At The Scientist, Ian Tattersall describes the early days of anthropological studies:
Before the mid-1900s, human fossils were for the most part studied and pronounced upon by specialists in human anatomy. Based in medical schools, these researchers were exquisitely attuned to variation within Homo sapiens, but were largely unconcerned with the riotous diversity of species out there in the living world. Ignorant of taxonomic norms, they branded newly discovered hominin fossils with new Latin names, much as they gave each of their children a separate name. In this way, throughout the first half of the 20th century the rapidly expanding paleoanthropological literature became littered with formal names — even though many of the freshly unearthed fossils actually belonged to species that had already been described.
I write about this crucible of discovery and folly in my new book, The Strange Case of the Rickety Cossack.
The haphazard application of species names to every new hominin fossil was a practice that could not continue indefinitely. And in 1950 the ornithologist Ernst Mayr, one of the fathers of the Evolutionary Synthesis, took it upon himself to lecture the paleoanthropologists on the error of their ways. The Synthesis was an elaboration of evolutionary theory that saw most evolutionary change as the gradual accumulation, via natural selection, of small genetic innovations within ancestor-descendant sequences. So Mayr depicted human evolution as the slow modification of a single lineage culminating in Homo sapiens. Among the fifteen hominin genera then described, Mayr said, there was in reality only one: our own genus, Homo. What’s more, the Homo lineage contained only three species: Homo transvaalensis (an early biped) had given rise to Homo erectus, which in turn had evolved into Homo sapiens. Acutely aware that their nomenclatural proliferation lacked any theoretical justification, the paleoanthropologists capitulated. For half a century thereafter, most of them viewed human evolution as a single-minded progression from primitiveness to sapient perfection driven by natural selection: an idea that fit rather well with the undeniable fact that only one hominin exists in the world today.
From the beginning, though, it was obvious that Mayr’s scheme was a huge oversimplification. As fossil discoveries rapidly continued to accumulate, his single lineage began to bulge at the seams. A new image of hominin evolution began to develop.