In the Light of Evolution: Two Centuries of Darwin. National Academies Press US ; Charles Darwin laid the foundation for all modern work on sexual selection in his seminal book The Descent of Man, and Selection in Relation
Sexual selection modern humans Sex.
In this work, Darwin fleshed out the mechanism of sexual selection, a hypothesis that he had proposed in The Origin of Species. He went well beyond a simple description of the phenomenon by providing extensive evidence and considering the far-reaching implications of the idea. Here we consider the contributions of Darwin to sexual selection with a particular eye on how far we have progressed in the last years.
We focus on 2 key questions in sexual selection. First, why does mate choice evolve at all?
And second, what factors determine the strength of mate choice or intensity of sexual selection in each sex? Darwin provided partial answers to these questions, and the progress that has been made on both of these topics since his time should be seen as one of the great triumphs of modern evolutionary biology.
However, a review of the literature shows that key aspects of sexual selection are still plagued by confusion and disagreement.
Although we have made significant progress in some areas of sexual selection research, we still have much to accomplish.
C harles Darwin proposed the concept of sexual selection years ago in On the Origin of Species by Means of Natural Selection Darwin,but his definitive work
Sexual selection modern humans sexual selection was undoubtedly The Descent of Man, and Selection in Relation to Sex Sexual selection modern humans was published in In typical Darwinian fashion, The Descent of Man, and Selection in Relation to Sex is a colossal tome with a tongue-tripping title that we will henceforth abbreviate as The Descent of Man that strolls through myriad topics relevant to evolutionary biology and ecology.
Consequently, it is futile to attempt to characterize the full spectrum of topics addressed in this book, which touched upon such sundry issues as species concepts, taxonomy, correlated evolution, sex-limited inheritance, and group selection, to name a few.
Rather, we focus on the contributions of Darwin in light of modern research in sexual selection, and in so doing we identify a few important topics for which a thread of reasoning can be traced from Darwin to the present.
One of the great strengths of Darwin was that he often constructed his literary works with a clear argument in mind and marshaled vast amounts of
Sexual selection modern humans to support his case.
Darwin believed that sexual selection played a major role in the evolution of humans and the divergence among distinct human populations, so he felt a lengthy description of sexual selection was necessary.
It is difficult to find a quote from Darwin that captures the full essence of his concept of sexual selection, but he provides the following definition:. We
Sexual selection modern humans, however, here concerned only with that kind of selection, which I have called sexual selection. This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.
However, Darwin makes it clear that not all selection related to reproduction constitutes sexual selection, as primary sexual traits—like ovaries and testes—can evolve as a consequence of natural selection. Aside from the definition of sexual selection, what did Darwin accomplish in The Descent of Man? Here we try to focus on those parts of the book that are still relevant to modern research, and from our perspective Darwin identified 2 major themes that set the stage for work on sexual selection.
The first theme concerned the question of why sexual selection occurs in the first place. The second theme is related to the question of why sexual selection is strong in some lineages but not others. This question continues to be a major theme of modern research, but Darwin expressed
Sexual selection modern humans amazingly modern, intuitive understanding of some of the explanations for the patterns of sexual selection among diverse evolutionary lineages Darwin, Rather than review all of the relevant literature, which for many of these topics has been done recently, we try to paint the current state of sexual selection with broad strokes.
Like Darwinwe focus on precopulatory sexual selection, leaving the treatment of postcopulatory processes for a different chapter in this volume Eberhard, Chapter Our sojourn through sexual selection literature leads to the identification of at least 2 major triumphs of precopulatory sexual selection research since Darwin. It also identifies numerous areas ripe for additional work. His original definition of sexual selection, which appeared in The Origin of Speciesappears to emphasize male-male combat [i.
Thus, Darwin identified the 2 main categories of sexual selection that persist to this day. Sexual selection would be relatively simple if there were nothing but what we call intrasexual selection.
In some species, males engage in fierce struggles among one another, and the victors in these contests tend to mate with the receptive females. Darwin provided numerous examples of species in which intrasexual combat for access to mates prevailed, some of the more interesting of which
Sexual selection modern humans male narwhals fencing with their tusks [which remains to be studied, but see Gerson and Hickie ], male scarab beetles family Scarabaeidae battling with their elaborate horns Emlen et al.
However, intrasexual selection is not a sufficient mechanism by which to explain all of the diversity wrought by sexual selection.
Modern work shows that intersexual selection is a major aspect of sexual selection, a point that was deeply appreciated by Darwin. The female could in most cases escape, if wooed by a male that did not please or excite her; and when pursued, as so incessantly occurs, by several males, she would often have the opportunity, whilst they were
Sexual selection modern humans together, of escaping with, or at least
Sexual selection modern humans pairing with, some one male.
