Much of the difficulty that people have had in the past with evolutionary approaches to human psychology and behaviour arose from the tendency of twentieth-century evolutionists to ignore the mind and concentrate wholly on genes and/or behaviour. According to George Williams, one of the most important of twentieth-century Darwinists:only confusion can arise from the use of an animal-mind concept in any explanatory role in biological studies of behaviour. ... Mind may be self evident to most people, but I see only a remote possibility of its being made logically or empirically evident. ... I feel intuitively that my daughter's horse has a mind. I am even more convinced that my daughter has. Neither conclusion is supported by reason or evidence. Only if it violates physical laws would mind be a factor that biologists would have to deal with. ... There is no such evidence for mind as an entity that interferes with physical processes, and therefore there can be no physical or biological science of mind. ... no kind of material reductionism can approach any mental phenomenon.
