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Human men and women are sexually dimorphic: there are some phenotypic differences between men and women. Men being taller than women is an accurate stereotype. Overall, men are on average 13 centimeters taller than women. The most extreme example is Macedonia, where the average man is 18.5 cm taller than the average woman.

When you look at animals, I think it's pretty intuitive to think that females are often larger than males from the same species. Spiders, fish, insects, some birds, there's an endless list of examples of bigger females than males. This is explained by a variety of different reasons depending on the species, from mate competition to the ability to bear children. So why would human males be so much bigger than women?

We all know that there are a lot of factors behind the height - and, on a related subject, strength - differences between the sexes. There are some genetic factors, as pointed out in this interesting Quora post about the topic. We also know that nutrition has a large impact in growth. In a word, we know what causes the height difference between men and women. There is a great post about it here. But I couldn't find any conclusive evidence as to why men are taller than women.

Is this because women naturally like tall men? Did prehistoric men have to be taller than women in order to thrive? Or is it just genetic drifting that, more or less randomly, led to this height difference?

The motivation behind my curiosity is feelings-driven. A while ago, my dad said during a conversation that he once "saw a documentary in which they explained that early men stole all the good proteins from the women, so they could grow taller and stronger unlike the poor females." As much as I love and respect my dad, I have a hard time believing that men are natural culprits and thieves. I am by no way making this post just to "prove him wrong" - I am absolutely interested by the topic and would love to know more. Also, if anyone knows the documentary he was talking about, I would be glad to give it a watch.

All apologies for any bad English you might find. Please tell me if I make recurring grammar mistakes.

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    $\begingroup$ In many mammalian species, the male is larger than the female. It is not a special case in humans. $\endgroup$
    – WYSIWYG
    Jul 19, 2019 at 10:06

2 Answers 2

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I assume by asking why, you are asking about the distal evolutionary causes, and not the molecular mechanisms that account for these things.

(Important disclaimer: these causes are difficult to be certain about; they require a fair amount of informed speculation.)

With that said: it is widely agreed upon in evolutionary biology that human males, as in other mammals, are thought to be larger mostly due to sexual selection. In other words, size is sexy, and sexy individuals fare better with respect to mate choice, on average. Sexual selection can also work via male-male competition. There may be other causes that are relatively minor contributors compared to this one.

Notice, however, that in humans, females evidently do not remain tiny with respect to males, but they get 'dragged along' in terms of their height, so that males are not drastically different in height (unlike, for instance, in elephant seals). This too may be a result of sexual selection, quirks of physiology across the sexes (e.g. genetics of dimorphism), or even natural selection. Think hip size and the size of human skulls.

Additionally, differences in development time (e.g. length and onset of puberty) can skew body size. Humans certainly exhibit dimorphism with respect to development.

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  • $\begingroup$ Thank you for this very interesting answer. Indeed, my question was about distal evolutionary causes, and not molecular things. The example of the elephant seal is great, I was not familiar with this. I can't vote on your answer due to low rep but I greatly appreciate it. $\endgroup$
    – C. Crt
    Jul 19, 2019 at 11:00
  • $\begingroup$ Women do not get dragged along, more extreme sexual dimorphism exists in other great apes. Differences in sexual dimorphism is well predicted by levels of competition and cooperation. $\endgroup$
    – John
    Aug 24, 2019 at 17:44
  • $\begingroup$ Sexual selection isn't an arbitrary process, it's generally based on objective evolutionary qualities. So shouldn't it rather be: Size is better, so size is sexy. But then this answer is really missing the point? $\endgroup$
    – Alex
    Jan 30, 2021 at 11:15
  • $\begingroup$ Certainly sexual selection can be a completely arbitrary process and in many (in many clades, most) species it is completely arbitrary and devoid of any real hallmark of signal of fitness. Sometimes, things just become sexy and this drives traits for that sexiness to be selected, and it often also sometimes drives species to extinction due to the trait rendering individuals unfit for competition in their habitats. Beetle weaponry and bird coloration and generally all sorts of ornamentations come to mind. $\endgroup$
    – S Pr
    Feb 2, 2021 at 12:24
  • $\begingroup$ Sexual selection would explain tall people. But it doesn't explain taller MEN. Because the same tall men would produce both sons and daughters. Unless the argument is that tall men would produce more sons (e.g. the children of Presidents of the United States), while short men produce more daughters. $\endgroup$
    – Tom Au
    Jan 9, 2022 at 5:29
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More details to support @SPr's answer, from the abstract of Plavcan (2012): "Sexual Size Dimorphism, Canine Dimorphism, and Male-Male Competition in Primates: Where Do Humans Fit In?"

While dimorphism in primates is associated with agonistic male mate competition, a variety of factors can affect male and female size, and thereby dimorphism. The causes of human sexual size dimorphism are uncertain, and could involve several non-mutually-exclusive mechanisms, such as mate competition, resource competition, intergroup violence, and female choice. A phylogenetic reconstruction of the evolution of dimorphism, including fossil hominins, indicates that the modern human condition is derived. This suggests that at least some behavioral similarities with Pan associated with dimorphism may have arisen independently, and not directly from a common ancestor.

  • mate competition: bigger males can beat up smaller males to gain access to females
  • resource competition: bigger males can beat up smaller males to gain access to resources (and hence survive better/gain access to females/have their offspring survive better/etc.)
  • intergroup violence: bigger males are more likely to survive & win when fighting with smaller males in other groups
  • female choice: as @SPr says: "size is sexy, and sexy individuals fare better with respect to mate choice, on average"

And "the modern human condition is derived": that means that our best guess is that human dimorphism and behaviour have evolved since we split off from the rest of the primates; this makes it slightly harder to use non-human primates as a model.

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