Shadows of Forgotten Ancestors

Among reptiles, amphibians, and even crustaceans, dominance behavior is common.¹⁵ The varanids (such as the komodo dragon) are very good at ritualized and stereotyped intimidation displays. They rattle or lash their tails, rear up on their hind legs, inflate their throats, and, if their rival has not yet submitted, attempt to wrestle him to the ground. In crocodiles, dominance is established by slapping the head into the water, roaring, lunging, chasing, and biting, pretend or real. When interrupted in his mating embrace, a male frog croaks; the deeper his croak, the greater his implied size when disengaged, and the more diffident is the would-be intruder. A toothless, brightly colored Central American frog, genus Dendrobates

, intimidates intruders by performing a vigorous sequence of push-ups. But among the skinks, in which aggression is released seasonally when the heads of the males turn bright red, the virtues of intimidation by bluff are often lost sight of, and the two rivals tear into each other without so much as a preliminary throat swelling. When hermit crabs introduce themselves, they devote a few seconds to taking each other’s measure—by stroking one another with their antennae; the smaller then promptly submits to the larger.¹⁶ Stalk-eyed flies do the same; the more dominant individuals are the ones with the more widely separated eyes.

It’s rare that any male starts out as an alpha. Generally you have to work your way up through the ranks. But in the intervals between your challenges it would be a mistake to be too disruptive. Even for the very ambitious a talent for subordination and submission is needed. Also, it’s hard to predict who will achieve high-ranking status. Sometimes greatness is thrust upon unsuspecting animals by the course of events. Accordingly, everyone needs to be able to rise to the occasion. If you’re in a linear hierarchy, you must know how to dominate the animals below you and submit to those above. An inclination for both dominance and submission must beat within the same breast. Complex challenges make for complex animals.

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Nothing we’ve said so far indicates anything about female preference. What if she finds the alpha male arrogant, boorish, taking too much for granted? Or just plain ugly? Does she have the right to refuse? At least among hamsters, this is not an option.

Here’s an experiment¹⁷

done on Syrian hamsters by the psychologist Patricia Brown and her colleagues: To begin, males, matched for size and body weight, were allowed to interact with one another in pairs to establish dominance. Chasing and biting were among the behaviors counted as dominant; defensive postures, evasions, raised tails, and full cowering submission were counted as subordinate traits. The dominants accounted for over ten times more aggressive acts than an equal number of subordinate animals; the subordinate animals tallied ten times more submissive acts than those judged dominant. It never took more than an hour for a pair of hamsters to decide who was dominant and who was subordinate.

Now although these males knew how to fight, they’d never had a sexual experience. Each of them was made to wear a little leather harness attached to a tether, which, like a dog’s leash, limited how far he could roam. Next, an ovulating female was released; she could have access to the tethered males, but beyond a certain point their leashes would prevent them from following her or offering unwelcome attentions. Whatever sexual contact might be in the offing would be on her terms.

We imagine her, steely-eyed, slowly looking the males over head to tail in their kinky leather outfits. Because the earlier dominance conflict was largely ritual, there were no injuries to betray which was the subordinate animal. Each male was in its own partitioned area, so they could not see one another and betray to the female their relative status through gestures of dominance or submission. Would she, despite the absence of signs apparent to the human observers, select the dominant male? Or would she find some other trait more attractive? The females were not hesitant or demure. In less than five minutes, every one of them presented herself for copulation to one of the males. In every case it was the dominant male. Prior familiarity was not required. Somehow she knew. There were no questions asked about his education, family, financial prospects, or the gentleness of his disposition. Every female was eager for sex with the dominant male.

How could the female know? The answer seems to be that she could smell dominance. There is literally a chemistry between them, the odor of power. The dominant males give off some effluvium, some pheromone that subordinate males do not.¹⁸