One good thing can be said for Mortillet’s modified sequence of Abbevillian, Acheulean, Mousterian, Aurignacian, Solutrean, and Magdalenian. It may not be complete enough, and it may not apply too well to the world outside Europe; but it is chronologically sound locally. It is a succession of cultures along a time scale. If an archaeologist finds two or more varieties of paleolithic tools in a new site, he finds, for example, Acheulean beneath Mousterian, or Mousterian beneath Aurignacian. Similarly, when he comes upon Abbevillian and Acheulean in separate terraces of the same river, he always finds the Abbevillian in a higher terrace than the Acheulean, and, as we have explained on pages 51 and 52, the higher terrace is always the older.
Dating these cultures in terms of our years is another matter. The first step is fairly simple. If the tools are found with the fossils of a warmth-loving animal like the hippopotamus, they belong to an interglacial period; if they are found with the fossils of an animal like the hairy mammoth, which could survive a harsh climate, they belong to a glacial time. The species of animal may determine which glacial or which interglacial. If the tools are found in the gravel of a certain river terrace, then they belong to the geological period when the material of the terrace was being laid down. The terraces often contain fossils, and this may cross-date the terrace materials with cave deposits. But scientists are often faced with the problem of picking the right glacial or interglacial period on scanty evidence, and the still more difficult problem of setting the period in the terms of our years. There is room here for much disagreement. Glaciologists do not agree as to the age or the length of the various glacials and interglacials (see illustration, page 55). Some prehistorians accept and use the dates of one glacialist; some choose another’s. They do not all concur as to which culture came in which glacial period.
Men who practiced Abbevillian culture had some flaked tools—which they may have used for scraping—but their best-recognized output was a crude hand ax. It was not too well formed. Undoubtedly they also used wood and bone, but we have no sure evidence of this. Some assign Abbevillian culture to the first interglacial period, about 500,000 years ago. Some move it up 200,000 years, into the second interglacial. Some even place it in the third. Perhaps it lasted through all three. At any rate, the men who made it liked a fairly warm climate. As neither they nor their Acheulean successors made fire or controlled it effectively, the early Europeans probably retreated to Africa during the glaciations.