单项选择题

Passage Five

Some modern anthropologists hold that biological evolution has shaped not only human morphology but also human behavior. The role those anthropologists ascribe to evolution is not of dictating the details of human behavior but one of imposing constraints-ways of feeling, thinking, and acting that "come naturally" in archetypal situations in any culture. Our "frailties" --emotions and motives such as rage, fear, greed, gluttony, joy, lust, love--may be a very mixed assortment, but they share at least one immediate quality: we are, as we say, "in the grip" of them. And thus they give us our sense of constraints. Unhappily, some of those frailties--our need for ever-increasing security among them--are presently maladaptive. Yet beneath the overlay of cultural detail, they, too, are said to be biological in direction, and therefore as natural to us as are out appendixes. We would need to comprehend thoroughly their adaptive origins in order to understand how badly they guide us now. And we might then begin to resist their pressure.

It can be inferred that in his discussion of maladaptive frailties the author assumes that ______.