Shadows of Forgotten Ancestors

These behavior patterns also are encoded in the nucleic acids. Every deterrent flourish, every postural hint of submission, is meticulously written down in the ACGT language. That being the case, you might expect variations in the style or intensity of aggression from animal to animal within a given species, as is indeed the case. If you take a population of mice and breed the aggressive ones with each other and the peaceful ones with each other, eventually you produce two strains of markedly different temperament. This isn’t due to pup-rearing practices, because the young of aggressive parents, when raised by peaceful mothers, are aggressive, and vice versa. It’s a commonplace that through artificial selection dog breeders have produced nervous, high-strung, ferocious breeds—for example, rottweilers or pit bulls—and friendly, peaceful strains, often useless as watchdogs, such as cocker spaniels. In mouse and dog aggression, heredity often seems to take precedence over home environment. (It might be the other way around in humans, or the two influences might be evenly matched.)

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Nearly all the social mammals are organized as groups of females (often relatives) with their offspring. Males, otherwise absent, are conspicuously present when the females are in heat They may be busy dominating, fighting, or mating, but in terms of basic social structure and the bringing up of the young, they are often a shadowy presence. Usually, the young are raised by single mothers. Among the exceptions to this rule are chimpanzees, gorillas, gibbons, wild dogs, perhaps wolves. And, more than occasionally, humans.

In temperate and polar climates, there’s a good reason for the young to be born in the spring—so they may have the rest of spring and all of summer and autumn to grow up before having to face the rigors of winter. If the gestation period is short (or alternatively around a year), then mating will also occur in the spring. To arrange for biological clocks to be built into animals, to stimulate the reproductive machinery at the right moment in springtime and to inhibit it at other times of the year, must have occupied great vistas of evolutionary time.

Natural selection has provided a wide range of visual, olfactory, auditory, and other cues to inform the normally uninterested males of the otherwise indetectable fact that ovaries are releasing eggs all around them. Sexual attention at other times is generally a wasted effort (it’s used to bond male and female in species where both are needed to raise the young). So the female is designed with some internal calendar (perhaps triggered by the length of the day), and a series of signals and behaviors (alluring pheromones plus enticing postures, say). In the season of love, on cue, as if activated by some Cartesian clockwork, both sexes become mad with passion.

If mating is to occur in the spring, then the rivalry of males for the attentions of females should also peak in the spring. If the lives of deer depend in part on their speed and their ability to fight back when cornered by predators, then intraspecific tests of strength, speed, stamina, and strategy among stags are to the benefit of the genes of the victors as well as to the deer clan. This is ritualized combat, almost never to the death. The point of the exercise becomes instantly clear as the doe gives herself to the winner. A multitude of such dramas over many generations helps deer keep pace with hereditary improvements in, for example, the hunting skills of wolves.

In many predatory species, animals hunt together. Prey is flushed into ambush, or is exhausted by repeated feinting. Stragglers, usually the weak, the young, and the old, can be isolated. The predators may adopt a relay system, Group One performing feints only, and Group Two loping along to pick up the attack when Group One is exhausted. Cooperation makes hunting much more efficient, and the predators may now bring down animals much larger than they are.

Members of hunting packs have a kind of ethic: Whatever rivalries they bear are put aside during the hunt. For them too, “politics stops at the water’s edge.” There’s a different set of social rules within the group than without. But it’s an easy step from attacking animals of other species to attacking strangers of the same species. This is true of dogs and lions, which hunt in packs, and of ants and penguins, which do not. They behave as if special loyalty is owed to their group only; suspicion and hostility are due all others, even though they are fellow members of the same species. And this is not restricted to hunting packs. It’s a fact of life among most sociable birds and mammals.