 He referred to seven evolutionary assumptions which he felt lacked sufficient evidentiary support.Kerkut concludes his 1960 book with the statement "It is not clear whether the changes that bring about speciation are of the same nature as those that brought about the development of new phyla.The answer will be found by future experimental work and not by dogmatic assertions that the General Theory of Evolution must be correct because there is nothing else that will satisfactorily take its place.