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In the Light of Evolution Volume IV: The Human Condition
lution (Tattersall, 2000). Theodosius Dobzhansky (1975) wrote in 1962: “Following Weidenreich, Dobzhansky (1944) and Mayr (1950) entertained the hypothesis that only one human or pre-human species existed in any one territory at any one time level in evolutionary history.” But some years had passed and Dobzhansky now admitted a dead-end branch in the human genealogy, that of the paranthropines, or robust australopithecines: “In view of Robinson’s (1954) fairly convincing demonstration that two species of australopithecines may have lived in South Africa within a relatively short period of time, if not simultaneously, this hypothesis remains now probable only for the representatives of the genus Homo.” For Dobzhansky, anagenesis predominated over cladogenesis in human evolution: “Both cladogenetic and anagenetic changes took place in man’s ancestry but the latter predominated. Mankind was and is a single inclusive Mendelian population and is endowed with a single, corporate genotype, a single gene pool.” Whether or not the evolution of the genus Homo represents a single lineage (i.e., a single panmictic unit) that changes through time, passing through different evolutionary grades is a question that has been debated ever since, and it is the topic I deal with in the rest of this article.
Historically, most of the species of the genus Homo that have been proposed have been based on craniodental anatomy. The postcranial skeleton has barely played any role in the respective diagnoses, mainly because it is more poorly preserved in the fossil record. But we now have a sufficiently large sample to attempt a synthesis of evolutionary changes in the hominid (or hominin, as other authors prefer) body (Carretero et al., 2004) (Fig. 2.2). The results of this analysis, based on body plan, suggest very few species in the genus Homo. Why, then, should the cranium be privileged when classifying the hominids?
The first known hominid postcranial morphotype would then be that of A. ramidus, which could be the same (or not) as the other preaustralopithecines: Ardipithecus kadabba, Orrorin tugenensis, and Sahelanthropustchadensis.
The subsequent morphotype would be that of the australopithecines and paranthropines, as well as Homo habilis. To this, we also have to add the surprising Homo floresiensis from the late Late Pleistocene (Brown et al., 2004). This morphotoype is characterized by small stature, markedly wide relative width of the pelvis, and short legs. In fact, the poverty of the fossil record for the postcranial skeleton is such that the attribution of the australopithecine morphotype to H. habilis is based on only a single, very incomplete skeleton (OH 62 from Olduvai Gorge, dated to ~1.8 mya) that, craniodentally, preserves mainly the palate.
At a later point during the Early Pleistocene (now considered to begin at 2.6 mya), a morphotype appears within the genus Homo that is char-