In The Origin of Man and Sexual Selection, Darwin proposed the theory of sexual selection in addition to natural selection. For Darwin, the theory of sexual selection meant that animals also had strong emotions, keen intuition, and the ability to appreciate beauty. However, Wallace, the co-founder of the theory of chemistry, and his successors suppressed the theory for nearly a century.
Today, Richard Plum, a Yale ornithologist at Yale University, has used his more than 40 years of bird watching experience and 30 years of research on bird evolution to once again explain to the public this long-suppressed theory of evolution. He was desperate to reverse the fact that Darwin's theory of sexual choice had been marginalized...
"After carefully weighing various arguments against sexual choice theory, I still firmly believe in the truth of sexual choice theory." It was darwin's last expression of his belief in this evolutionary dynamic before his death.
More than a hundred years later, Yale ornithologist Richard Plum used his powerful articulation skills to once again illustrate this long-marginalized theory of evolution to the public. He followed Darwin entirely, advocating the stripping of sexual selection from the mainstream theory of natural selection and the establishment of a pure aesthetic theory that had nothing to do with natural selection.
The use of beauty as a key influence on evolution has plunged Prum into a huge whirlpool of controversy.
Is aesthetics unique to humans?
Birds are one of the most beautiful sounds in nature, but not all of them are made by the organs of speech. In 1985, Prum heard the sound of male plum-winged harriers in Ecuador for the first time, one moment "beep" and the other "hey hmm.". On closer inspection, it is a mechanical vocalization method that is emitted by flapping wings.
After more than 70 million years of evolution, the calls of traditional birds are perfect, so why do many independent species innovate a new way of sounding? What is even more puzzling is that in order to better use the wing feathers to make sounds, the male plum-winged petanel is forced to abandon the forelimb bones that existed long before the birds could fly, at the cost of reducing the male's flight ability, maneuverability and energy efficiency. And so on, this method of vocalization, which seemed completely unnecessary to Prum, even had the result of functional degradation. How can an obvious loss-making transaction be under the influence of natural selection? Natural selection always selects what is valid and useful.
The "wing-singing" behavior that Prum observed occurred in the courtship field of male plum-winged petites, a typical male ostentatious trait in order to gain the attention of the opposite sex.
If the subject of natural selection is a natural condition, then the male plum-winged petite is motivated by active courtship, and the outcome of the selection depends on the preference of the female.
Birds use their preferences for specific feathers, colors, chirps, and ostentatious behaviors to choose their mates, thereby driving the evolution of sexually-related decorative organs. Prum called this evolutionary process, driven by the sensory judgments and cognitive choices of biological individuals, "aesthetic evolution."
This was not Prum's first, he simply stood firmly with Darwin's theory of sexual choice.
In a letter to the American biologist Asa Gray, Darwin said: "Whenever you stare at a feather on a peacock's tail, it will make my head as big as a bucket." This extremely complex, cumbersome form made Darwin realize that this was an evolutionary problem that was difficult to explain by natural selection.
In The Origin of Man and Sexual Selection, In addition to natural selection, Darwin proposed a purely aesthetically influenced mate selection made primarily by females, that is, the theory of sexual selection.
However, Wallace, the co-founder of the theory of evolution, and his successors suppressed the theory for nearly a century. Darwin's theory of sexual selection meant that animals also had strong emotions, keen intuition, and the ability to appreciate beauty, which was absurd to Wallace.
As a scientist with more than 40 years of bird watching experience and 30 years of study of bird evolution, Prüm's boldness lies not only in his eagerness to reverse the fact that Darwin's theory of sexual selection has been marginalized, but also in an attempt to push it to another extreme—the subjective aesthetic experience of animals has a crucial and decisive influence on the evolutionary process.
If he has always been opposed to the monolithic theory of evolutionary dynamics, then his slightly radical desire to place sexual choice in a new mainstream position seems to be suspected of overcorrection.
Perhaps, this is why his popular science book "The Evolution of Beauty" has not received much support in the field of evolutionary biology, although it has sold well in the United States and has been nominated for the Pulitzer Prize in the United States.
Are sexual selection and natural selection mutually exclusive?
At the beginning of the birth of sexual selection theory, natural selection was "incompatible" with it. British scholar Helena Cronin explained in her book Ants and Peacocks: The Battle of Sexual Selection Behind The Dazzling Feathers that sexual selection is driven by female preferences that lead to competition between males of the same species; the standard force of natural selection is between species, not within species and within society. Sexual selection is purely related to mating success; in contrast, natural selection, success and failure cover a fairly wide range of matters – survival and all reproductive matters other than mating. "This gap is significant, it is tantamount to digging a gap between sexual selection and natural selection."
But Wallace also doesn't really completely rule out female choice. Later, he offered a new interpretation of female selection, arguing that the beauty of female preferences was not pure, that those seemingly useless features might suggest certain useful qualities, such as vitality, health, or perseverance, and that the essence of female selection became the pursuit of good qualities, which was very similar to the results of natural selection. Therefore, in any case, sexual selection is only an appendage of natural selection.
