Summer World_ A Season of Bounty - Bernd Heinrich [86]
One of the major selective pressures operating on the behavior, physiology, and appearance of vertebrate animals is sexual selection. Sexually selected traits vary enormously, yet they almost always signal something about the bearer that is correlated with survival value and the ability to produce or rear offspring. Survival and fertility markers, or features that can become correlated with strength and vigor—antlers, long tails, and so on—almost by definition become marks of “beauty.” The relevant features vary enormously from one species to the next, and what may be very attractive to one should and would probably be repugnant to another. For example, we don’t perceive the pale blue scrotum in the background of a bright red penis in the vervet and patas monkeys as a turn-on. The swollen red buttocks of a female chimp seem rather ugly to us, but to male chimps they are a sexual turn-on. If a solid, sleek coat of body hair in Neanderthals had, versus a thin, scraggly coat, survival value, then it would probably become a mark of beauty to them and it would have become more entrenched in their genome as a selected trait. It would be like the lack of body fur in warm-adapted Homo sapiens hunters. It would be like clothes to us, since clothes have become a necessity for our survival. As a matter of record, we do find body hair a turn-on, or else we would not fuss with it so much. I am talking of course, of head hair, which was probably of great survival value long ago at “crunch” times such as chasing down an antelope in the noonday heat. It may be selected for still, though not for the same reasons.
Fig. 35. Japanese macaques from the northern part of the island are densely furred, unlike any other living primates.
Large differences in sexual selection signals are especially important in closely related species, where interbreeding is a possibility. The songs and showy feather displays of birds are markers of fitness, but the males of the song sparrow sing entirely different notes and an entirely different repertoire from the white-throated; and the males of one finch species are bright yellow whereas other species are purple or indigo or green. We assume too much when we say that the Neanderthals valued the same things as we did and thus looked like us. External appearance relating to body fur or facial features, or clothes or lack of them, might have accounted for DNA evidence that now indicates there was no interbreeding between us and the Neanderthals. There is reason to believe there might have been outright aggression between the two species.
Neanderthals were probably low-tech survivors, or else more artifacts than crude campfires and scrapers would have been found. Would low technology then perhaps have been compensated for by some other attributes: fur and hibernation? If the Neanderthals hibernated in caves as the northern bears did (and if not, why not?), then we, the summer-adapted human hunters who invaded their territory, would probably have killed a Neanderthal as readily as we would kill a bear. But even if there was resemblance between us and the Neanderthals that could have inhibited our seeing them as prey, that would not have been an absolute deterrent. We are superbly adapted for making “us versus them” distinctions, on the basis of incredibly slight real differences and even on the basis of imagined or created stereotypes. This highlighting of differences is a psychological mechanism that divides, but the capacity to apply it to others probably evolved because it functions within the group to strengthen cohesion for “better” (more efficient) competition against other groups.