This we observe in ourselves today. It depends upon whether or not he understood the consequences. The fossil record and comparative anatomy of living primates are interpreted to support the view that larger brains go with the more intelligent primates. Until we know a great deal more than we do about the detailed function of brain structure in all the primates, we can only guess and appeal for our answer to the archaeological record of toolmaking.
Cranial volume is a trait much overemphasized by anthropologists and others.
Furthermore, the brain consists of many structures, only some of which are concerned with such high-level activities as speech, intellect, toolmaking, and anthropology. The smaller end of the range is not correlated with mental insufficiency. I suspect, therefore, that only with the evolution of Homo habilis did some form of spoken language begin. The change in the shape of the basicranium is to be seen in the earliest-known Homo erectus specimen, skull 3733 from northern Kenya, dating from almost 2 million years ago. According to this analysis, this Homo erectus individual would have had the ability to produce certain vowels, such as in boot, father, and feet.