stays with the host until it dies, or until both organisms die. Blood flukes are a type of flatworm that live in the veins of their hosts. The flukes remain with the host until the host dies.

Many biologists believe that parasitism is one of the most powerful forces of evolution. In a parasitic relationship, it is beneficial for both the parasite and the host to evolve and adapt. As adaptations give the host greater protection against the parasite, the parasite also adapts by attacking in new or stronger ways. Have you heard of "super germs"? The term refers to a new strain of antibacterial-resistant bacteria. As humans developed new ways to kill bacteria, the bacteria evolved and are now able to withstand most medications.


Demography and Cultural Evolution

The growth and age structure of human populations are both affected by norms and beliefs of their members. A predominantly agricultural lifestyle produced higher population growth than the hunting-gathering lifestyle it replaced (148, 149). This increased growth was most likely due to the spread of a complex of cultural traits (150) whose adoption may have created conditions that favored the accumulation of subsequent culturally transmitted behaviors (151, 152). Beginning in the late 19th century, parts of Europe, Asia, the United States, Australia, and New Zealand began to undergo a second demographic transition, which involved a change from a high birth rate, high mortality regime to a lower birth rate, low mortality regime. These changes were due to the spread of fertility-reducing and survival-increasing behaviors that became part of the developed countries’ cultures.

Standard quantitative models of demographic change do not include within-population variation in behaviors that affect fecundity or mortality. Projections usually use fixed values for birth and death rates however, religious preferences, marriage customs, dietary choices, population subdivision, and mortality profiles may affect fecundity but are usually not part of demographic models. Further, aspects of cultural transmission, such as prestige bias and the choice of nonparental cultural role models, can facilitate the spread of fertility-reducing behaviors (12, 153). Thus, cultural evolutionary approaches should be integrated into demography, especially the processes that have led to fertility decline (154).

Many models for life history analysis of humans divide the lifespan into an ordered series of age classes. These models first define the fertility rates of each age class and the survival rates from one age class to the next. Then, they iterate the number in each age class produced by these parameters to determine the dynamics of the population, including whether the number in each age class approaches a stable equilibrium, termed the stationary age distribution, or whether the population will grow or go extinct and at what rate (155).

Carotenuto et al. proposed a demo-cultural framework for such an age-structured population, in which each individual carried one variant of a dichotomous trait, say H or h, where H represents the presence of a socially learned behavior (for example, fertility control) and h is its absence (156). An individual of type H might also be more likely to survive into the next age class. This integration of demography and culture yields complex dynamics for example, the trait H can persist in the populations even if it lowers fertility, as long as the cultural transmission of H is reliable enough, or if H also sufficiently increases the chance of survival. Additional learning steps can also be added to age-structured models, such that vertical and horizontal transmission can occur at different rates for different age classes (101). In this case, horizontal learning accelerated the trait’s spread and led to faster population growth than vertical transmission alone.

An important outgrowth of demo-cultural modeling has been its application to the sex-ratio problem. In many places, the sex ratio at birth is strongly biased in favor of males and, in China and parts of India, has resulted in up to 120 male births for every 100 female births (157). This cultural preference for sons can be manifested in sex-selective abortion or withholding of resources from daughters. This bias has both economic and socio-cultural antecedent, as well as important ethical and demographic consequences (158).

Data on cultural transmission of son preference can be incorporated into formal demographic analysis (159), linking these data to real-world policy applications (160). Theoretical models can also aid in predicting the effects of policies: For example, one such model tracked the cultural transmission of the perceived present value of a son relative to a daughter, the sex ratio at birth, and their effects on demographic change (161). The results of this model suggest that interventions focused on peer-to-peer cultural transmission of a perceived higher value of daughters might complement existing economic incentives to support and educate daughters, with the goal of mitigating the effects of son preference. The literature on the interaction between cultural transmission and formal demography is quite sparse. Given the large variety of customs that relate to birth and death rates in different human societies, population projections for the future needs of diverse populations should incorporate more cultural dynamics than is currently standard practice.


6. Conclusion

The social reality of modern human culture is the single characteristic that marks our species off from all others. It is rooted within the capacity of individuals to learn, specifically within the ability to learn from other members of our species. Its uniqueness must lie within the combination of human cognitive and social mechanisms that give rise to social reality. Whether it be judged as a specific type of adaptation is questionable what is not is that it lies within a continuum of selection processes that extends from evolution itself, through individual development and individual learning, and on to cultural change. What also cannot be doubted is its capacity to add hugely to human diversity in the form of cultural differences.

One of the unfortunate features of nineteenth century biology that extended into that of the twentieth century was a tendency to ascribe absolute causal difference to biological and social𠄼ultural force. That was scientific nonsense that gave rise to some damaging, at times, deadly ideologies. We should never allow science to be distorted and to serve destructive forms of social reality. That is what is so puzzling about human culture. It is a part of human nature, and yet can give rise to calamitous beliefs and events for our own species.


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