The years between the two world wars, which just preceded the emergence of the neo-Darwinian "new synthesis," were intellectually difficult ones for paleoanthropology in America. Patterns of thought deeply ingrained in biology and anthropology pushed writers on hominid evolution into interpretive "blind alleys." Most prominent among the patterns was what Ernst Mayr has called "typological thinking," which often mixed with a tendency to project "scientific" racism back into the hominid past. A "splitting" habit in taxonomy combined with these and with belief in "orthogenetic" change to make polyphyletism the norm.
Hesitance to accept as human ancestors any Pleistocene forms exhibiting "primitive" characters led to phylogenies which put the known fossils on side-branches. Anatomically modern humans were thus left "ancestorless" by most writers, though nearly all continued to use existing fossils in their evolutionary scenarios by designating them as "structural ancestors." Research conducted in Europe before 1914 on the Neanderthal skeleton and on the interperetation of endocranial casts, along with the Piltdown fraud, did much to establish these phylogenies and scenarios.
In tandem with these general themes came the ascendancy of several specific hypotheses that eventually clashed with accumulating evidence. That the brain had led the way in hominid evolution, that Neanderthals and other "low-brows" could be ruled out as ancestors, and that modern Homo sapiens had appeared early in the Pleistocene, became even harder to maintain. The close evolutionary bond between humans and great apes theorized in England by Sir Arthur Keith and elaborated in America by William King Gregory remained vigorous, however, despite challenge.
The present study examines these issues through an analysis of the five Americans whose writings on hominid evolution were most extensive and varied--Henry Fairfield Osborn, George Grant MacCurdy, Ales Hrdlicka, Earnest A. Hooton and William K. Gregory. The writings of each are analyzed separately, so that both general themes and responses to the changing state of the discipline can be traced. This approach reveals that shared patterns of thought did not prevent considerable diversity on nearly every main issue, a fact which rendered the field fertile for rapid growth later.
