Many species, including primates, exhibit varying degrees of sexual dimorphism, which refers to the physical differences between males and females that do not pertain to reproduction. A prominent example is size; male gorillas are approximately twice the weight of their female counterparts, while female stingrays can be up to three times larger than males. In humans, males generally have greater height and upper body strength, demonstrating about 15% dimorphism. Interestingly, around 10% of women surpass the average male in height, and some women can outmatch men in strength.

Height is influenced by numerous factors, including genetics and consistent access to nutrition. "Today's average young adult is approximately 8 to 9 cm, or about 5%, taller than their ancestors from a century ago. The changes in average height have varied between genders across different countries. For instance, in South Korea, women's mean height increased by 14%, while men's grew by 9%. Conversely, in the Philippines, males saw an increase of about 5%, while females only grew by 1%." (source)

It has been suggested that men's greater height serves an evolutionary advantage related to mate competition, a notion supported by Charles Darwin.

> “There can be little doubt that the greater size and strength of man, in comparison with woman, together with his broader shoulders, more developed muscles, rugged outline of body, his greater courage and pugnacity … have been preserved or even augmented during the long ages of man’s savagery, by the success of the strongest and boldest men, both in the general struggle for life and in their contests for wives,” he posited in The Descent of Man. (source)

This aligns with Darwin's belief that male sexual behavior is naturally promiscuous, while females are more selective. Although this narrative seems plausible when considering the natural world through a Victorian lens, it fails to hold up under scientific scrutiny. Female primates, for instance, are far from being coy or selective in their mating.

> "In fact, female primates couldn't be further from reluctant breeders or seekers of 'intimacy' with a single 'best' mate, or dead set on mating with 'the alpha.' Indeed, (primatologist Meredith) Small suggests that it is difficult for us humans to wrap our minds around 'just how little importance nonhuman female primates attach to knowing a male before they mate with him.'"

> Martin, Wednesday. Untrue (pp. 164–165). Little, Brown and Company. Kindle Edition.

Both animals and humans can gain evolutionary benefits from sexual promiscuity. "A female who mates with various males increases the genetic diversity of her offspring, enhancing the odds that some will survive." (source) Moreover, there are circumstances when it is evolutionarily beneficial for males to be selective as well. (I have explored these myths in previous writings; one can be found at the bottom of the page.)

It is overly simplistic to claim that all human mating follows a rigid set of rules, as mating strategies are heavily influenced by context. A group of researchers debunking the "Bateman Paradigm," which supposedly validated Darwin's theory of binary sexual roles, stated: "We argue that human mating strategies are unlikely to conform to a single universal pattern."

Furthermore, humans evolved as multi-maters rather than competing physically like elks or gorillas. The coronal ridge on the human penis is designed to remove semen left by other males, which would not be necessary if such competition occurred prior to mating. Consequently, men typically become flaccid after ejaculation and require a refractory period before they can engage again.

The human cervix functions similarly to that of some primates, assessing sperm quality. "For the human female cervix, like that of a promiscuous macaque who may breed with ten males or more in rapid succession, actually serves not so much to block sperm, as was previously believed, as to busily filter and assess it, ideally several different types of it from several different males, simultaneously. It evolved not as a simple barrier but to sort the weak and bad and incompatible sperm from the good, suggesting by its very presence that there was a need to do such a thing — i.e., that females were mating multiply."

> Martin, Wednesday. Untrue (p. 145). Little, Brown and Company. Kindle Edition.

Our biological makeup reflects that we are designed for multiple mating, and early humans likely did not engage in frequent physical confrontations over mates—there was simply no need. In a communal environment where food is shared and individuals care for each other, the identity of a child's father becomes less significant. As noted by primatologist Frans de Waal, "When group stability is important for individual advantage, selection will favor active peacemaking and cooperation in our closest relatives and ourselves." (source)

Moreover, constant conflict would have been detrimental to the survival of the group. Life during the Paleolithic era was already fraught with challenges, and infighting among tribe members would have threatened their collective survival.

