Let's assume, as many do, that the mind––the mental, the affective 'self'––is wholly a function of the somatic operations. This means, in part, that mental 'drives' or urges are no more or less semiosically relevant than other somatic components. For example, as evolutionary psychologists would have it, our incessant psychic urge to have sex is but a function of the evolutionary encoding in our bodies, based on the reproductive success of such urges over numerous prior generations. Likewise, as biologists recognize, the design of the human hand is but a function of similar prior selection pressure on our somatic makeup. We know the function of our hands by recognizing how we can use them now as well as understanding how their evolution brought our species this far. Our entire 'psychosomatic' makeup is a sign of our species' natural ends, as they are progressively sculpted and optimized by natural selection.
The problem is that the same evolutionary thinking is typically used to cut back against finality per se, by saying there is no 'intrinsic' functional (semiosic) link between our somatic makeup and our ethical choices. To wit, just because a man has a penis and semen and a woman has a vagina and ova, does not mean this is an intrinsic 'sign' of some 'higher' natural order.
Yet, note the perilous tension in this argumentation. The ethical defense of, say, homosexual behavior is that it's "natural" for homosexuals to feel and act as they do. It is, in other words, what everything in their psychic makeup points to, the contradictory indications of their gentilia be damned. Yet we had already agreed that even the psyche is but a dimension of somatic semiosis. So we face a dilemma. If homosexual urges are intrinsically signs of a homosexual's natural dispositions, which must be defended precisely because they are his proper nature, then we concede that there are genuinely proper ends of human nature. On the other hand, if we deny that homosexual urges are intrinsic signs of human nature, then we force a cleft between the psyche and the body's construction, a cleft which secularism cannot abide. If they are metaphysically unified, identical, no less, then by what criteria do we trump the semiosis of the body with the semiosis of the psyche? Is this trumping not an argument for the radical freedom of the 'self' from any and all antecedent causal constraints which simply happen to be encoded in the body?