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Focusing on the question of trends in Homo erectus cranial capacity evolution, Rightmire contends to have reanalyzed the data and demonstrated “a pattern of change … quite different from that described by Wolpoff.” Accepting the procedures used in this earlier analysis (Wolpoff 1984), he does this by changing the composition of the Homo erectus sample.
With a sample of 94 Pleistocene cranial capacities between the time period of 1.8 Ma and 50 Ka now known, we consider the evolution of cranial capacity in Homo, with the null hypothesis that the changes over time are a result of one process. We employ a new method that uses a resampling approach to address the limitations imposed on the methods of previous studies. To test the null hypothesis, we examine the distribution of changes in adjacent temporal samples and ask whether there are differences between earlier and later samples. Our analyses do not reject the hypothesis of a single process of brain size change, but they are incompatible with an interpretation of punctuated equilibrium during this period. The results of this paper are difficult to reconcile with the case for cladogenesis in the Homo lineage during the Pleistocene.
Using a conservative definition of the hominid taxon Homo erectus, the sample of specimens known at this time, 92 individuals in all, is examined to determine whether the species exhibited significant temporal trends or evolutionary stasis. The sample is divided into three low-resolution time spans, and it is shown that significant change characterizes a number of cranial, mandibular, and dental features. Rates of change are comparable to or above rates reported for other fossil vertebrate lineages sampled over a similar duration. The often repeated assertion that Homo erectus is an example of a species in evolutionary stasis is incorrect.
It is broadly agreed that all recent/living human populations ultimately descend from Africans. In this chapter we examine new anatomical and genetic evidence that addresses one way this could be the case, a unique recent African origin for living humanity (meaning that all living humans descend from recent Africans and only descend from recent Africans, by species replacement). The male cranium from Herto (BOU-VP-16/1) is useful for examining this issue. Its description (White et al., 2003) raised questions about both the origin of recent humans and the fate of the Neandertals. Together, these two questions address the pattern of recent population evolution because if the ancestry of recent populations is uniquely African, Neandertals can have played no significant role in their evolution. The hypothesis we examine here is whether Neandertals were the end point of a species-lineage that was distinct from a different African species-lineage, including Herto, leading to recent humans. We examine the possibility of unique African origins by assuming this hypothesis is correct, and testing for the presence of evidence addressing its consequences. Specimens on a distinct Neandertal species-lineage are expected to be more different from Herto than they are from the common ancestors of Herto and Neandertals because there is more genetic distance from Herto to the Neandertals than there is from either Herto or the Neandertals to their common ancestor. We quantify the similarity of the large Herto male to 12 other mostly or fully complete Middle and Late Pleistocene male crania from Africa and other regions of the world, to test for this pattern of similarity. We also examine whether similarities between Herto and other Pleistocene Africans reveal a distinct African palaeo-deme.1 We show that comparisons of other crania to Herto indicate that the penecontemporary Europeans are not evolving in a different direction than the Africans. This result is supported by direct evidence of interbreeding between members of this Herto-descendent palaeo-deme and Neandertals, found in the analysis of Neandertal nuclear DNA. There is demonstrable, significant influence of the Neandertal genome on human genetic variation today (Green et al., 2010; Yotova et al., 2011). The Neandertal influence involves genes that evolved in Neandertals and other archaic populations and spread through non-African populations under selection. These data refute the hypothesis of a Neandertal species-lineage and support the interpretation of an African palaeo-deme in the Pleistocene that is one of the ancestors of living humans; hence, the African origin of recent humanity is one of several sources. The African palaeo-deme is not a species-lineage, and Neandertals are also among the ancestors of living Europeans and other non-African populations. Their influence is such that our ancestors would not have become modern without them.
The claim may be advanced that in the Afro-Asian land-mass, the true placement of the Garden of Eden, in the sense of the cradle of recent humanity, was in Africa, but it is far more likely to have been in ancient, 1 mya Africa, than in recent, 200,000 year-old Africa.