If men had evolved to be larger and stronger due to domination and mate competition, we would expect that no women would exceed the average man in height or strength. However, this is not the case, leading us to question the motivations behind male size.

The answer lies in one word: Estrogen.

> Ovaries are significant because they produce significantly more estrogen than testes, and this hormone plays a crucial role in bone development. "In all human skeletons, a lot of estrogen stimulates long bone growth," Dunsworth explained. Before puberty, individuals with ovaries and testes grow at roughly the same rate. Afterward, those with ovaries see a surge in estrogen production, which activates the growth plates in their bones, leading to longer long bones. This explains why, during early adolescence, girls are typically taller than boys.

However, this growth surge is temporary, as elevated estrogen levels cause the growth plates to fuse. This is why height varies between genders: individuals with ovaries reach their peak in estrogen shortly after puberty, as their ovaries begin regular monthly cycles. In contrast, the bones of those with testes continue to grow for several more years until their estrogen levels peak, resulting in taller stature. (source)

Although the theory connecting estrogen to sexual dimorphism is not new, it has often been overshadowed by an uncritical emphasis on sexual selection. While social anthropologists generally believe that inter-male competition was low during the Pleistocene (source), the enduring notion of male competition aligns well with modern hierarchical beliefs. There is substantial evidence supporting cooperation as a key factor in early human evolution, yet patriarchal narratives persistently try to validate themselves with stories that present such competition as timeless.

Additionally, for much of history, male bodies were regarded as the "default" in scientific research, leading to the under-exploration of female physiology. This has further entrenched the belief that sexual selection, rather than estrogen, is responsible for size differences in humans. People often see and believe what aligns with their biases.

> "Not only have doctors, scientists, and researchers mostly been men, but the majority of cells, animals, and humans studied in medical science have also been male: most medical advancements have arisen from the study of male biology. Dr. Janine Austin Clayton, an associate director for women’s health research at the United States National Institutes of Health (NIH), stated to the New York Times that the outcome is: 'We literally know less about every aspect of female biology compared to male biology.'" (source)

However, this is beginning to change. Physiology, endocrinology, and bone growth are all evolutionary factors, not merely social constructs. Examining the timing of human puberty provides insight into how and why estrogen affects average height differences.

> "In virtually all other species, including great apes, puberty occurs as growth is tapering off. While males may gain some weight, there is no notable change in skeletal size at puberty (Bogin, 1999). Some researchers propose that the pubertal growth spurt is a delayed catch-up growth, occurring only after brain growth is largely completed to safeguard the brain's nutrient competition." (source)

In essence, humans continue to grow post-puberty in a manner not typical of other primates. The significant rises in estrogen in those with ovaries lead first to a growth spurt and then to the fusing of growth plates, a process that males do not experience due to much lower estrogen levels. This phenomenon stems from other evolutionary mechanisms rather than aggressive sexual selection processes—an assumption made without consulting social anthropologists who specialize in pre-history, likely because it fits within contemporary social dynamics. Moreover, the historical exclusion of women from scientific consideration has compounded these misconceptions.

> "We need much more evidence than just the existence of body size differences in and of themselves," remarked Louise Barrett, an evolutionary anthropologist at the University of Lethbridge, who co-authored a 2016 review paper on the evolution of human height variation with Gert Stulp of the London School of Hygiene and Tropical Medicine. The sexual selection hypothesis may seem intuitive—scientists rationalized that "men are bigger than women, and men like to fight a lot, so those two things must be connected," Barrett explained—but it does not align well with rigorous research. "The studies aren’t particularly good."

> "We require more precise or rigorous testing of evolutionary hypotheses overall, and especially concerning humans," Barrett emphasized. "Our self-perception influences our behavior and actions. It is crucial to possess an accurate representation." (source)

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