Sexual Drive and the Evolution of Humanity


Published in the Philosophical Review, 2023


Book Review :  “The Evolution of Beauty:

How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World, and Us

by Richard O. Prum


Following the discovery of the generic code in mid-20th century, anticipation for a deeper insight into evolutionary biology sharply rose among scientists. Comparing the genetic map of various animals, however, presented an unexpected result:

Humans and chimps share a surprising 98.8 percent of their DNA. How can we be so similar–and yet so different?

– a question difficult to answer (American Museum of National History, 2023).

Despite that apes share with people the same genetic patterns, and the same physiological and emotional functions, yet the outlook appearance of humans and apes is dramatically different. How can the process of adaptation and Natural Selection explain this outstanding difference between species?

In his book, The Evolution of Beauty, Prof. Richard O. Prum argues that examples exist of certain developments in evolution, which cannot be explained by Natural Selection alone. Natural Selection was suggested by Darwin in his first book: On the Origin of Species, (1859), a book which created an earthquake in the domain of humanity’s thoughts about its origin. Yet, the aftershocks were still to appear in response to his second book The Descent of Man, and Selection in Relation to Sex (1871).

It was so difficult for people during the conservative atmosphere of the 19th century to accept even Natural Selection, let alone to consider another mechanism of evolution in which Sexual Selection (or ‘mate choice’) was suggested. It took about one hundred years for evolutionary biologists to seriously consider ‘mate choice’ as a genuine mechanism in the process of evolution.

Sexual Selection Motivated by the Sense of Beauty

While scientific studies focus on the objective aspects of observed phenomena, introducing the subjective element of “beauty” in the study of evolution may seem unusual. Darwin’s courage and broadmindedness, however, led him to freely suggest that animals' sense of beauty has an impact on their evolution:

The most notable and revolutionary feature of Darwin’s theory of mate choice is that it was explicitly aesthetic. He described the revolutionary origin of beauty in nature as a consequence of the fact that animals had evolved to be ‘beautiful to themselves’ … What was so radical about this idea was that it positioned organisms – especially female organisms – as active agents in the evolution of their own species … Unlike natural selection, which emerges from external forces in nature, such as competition, predation, climate and geography, acting on the organism, sexual selection is a potentially independent, self-directed process in which the organisms themselves (mostly female) were in charge” (Prum, 2018, pp. 23-24).

The traits that attract a female bird, for example, in mate choice are visibly encoded in ornaments and colours displayed by male partner, presenting them like his ‘profile’ for mating. In this process, beauty is desirable

“… because it brings real world benefits, like vigour, health, or good genes” (p. 11).

Detailed account of various kinds of animals mating rituals were described in prof. Prum’s book, outlining the observation of animals feeling and desire for beauty:

“Darwin described females as having a taste for the beautiful and an aesthetic faculty. He described males as trying to charm their mates: With the great majority of animals … the taste for the beautiful is confined to the attraction of the opposite sex. The sweet strains poured forth by many male birds during the season of love are certainly admired by the females… If female birds had been incapable of appreciating the beautiful colours, the ornaments and voices of their male partner, all the labour and anxiety by the later in displaying their charms before the females would have been thrown away, and this is impossible to admit” (p. 24).

Describing how the ritual of Sexual Selection worked in the animal world, Prof. Prum explains further that Darwin presented the impact of this evolutionary mechanism on our emergence as human beings – so similar yet also different from other apes:

From furless bodies to the enormous geographic, ethnic and tribal diversity in human appearance, to our highly social character, to language and music, Darwin made a powerful case that sexual selection had played a crucial role in the shaping of the human species (p. 22).

Females-Led Evolution

Perhaps a mother-to-be is motivated by a conscious drive not only for her own self-protection but for securing the future of her offspring. This drive leads her to a serious evaluation with whom to mate. Through this perspective, the traits of future generations become decided by mothers-to-be. Prof. Prum explains why his book is focused on the role of females in shaping the future generation of species:

“If female aesthetic preferences drove the process, then female sexual desire was responsible for creating, defining, and shaping the most extreme forms of sexual display that we see in nature. Ultimately, it is female sexual autonomy that is predominantly responsible for the evolution of natural beauty. This was a very unsettling concept in Darwin’s time – as it is to many today …

Sexual autonomy is the capacity for an individual organism to exercise an informed, independent, and uncoerced sexual choice with whom to mate with … In ‘Descent’, Darwin presented his hypothesis that female sexual autonomy – the taste for the beautiful – is an independent and transformative evolutionary force in the history of life” (p. 27-28).

Unlike the process of Natural Selection, governed by merciless forces of the environment, the element of pleasure is central to Sexual Selection:

“Viewing pleasure as the central, organising force in mate choice, and mate choice as a major dynamic in evolutionary change, the aesthetic theory holds that women’s pursuit of pleasure is at the very heart of the evolution of human beauty and sexuality” (p. 264).

In other words, female urge for motherhood is absolute, an end on itself:

Female sexual pleasure and orgasm are the evolutionary consequences of female desire and choice, and they are ends unto themselves” (p. 274).

