He attributed the "great break in the organic chain between man and his nearest allies" to extinction, and as spreading civilisation wiped out wildlife and native human cultures, the gap would widen to somewhere "between man in a more civilised state, as we may hope, than the Caucasian, and some ape as low as a baboon, instead of as at present between the negro or Australian and the gorilla." While there "can be no doubt that the difference between the mind of the lowest man and that of the highest animal is immense", the "difference in mind between man and the higher animals, great as it is, is certainly one of degree and not of kind." At the same time, all human races had many mental similarities, and early artefacts showing shared culture were evidence of evolution through common descent from an ancestral species which was likely to have been fully human.