The example of the Australian flower pavilion bird can explain this statement. Males have the habit of building pavilion-like buildings and decorating them with petals, and females come over to examine their work and then mate. The pavilion building does not serve any other purpose. Scientists once found in an ornament experiment that the probability of male birds mating success depends on the quality of the ornament, especially the number of snail shells and blue feathers in the pavilion. This seems to mean that the choice of the female is to rely on beauty.
However, there is also an indicator: the male will try to damage the pavilions of other males, and their ornaments are partially stolen from the building materials of other male birds. Therefore, the degree of decoration of the male bird's pavilion also reflects the male's ability to defend his own pavilion and steal the property of competitors, which can represent certain useful qualities, such as strength, endurance, and secret action. In fact, the fighting nature of the flower pavilion birds in building the pavilion is indeed directly proportional to the dominant position of the male birds in the group.
Liu Yang, an associate professor of zoology at Sun Yat-sen University, added that the theories of evolutionary biologists Hamilton and Zucker suggest that some traits about beauty can show that the ability of courtship to resist parasites and diseases is actually related to individual quality.
There are many more such cases in nature. Zhou Zhonghe, an academician of the Chinese Academy of Sciences and a paleontologist, said that it illustrates a difficult problem, and many times, the role of sexual selection and the role of natural selection are difficult to distinguish. It is difficult to prove that "beauty is only for beauty" is difficult to prove.
Liu Yang told China Science Daily that one of the reasons Prume's idea has been controversial in the Western evolutionary biology community is that his evidence has a clear subjective tendency, and he does not tell readers about the obvious and clear evidence of natural selection at the same time, and such scientific interpretation is not balanced enough.
In fact, since the 1980s, he said, sexual selection has begun to receive attention from evolutionary biology and is less passive, thanks to the "Fisher out of control process" theory.
For example, Fisher hypothesized that there was a male with slightly longer tail feathers at first because it helped to fly, which was the result of natural selection, but then this feature became a source of attraction. If a female chooses a mate with a longer tail, her sons will most likely inherit this trait. If other females in the colony also prefer to have long tails, it will eventually have more offspring because its sons are more favored by females. As a result, this trait and the genes that prefer it will co-evolve and self-reinforce.
This suggests that female choices originate from rational adaptation before breaking up with this practicality.
Three American scientists engaged in sexual selection research published a lengthy book review in the academic journal Evolution, and they believe that in Prum's view, beauty and adaptive values are seen as completely incompatible, but the "Fisher out-of-control process" is not as different from adaptive evolution as he thinks. "Mutual exclusion only marginalizes the contribution of sexual selection to evolution."
Evolutionary biology today holds that sexual selection and natural selection are not completely separated, and that the gap between them is narrowing.
Underrated sexual choice
In fact, Darwin has long understood that if he put forward the concept of animal "aesthetics", implying that females have the ability to choose and taste, it will inevitably lead to denial. An important reason is what Cronin calls the fear of "anthropomorphism." Anthropomorphism refers to the inappropriate imposition of human attributes on other animals. But she argues that the theory of sexual selection is not about "recognizable animals," but about "genes that have the ability to recognize."
On the contrary, much of the controversy against Prum is that he uses aesthetic evolutionary theory to explore human courtship choices, the evolution of sexual behavior, and even the so-called "sexual autonomy" in animals as a moral guide for human society.
Jerry Coyne, a prominent evolutionary biologist at the University of Chicago, expressed his antipathy to this practice in his comments, that female selection in birds is a direct product of evolution, and that the free pursuit of human women is the rational conclusion that humans improve society by treating each individual equally. He argues that it is not advisable to present a theory to the public in a misleading way.
However, the value of "The Evolution of Beauty" is that it has once again set off an enlightening thinking in the academic community and even the public about the neglected theory of sexual choice. As Zhou Zhonghe said, the contribution of sexual selection to biological evolution is underestimated, and it is worth doing more open-ended research to help us explore the dynamics of evolution in nature.
In fact, Liu Yang specifically mentioned that as a popular science book, "The Evolution of Beauty" has been published less than a year ago, and has received nearly 60 academic citations, which has caused heated discussion in the academic community, making the study of the dynamics of sexual selection a hot topic in recent years.
"Perhaps the publication of this book will inspire more thoughtful researchers to use different research methods to explore key scientific issues in the field of sexual selection." Every scientific point of view needs to be confirmed or falsified, so that fresh ideas and scientific results will continue to emerge. In any case, the phenomena and theories related to sexual selection are fascinating areas in evolutionary biology and behavioral ecology. Liu Yang added.
Moreover, Prume's brilliance lies in his passionate description of the beauty of nature. Prüm's focus on beauty and aesthetics was unanimously appreciated because it required great courage. As three american scientists engaged in sexual selection research believe, exploring the open relationship between evolutionary biology and art, aesthetics, psychology, and philosophy is very affirmative and promising.