Competing for the Best Mates
Then there is sex. In most mammalian and bird species, there is competition between males for access to females. Such competition can take many forms, but often it entails driving off or outperforming would-be suitors in hopes of impregnating a suitable female. In mating season, in full rut, a couple of bull moose, for example, will fight head-to-head until one finally tires or recognizes his weaker position and scuttles off. In a baboon troop, the alpha male has greater privileges with the troop females than do other males, and he will fight challengers to maintain his status. The lower-ranking males find ways of mating out of sight of the alpha male, sometimes involving significant deception.
Using a different strategy, male bowerbirds build fancy structures to attract females, and competing males will, on the sly, try to wreck them. And among blue Manakins, the males dance, each trying to outperform the other. Females select those perceived by them to have the most sophisticated dance—or so it seems to a human observer. The females select the male, and for these bird species, aggression is less important than performance, presumably because performance has come to signify what the female wants in a mate—virility and competence (a good brain).
Human mating behavior is more complicated. Like much human of behavior, it is subject to such a high degree of shaping by cultural norms and conventions, by fads and trends, that you can only marvel at the flexibility of the human brain. Sometimes human mating behavior seems to have borrowed something from the bowerbird, something from the head-butting moose, and something from the lekking of the sage grouse. In humans, as in most other mammalian species, males compete for females. There are displays, often conventionalized within the norms of a culture: displays of power, strength, wealth, beauty, generosity, cleverness, and social status. Depending on the culture, females may also compete with each other, and female selection may play a major role in mating.
Aggression is multidimensional. It has multiple triggers, variable mixes of emotions, and variable manifestations. It can serve any one of a set of diverse purposes. Within a species, there is apt to be considerable variability among individuals in the taste for aggressive behavior. Being slow to anger may serve animals better in times of peace and plenty, whereas a hot-tempered disposition may be more beneficial during times of scarcity or war. Moreover, an animal may be quick to respond in defense of the brood, but slower in preparation for an attack on prey.
Male and Female Brains
In our school, fighting was not allowed in the school yard, so the boys who wanted to fight marched over to the footbridge that crossed the irrigation flume, just over the edge of the school’s boundary. This was a good venue, as onlookers could seat themselves along the bridge rails and cheer on their favorite. These fights did not amount to much other than the odd bloody nose and a generous helping of crow. The teachers let it go unless the frequency was considered too high, whereupon the principal called in the likely suspects and gave them the strap. That kept the business in bounds. The girls did not fight. They gossiped. They could, of course, be spiteful and cruel, especially to other girls, but they did not actually engage in a slugfest. This tends to be the pattern worldwide, though of course local customs and biological variability allow for exceptions.
It is well known that human males more commonly engage in physical fights than females. The rates of convictions for assault, battery, and murder are vastly higher in men than in women. Men are typically the ones who hold up the stagecoach, rob the banks, go to war, and knife their way out of a bar fight. This is true pretty much everywhere. What explains this difference between males and females?