The Descent of Man, human nature and the nature/culture divide

How does human nature, especially as typically construed within an imposed nature/culture divide, fit into Darwin's keen and detailed descriptions of animate life? My answer will point out omissions on each side of the nature/culture divide, a divide academically evident in the division between 'the humanities' on the one side and 'the sciences' on the other. It will proceed to concentrate attention pre-eminently on an incredible lacuna in today's scientific research, and in research generally over the 138 years since The Descent of Man and Selection in Relation to Sex was published, namely, on the lack of recognition of, and in turn the lack of penetrating and self-enlightening research on, 'the law of battle' as a real human phenomenon. As described by Darwin, 'the law of battle' is a biological matrix, natural to humans as to other animals, though tempered by 'civilization'. As I will show, variously aided and abetted, the matrix has not only been reduced to a cellular phenomenon, i.e. sperm competition, but has been culturally elaborated - culturally 'exapted', to borrow Gould and Vrba's term - to subserve strictly cultural ends far beyond the original, ends having to do with the pursuit of various forms of 'cultural fitness', and this from the beginnngs of recorded human history.