The Evolutionary Shift Towards Humanity

In the social life of many primate species, a conflict of interest between genders is evident. Females make all the reproductive investment required for raising the young, while males invest exclusively in seeking hierarchy and domination, enabling them to exploit sexual opportunities. But even after the fight for domination, violently deposing the previous dominant male, the new ‘top guy’, as the book explains, cannot immediately capitalise on his reproductive opportunities, because females are either pregnant or breast-feeding dependent young, and this lengthy process suppresses ovulation – and female cannot mate:

Consequently, males of many primate species have evolved to create new reproductive opportunities for themselves by killing all the dependent offspring of females when they gain control of the group. When a female’s dependent child is killed, the fact that she is no longer breast-feeding will cause her to go into estrous, at which point she will resume mating. Infanticide is a selfish male solution on how to capitalise quickly on the advantages of having won male-male competition” (p. 285).

This ‘tradition’ in apes-male violence is devastating for females. Infanticide is a sexual threat that also endangers the reproductive opportunities of the female, given the limited time of motherhood ability.

A shift in this situation of sexual conflict could only take place by courageous females resisting sexual coercion and attracting less violent males. Females could exercise mate choice for their benefit:

“Male infanticide accounts for 38 percent of infant deaths in baboon and 33 percent in gorillas. What is common male monkey and ape behaviour is almost unknown in any human society. Even through men are still responsible for the overwhelming majority of human violence, human males do not murder young children for their reproductive benefit. (p. 289).   “An evolutionary solution to the infanticide problem was absolutely essential for the evolution of human biology” (p. 290).

Rejecting violent males through Sexual Selection led also to ‘de-weaponizing’ violent males' canine teeth, which are blade-sharp in gorillas and chimpanzees, and this reflected on gentler face muscles in future generation:

“Reduction of male weapons would decrease the efficiency of male coercion and infanticide. Females that prefer males with smaller canines would receive the indirect, genetic benefits of having attractive offspring …. The result is an aesthetic expansion of female social and sexual autonomy “(p. 297).

Having Sexual Selection working for their benefit, female choice expanded from the immediately perceivable physical features of potential males to encompass the broader social personality and social relationship. Unlike other apes whose males do not show any interest in caring about their young, men share in the extended period of child development and in substantial ongoing parental investment – the book further explains. To please choosy females and thereby gain enduring sexual access, male engaged in parental investment of food, protection and cooperation that come with the pair bond:

I think a very powerful case can be made for the role of female mate choice in the evolution of the human species” (p. 302).

Attraction to Beauty

While male birds are devoted to developing ornaments and extreme colours to gain the chance to mate, in emerging human society it was men who were attracted to women’s beauty and ornaments:   

Until now, we’ve looked mainly at female mating preferences for male display traits, because in the birds we’ve discussed it is the females who are the drivers of sexual selection and the evolution of extreme beauty. But it’s clear that in humans both sexes are involved in mate choice … Darwin proposed that nearly naked human skin – the evolutionary reduction in body hair – evolved as a sexually selected aesthetic trait…. It’s clear that another [trait] – the retention of specialised patches of hair in the armpit, pubic region, scalp and eyebrows – is ornamental. The hypothesis that underarm and pubic hair are evolved sexual signals [in both genders] is further supported by the observation that these patches of hair do not develop until puberty “(p. 252-253).

The outstanding female body shape evolution was not natural-selection-induced but was the result of male sexual preferences:

“The ‘Beauty Happens’ hypothesis proposes that human female sexual ornaments – like permanent breast tissues and the enhanced curves of the hip and buttocks – have arbitrarily coevolved with male sexual preferences for them” (p. 258).

With both genders exercising Sexual Selection, a sharp break and a huge shift occurred distancing us from our primate ancestors.

The Inwardly Driven Evolution

This fascinating book leads us to ponder about the philosophical impact of Sexual Selection on the process of gene delivery and hence on shaping future generation of our humanity. The mechanism of Natural Selection focuses on external influences affecting the survival of individuals, while Sexual Selection is based on the individual’s subjective preference and motivation. The implication of both couples applying the mental power of evaluation and choice – is that Evolution was not a blind process based only on environmental forces described by Natural Selection. Sexual Selection is the decisive mechanism for the delivery of genetic information to the next generation, information which encodes ancestors' conscious preferences:

 “As Darwin hypothesised, with the evolution of sensory evaluation and choice comes the emergence of a new evolutionary agency – the capacity of the individual judgements to drive the evolutionary process itself. Aesthetic evolution means that animals are aesthetic agents who play a role in their own evolution” (p. 324).

In other words, it seems that individuals were using their own impressions and intelligence to design the destiny of future generation. It is like an “intelligent design from within the species” – using already available mental and physical resources and biological capacity – and improving on them.

Sexual Selection expresses the urge for ‘better future survival’ – implying that engaged individuals are aware not only of the immediate result of sexual encounter, but have exercised mental evaluation and prediction of latent effects.

When we look at ourselves in a mirror, we should appreciate the hard work of uncounted sexual encounters over the past 2 million years that led us to our current appearance.



-  American Museum of National History. (2023). DNA: Comparing Humans and Chimps. 

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

-  Darwin, C. (1871). The Descent of Man, and Selection in Relation to Sex. John Murray.

-  Prum, R. O. (2018). The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World-and Us. Google Books. pp. 11-324.