Molecular biology has recently provided genetic evidence indicating that some interbreeding between Homo sapiens and Homo neanderthalensis likely occurred. Erect posture and large brain are the two most conspicuous human anatomical traits. The advent of culture has brought with it cultural evolution, a superorganic mode of evolution superimposed on the organic mode, which has, in the last few millennia, become the dominant mode of human evolution. Ethics and ethical behavior may serve as a model case of how we may seek the evolutionary explanation of a distinctively human trait. Humans evaluate their behavior as either right or wrong, moral or immoral, as a consequence of their eminent intellectual capacities, which include self-awareness and abstract thinking. Ethical behavior is an attribute of the biological make-up of humans and is, in that sense, a product of biological evolution. One major contribution of sociobiology to evolutionary theory is the notion of inclusive fitness.

The main point of the architect analogy was to emphasize the importance of natural selection relative to the production of variation. Some of Darwin's otherwise staunchest supporters felt he had, in the Origin, given short shrift to variation as a factor in evolutionary change. This chapter concerned with the development of the architect analogy, and with the alternative conceptions of evolution suggested by the different versions. Michael Ruse has long insisted that Darwinian evolutionary theory is a design theory through and through. Following the publication of the Origin, Charles Darwin took the opportunity to clear up some issues left unclear in the book, including his position on the importance of selection relative to the production of variation. Darwin himself had focused on the ways in which particular outcomes of evolution can be due to particular, happenstance courses of variation in his book on orchid evolution, published immediately after the Origin.