A look at the genitals: Human men have disproportionately large genitals – you penis is far larger than that of similar-sized great apes. But why? Researchers now have this all in one experiment examined.

They wanted to know: Were women the driving force because they prefer men with larger penises? Or did our ancestors perhaps use their oversized bodies to intimidate rivals?

Researchers examined the human male’s genitals

It is a mystery of evolution: among all primates is the Human men’s penis an outlier: in relation to his body size, he is exceptionally fat and tall. But why? It stands to reason that there was an evolutionary effect at work here – a selection pressure that gave our early male ancestors an advantage if they had larger penises. Because unlike today, the genitals were not covered by clothing back then.

But what selective effect is behind the disproportionate size of human men? “There are two main mechanisms for sexual selection in male animals,” explain Upama Aich from the University of Western Australia and her colleagues.

“On the one hand, the females’ choice of partners can lead to certain characteristics of the males that are considered attractive becoming more noticeable.” On the other hand, a trait can also be strengthened if it serves to deter male rivals.

Subjects rated computer-generated images of male figures

To find out what effect works on us humans, Aich and her team conducted an experiment with 600 men and 200 women. They showed the test subjects 56 computer-generated, life-sized male figures that differed in three characteristics: body size, the size of the penis when at rest and body stature – from broad-shouldered and narrow-hipped to more pear-shaped body shapes.

The task for the female test subjects was: “State how sexually attractive you find this man on a seven-point scale.” The male participants were given two questions. The first: “How jealous would you be if this man talked to your partner?” The second question was, “How threatened would you feel if this man tried to fight you?”

What was most important to women

The experiment showed that women actually prefer men with larger penises – but not under all circumstances. “Linear selection was strongest for male stature, followed by weaker but still significant preferences for height and Penis size“, report Aich and her team. If a man was short and visibly not fit, a larger genitalia did not bring him any particular advantages in terms of attractiveness.

However, women’s preference for tall, fit men with large penises has clear limits – bigger is not infinitely better. Above a certain value, having even larger genitals or even broader shoulders no longer brought any attractiveness advantages. Instead, the preference curve of the female test subjects reached a plateau, as the evaluations showed.

Men overestimate the importance of characteristics when choosing a partner

This was different for the male test subjects. They also rated exaggerated features such as an extreme V-back or an unrealistically large penis as an advantage in women, as the jealousy question showed.

“This suggests that men tend to overestimate the importance of these characteristics for female partner choice,” explain Aich and her team. “This distorts their perception of competition from attractive rivals.”

Penis size influences assessment of rival’s fighting strength

But even more interesting were the men’s answers to the question about perceived threat: “In our opinion, the most important result of the study is that penis size influences how men assess the fighting strength of a rival,” the team wrote. “Men felt more threatened when a potential opponent had a large penis.”

“This provides the first experimental evidence that penis size in humans is also under sexual selection pressure because it is perceived as a signal of fighting strength,” the researchers state.

In their opinion, there could be a biological basis for this. Because testosterone levels influence how much a boy’s genitals grow during puberty. But high testosterone levels also promote muscle growth and aggression – and thus dangerousness in combat.

Two factors caused the growth of the limb

But what does this teach us? According to Aich and her colleagues, the disproportionately large member of human men could have arisen from two complementary selection forces. “Our results suggest that both female preferences and competition with other men promoted the increase in genital size,” explain the researchers. The same selection pressures may also have given advantages to taller men with broad shoulders.

“However, it is also important to note that human choice of partner is strongly influenced by cultural norms and the environment,” emphasizes the team. However, the extent to which this was similar for our ancestors is unknown. In addition: “It is entirely conceivable that the effect of limb size on sexual stimulation also played a role,” explain Aich and her team. This so-called post-copulatory selection could have further strengthened the preferences.