If the number of words devoted to each topic can serve as a guide, then Darwin felt that the
Sexual selection modern humans of female choice required much more explanation than did male-male combat.
Here we will treat female choice, while keeping in mind that Darwin "Sexual selection modern humans" that in some systems mirror-image processes could occur through male choice. Sexual selection as a consequence of female choice is easy to understand, provided we are willing to accept that female preferences exist. If females show a preference, then males with the preferred trait will leave greater numbers of offspring, and their trait values will tend to increase in frequency in the population.
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But why would
Sexual selection modern humans preferences exist in the first place? The answer to this question is not entirely obvious. Numerous passages in The Descent of Man address this issue, the following quote among them:. Nevertheless, when we see many males pursuing the same female, we can hardly believe that the pairing is left to blind chance—that the female exerts no choice, and is not influenced by the gorgeous colours or other ornaments with which the male alone is decorated.
Given the variation among males with respect to their beautiful ornaments, it is difficult to believe that females have no preference whatsoever, and even a weak preference would be sufficient for sexual selection to operate. Hence, Darwin clearly understood that female preferences existed, but he never compellingly explained why such preferences would
Sexual selection modern humans. Indeed, Darwin himself seemed to subscribe to this point of view, as he went to great lengths to argue that arthropod, insect, and vertebrate females possess sufficient intelligence to appreciate beauty.
However, Darwin also clearly appreciated that different spe cies could possess different standards of beauty, explaining why not all sexually selected traits appear attractive to us. It can be argued that it took almost years for the study of sexual selection to overcome this erroneous view of mating preferences.
The study of sexual selection entered its modern era during the latter half of the 20th century when scientists identified the evolution of female choice as a legitimate topic in its own right by expanding the ideas laid out much earlier by Fisher In other words, it was no longer sufficient to assume that females had preferences or even to provide empirical evidence of such preferences. Once the evolution of preferences could be explained, our understanding of selection of the preferred trait became entirely straightforward, and it remains today essentially as Darwin described it.
Thus, the difficulty, which partly remains unsolved, is to understand the evolution of female or male preferences. We will briefly review the modern models, but we start with the one explicit model proposed by Darwin. Although his model is missing some elements and comes up short
Sexual selection modern humans a complete explanation for choice evolution, it does provide the core of a model with potential explanatory power.
Males also are variable in quality, and they arrive before females on the breeding grounds Fig. The higher-quality females are ready to breed
Sexual selection modern humans the lower-quality females, and they choose to pair with the higher-quality males Fig. However, theoretical models of sexual...
Thus, the model predicts assortative
Sexual selection modern humans by quality Fig. A First, males and females are variable with respect to phenotypic quality. B Males, which have the ornaments, move to the breeding area large circle before the females. C The highest-quality females more Such pairs would have an advantage in rearing offspring, more especially if the male had the power to defend the female during the pairing-season, as occurs with some of the higher animals, or aided in providing for the young.
Unfortunately, Darwin did not elaborate much on this line of reasoning, and he never provided a convincing explanation for the evolution of a preference for ornaments or other sexually selected characters not directly
Sexual selection modern humans in territory defense or parental care. However, surprisingly little research has been directed at this model, and so far it has been used exclusively as an explanation for sexual selection in males of monogamous taxa.
Additional theoretical and empirical work on this model is warranted, and attempts should be made to extend it to sexual selection on females and in nonmonogamous taxa.
Models for the evolution of mating preferences fall into 2 major categories: We provide a list of some of the most commonly invoked direct benefits in Table 9. The evolution of choice for direct benefits is conceptually simple, as the selective advantage to choosing is entirely obvious Andersson, However, the situation is slightly more complex when the female prefers an ornament in the male that somehow indicates that the male will provide better-than-average parental care, resources, defense, and so forth Table 9.
Under these circumstances, there must be a mechanism that produces a correlation between the secondary sexual trait and the direct benefit provided by the male to the female.
Our reading of
Sexual selection modern humans literature indicates that direct-benefits models enjoy excellent Sexual selection modern humans support and are mostly not controversial, so we will treat them no "Sexual selection modern humans" here.
In some species, the males appear to provide nothing to the females but sperm, yet they have elaborate ornaments for which females show preferences Taylor and Williams, ; "Sexual selection modern humans" and Gross, ; Kirkpatrick and Ryan, ; Kokko et al. These systems are especially perplexing from a sexual selection standpoint because the benefits of choice are not at all obvious. Consequently, a tremendous amount of effort has been devoted to creating explanatory models of female-choice evolution in such systems Lande, ; Kirkpatrick, ; Andersson, ; Mead and Arnold, Several excellent reviews have addressed the dizzying array of such models Kokko et al.
