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"Sexual dimorphism" is the scientific term for physical differences between males and females of a species. Many extreme examples exist: Peacocks far outclass peahens, for instance, while female anglerfish both outsize and outwit their tiny, rudimentary, parasitic male counterparts.
Unlike those animals, men and women are more physically similar than we are different. Nonetheless, there are a few key distinctions in our physiques. Some of them are designed to suit each sex for the role it plays in reproduction, while others exist to help us tell each other apart and to aid in our mutual attraction.
Breasts vs. chestsSlide 2 of 13
Breasts vs. chests
Women have breasts, whereas men have flat chests (but still with nipples on them). Why?
Women are the only primates who are busty all the time, even when they aren't nursing. Alternative theories exist, but most scientists think breasts are an evolutionary trick for snagging men; though they're actually filled with fat, not milk, they signal a woman's bountiful ability to feed her children.
Breasts also help men figure out who to pursue to achieve reproductive success. Prepubescent girls don't have breasts, and the breasts of post-menopausal women are often shrunken and saggy . A full, buoyant bosom can therefore demonstrate fertility.
Men aren't trying to trick women into thinking they can breastfeed, so they don't have breasts. They do, however, have nipples: This is because the genes that code for nipple development switch on in utero, and at a very early embryonic stage even before the genes gear up that turn us into males or females.Slide 3 of 13
Big apple vs. smallSlide 4 of 13
Big apple vs. small
Men and women both have cartilage surrounding their voice boxes, but because men have bigger boxes (which give them deeper voices), their chunks of cartilage protrude more. This gives them neck lumps called Adam's apples.
But why do men have deeper voices than women? The answer is that the pitch of a man's voice correlates with the amount of the male sex hormone testosterone he has, and his testosterone level is itself indicative of his genetic quality and sexual fitness. Because women have evolved to seek out men who have all the indicators of fitness and health, studies have shown time and time again that women tend to be more attracted to men with lower-pitched voices. They're looking for a mate with whom to produce healthy offspring.Slide 5 of 13
Square vs. heart-shaped facesSlide 6 of 13
Square vs. heart-shaped faces
The more testosterone a man has, the stronger his brow, cheekbones and jaw line. Meanwhile, the more estrogen a woman has, the wider her face, fuller her lips and the higher her eyebrows. In short, sex hormones control the divergence of male and female facial features.
Along with chiseled jaws, higher testosterone has been shown to correlate with muscle strength and aggression in men, as well as with genetic vigor. Perhaps for this reason, studies have shown that women judge men with more angular features as likely to be dominant over men with rounder, more effeminate faces.
They also tend to rate men with masculine features as more attractive, especially when they themselves are ovulating and, thus (at least subconsciously) on the lookout for a male sex partner who'll produce fit offspring. When they're looking for a long-term partner, on the other hand, studies show that women tend to prefer men with more effeminate features, who have less testosterone and are likely to be more loyal partners and caring fathers. [How Women Pick Mates vs. Flings]Slide 7 of 13
Hairy vs. notSlide 8 of 13