Evolutionary theory, systematics, and the study of human origins.

Abstract

Paleoanthropology's relationship with evolutionary theory has not been entirely happy. The anatomists who dominated paleoanthropology for its first century had little interest in biological diversity and its causes, or in hominins' place in that diversity, or in the rules and principles of zoological nomenclature - which they basically ignored entirely. When, as the twentieth century passed its midpoint, Ernst Mayr introduced theory to paleoanthropology in the form of the gradualist Modern Evolutionary Synthesis (in its most hardened form), he shocked students of human evolution not only into a strictly linear evolutionary mindset, but into a taxonomic minimalism that would for years obscure the signal of phylogenetic diversity and vigorous evolutionary experimentation among hominins that was starting to emerge from a rapidly enlarging hominin fossil record. Subsequently, the notion of episodic as opposed to gradualist evolution re-established phylogenies as typically branching, and species as bounded entities with births, histories, and deaths; but the implications of this revised perspective were widely neglected by paleoanthropologists, who continued to reflexively cram diverse new morphologies into existing taxonomic pigeonholes. For Pleistocene hominins, the effective systematic algorithm became, "if it isn't Australopithecus, it must be Homo" (or vice versa), thereby turning both taxa into wastebaskets. The recent development of the "Extended Evolutionary Synthesis" has only exacerbated the resulting caricature of phylogenetic structure within Homininae, by offering developmental/phenotypic plasticity as an excuse for associating wildly differing morphologies within the same taxon. Homo erectus has been a favorite victim of this foible. Biological species are indeed morphologically variable. But they are only variable within limits; and until we stop brushing diverse morphologies under the rug of developmental plasticity, paleoanthropology will remain at a major impasse.