We would like to suggest that there are 3 main categories of indirect-benefits models. We have no doubt that such a categorization will be controversial.
Sexual selection modern humans, we are at odds with at least one other perspective that suggests that all indirect-benefits models should be lumped into a single category of Fisher-Zahavi models Eschel et al. We believe there is much heuristic value in "Sexual selection modern humans" them separate, so to stimulate discussion we propose the following 3 classes of models.
This model involves a single preference trait in females and a single ornament trait
Sexual selection modern humans males ignoring multivariate preferences and signals for the moment.
To understand this model, we must appreciate that females with a preference for a large ornament, for example, will have offspring with both the genes for the large ornament from the father and genes for the preference for large ornaments from the mother Fisher,; Lande, Consequently, mate choice results in a genetic correlation between the ornament and preference Lande, ; Mead and Arnold, The ornament evolves as a consequence of sexual selection imposed by female mate choice, and the preference is carried along as a consequence of a correlated response to selection Lande, Almost any outcome is possible in the Fisherian model, depending on the strength of the genetic correlation between the ornament and the preference Lande, ; Kirkpatrick, ; Mead and Arnold, However, under some circumstances, this model results in a self-reinforcing, open-ended process that produces never-ending trait elaboration.
Eventually, the process is opposed by natural selection when the ornament becomes so large as to be a major impediment to survival, a point that was actually well appreciated by Darwin It is also worth noting that some amount of a genetic correlation between ornament and preference will occur in any system in which mate choice operates, so a Fisherian process could act in concert with almost any other model of mate-choice evolution.
This model requires at least 3 traits i. In the condition-dependent indicator model, the ornament is a costly condition-dependent trait. Thus, males closer to the optimum with respect to the viability trait will be in better condition and will be able to maintain a more elaborate version of the ornament Zahavi, Female choice evolves because females choosing males with more elaborate ornaments produce offspring with higher viability or that will be in good condition as adults.
Of the indirect-benefits models, the condition-dependent indicator model works most easily from a theoretical standpoint and enjoys the most empirical support Andersson, Because the ornament is condition dependent, it is always a reliable indicator of genetic quality, and for female preferences to evolve or be maintained, the condition-dependent indicator model does not require any variation
Sexual selection modern humans the genes determining the ornament although the ornament may appear genetically variable due to genetic variation in condition. Search form
Of course, for the male trait to evolve it must be genetically variable. Charles Darwin laid the foundation for all modern work on sexual selection in his believed that sexual selection played a major role in the evolution of humans. UCLA psychiatrist Andrew Shaner is an expert on the modern extensions of Darwin's early insight relating sexual selection to human evolution. In terms of sexual selection, in humans as well as animals, there are two different the thin and tan "Sexual selection modern humans" women of the modern Western era.
Jordan Peterson: The successful male, sexual selection
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13. Sexual Selection
Can you me with this girl? UCLA psychiatrist Andrew Shaner is an expert on the modern extensions of Darwin's early insight relating sexual selection to human evolution. In terms of sexual selection, in humans as well as animals, there are two different the thin and tan ideal women of the modern Western era..
In the Light of Evolution: Two Centuries of Darwin. National Academies Press US ; Charles Darwin laid the foundation for all modern work on sexual selection in his seminal book The Descent of Man, and Selection in Relation to Sex. In this work, Darwin fleshed out the mechanism of sexual selection, a hypothesis that he had proposed in The Origin of Species. He went well beyond a simple description of the phenomenon by providing extensive evidence and considering the far-reaching implications of the idea.
Here we consider the contributions of Darwin to sexual selection with a particular eye on how far we have progressed in the last years. We focus on 2 key questions in sexual selection. First, why does mate choice evolve at all? And second, what factors determine the strength of mate choice or intensity of sexual selection in each sex?
Darwin provided partial answers to these questions, and the progress that has been made on both of these topics since his time should be seen as one of the great triumphs of modern evolutionary biology. However, a review of the literature shows that key aspects of sexual selection are still plagued by confusion and disagreement.
Many of these areas are complex and will require new theory and empirical data for complete resolution.
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This page was last edited on 9 November , at The Greatest Show on Earth: Humans do not typically mate like orangutans intermittent couplings between isolated individuals , gibbons isolated pairs , gorillas isolated one-male, multi-female units , or chimpanzees and bonobos promiscuous groups. Research seems to contradict Manning's explanation about skin color. Review of General Psychology. In the tropics, where abundant plant food enables women to provide much of the family's sustenance, polygyny is more common [ 83 ].
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MORE: Evolutionary advantage of sexual reproduction over asexual reproduction