In the chapter which Dr A. T. Hopwood wrote for my Olduvai book, published in 1951, he dealt with certain aspects of the fauna of Olduvai. He gave his interpretation of the fossil evidence then available in respect of the age of Beds I to IV. He concluded that these four beds formed ‘a single unit’ and that, in his own words, ‘there is no faunistic evidence to suggest that the lower part of the Olduvai series is of Lower Pleistocene age’.

In 1935 (Leakey, 1935) I had published the view that Bed I of Olduvai was of Lower Pleistocene age; but because of Dr Hopwood's categorical statement, based upon his study of the fauna, I later retracted this opinion, and in the 1951 book I accepted his suggestion and treated the whole of the main Olduvai sequence as belonging to the Middle Pleistocene. In spite of this, however, Dr D. G. Maclnnes and I felt constrained to point out that we considered the break between Beds I and II and Bed IV was more significant than Dr Hopwood had suggested. However, we accepted the fossils of Beds I and II as representing a single faunal unit, for we did not, in those days, see any reason to challenge the identifications which were given in Dr Hopwood's list.