The bones in a man’s face are thickest in exactly the places a fist lands. The jaw, the cheekbones and the brow are reinforced. A woman’s face is not. The researchers who mapped it concluded that fists evolved to fit faces, and faces evolved to take them.
That is the record of a contest. Men fought, the men with stronger faces won, and their sons inherited the face. Every part of a man’s body carries a record like this, and inside a single lifetime those records have started to fade.
Men Contest Men
Men contest other men over who throws hardest, who fights best, who makes the finest tool and whose voice carries furthest. The contest ranks men from the center to the edge. Women read the result. Her attraction fires on the markers of the winners as automatically as his drive to compete.
Birds show the pattern plainly. On a lek, males gather on one patch of ground and compete for the center. Females walk through and settle on the center, so ten to twenty percent of the males get most of the matings. Humans ran the same tournament for hundreds of thousands of years, and the winners passed on the body that won it.
What Is Sexual Dimorphism?
Sexual dimorphism is the difference in body and mind between the males and females of one species. A stag’s antlers, a silverback’s bulk and a man’s jaw all count.
Stand a man and a woman side by side and compare shoulders, hips, height, jaw and voice. Biologists call these two forms of one species sexual dimorphism. Each difference works like a fossil record of the contest that built it.
How Dimorphic Are Humans?
A male gorilla weighs about twice what a female does. Male and female gibbons are close to the same size. On a scale, men land in between, about fifteen percent heavier than women.
The scale hides most of the gap. Women carry more fat, and fat evens out the weight. Muscle shows it. Men carry about sixty percent more muscle than women and over seventy percent more in the arms, and a man’s upper body is roughly ninety percent stronger. That upper-body gap comes close to the weight gap between a silverback and his females.
So humans don’t sit at the gibbon end. Where the contest selected hardest, in the arms, shoulders and hands, the difference between the sexes is large.
Sexual Dimorphism in Humans: Shoulders, Hands, Face, Voice
Height comes first. American men average about 5 foot 9 and women about 5 foot 4.
A man’s shoulders are far wider than a woman’s and his waist is narrower. That V is a lever for throwing overhand. The full throwing build appears in Homo erectus almost two million years ago, alongside piles of throwing stones. Men threw at prey and at each other, and a man’s upper body is nearly twice as strong as a woman’s.
The hands record gripping, wrestling and tool use. In one military study, nine in ten women gripped weaker than ninety-five percent of the men.
The face records fighting. The bone is armored where the fist lands, and in impact tests a beard absorbed more of the blow before the bone broke.
The voice records the fight for rank. Human males have the largest gap in voice pitch of any ape, almost an octave below women. A red deer stag’s voice drops the same way, and he uses it to roar down rivals.
Testosterone builds all of these traits. When that signal drops, the records fade with it.
The Signal Turned Down
Three separate measurements show it dropping. Testosterone in American men has fallen about one percent a year, beyond anything age explains. Sperm counts in Western men have roughly halved in forty years. Young men today grip weaker than young men did in 1985. All three moving together is hard to dismiss.
A great-grandfather was the provider, protector, hunter, builder, judge and teacher. Each role was a contest, and his body had a reason to show up for it every day. Today the police protect, the supermarket replaced the hunt and HR judges. The roles hollowed out first. Then the body powered down equipment it had no contest for.
The Design Is Still There
A farm pig bred for nine thousand years to be docile grows a thick coat of bristles within months of being turned loose. Within a few generations its descendants look like wild boar again. The breeding switched the wild animal off, and the contest switched it back on.
The same design is still in every man. Millions of years of contests wrote the shoulders, the grip, the jaw and the voice, and that design responds when a contest returns.