Facts and Ideas in Paleolithic Growth Studies (Paleoauxology)

The Sima de los Huesos (Sierra de Atapuerca) cranial remains found up to and including the 1995 field season are described and compared with other fossils in order to assess their evolutionary relationships. The phenetic affinities of the Sima de los Huesos crania and a large sample of Homo fossils are investigated through principal component analyses. Metrical comparisons of the Sima de los Huesos and other European and African Middle Pleistocene fossils with Neandertals are performed using Z-scores relative to the Neandertal sample statistics. The most relevant cranial traits are metrically and morphologically analyzed and cladistically evaluated. The Sima de los Huesos crania exhibit a number of primitive traits lost in Upper Pleistocene Neandertals (especially in the braincase, but also in the facial skeleton), as well as other traits that are transitional to the Neandertal morphology (particularly in the occipital bone), and features close to what is found in Neandertals (as the supraorbital morphology and midfacial prognathism). Different combinations of primitive and derived traits (shared with Neandertals) are also displayed by the other European Middle Pleistocene fossils. In conclusion, the Sima de los Huesos sample is evolutionarily related to Neandertals as well as to the other European Middle Pleistocene fossils. In our opinion, all the European Middle Pleistocene fossils belong to the Neandertal lineage, and none can be included in an Afroeuropean common ancestor of Neandertals and modern humans.

The French site of Arcy-sur-Cure is a key locality in documenting the Middle-Upper Palaeolithic transition in Europe. Reliable attribution of the fragmentary hominid fossils associated with its early Upper Palaeolithic Châtelperronian industry has not been possible. Here we report the first conclusive identification of one of these fossils as Neanderthal on the basis of newly discovered derived features of the bony labyrinth. Dated at about thirty-four thousand years (34 kyr) ago, the fossil is representative of the youngest known Neanderthal populations, and its archaeological context indicates that these hominids used a rich bone industry as well as personal ornaments. The evidence supports the hypothesis of a long term coexistence with technocultural interactions between the first modern humans and the last Neanderthals in Europe. However, the complete absence of the derived Neanderthal traits in labyrinths of modern Upper Palaeolithic specimens from western Europe argues against phylogenetic continuity between the two populations in this region.

From birth to adulthood, the human brain expands by a factor of 3.3, compared with 2.5 in chimpanzees [DeSilva J and Lesnik J (2006) Chimpanzee neonatal brain size: Implications for brain growth in Homo erectus. J Hum Evol 51: 207-212]. How the required extra amount of human brain growth is achieved and what its implications are for human life history and cognitive development are still a matter of debate. Likewise, because comparative fossil evidence is scarce, when and how the modern human pattern of brain growth arose during evolution is largely unknown. Virtual reconstructions of a Neanderthal neonate from Mezmaiskaya Cave (Russia) and of two Neanderthal infant skeletons from Dederiyeh Cave (Syria) now provide new comparative insights: Neanderthal brain size at birth was similar to that in recent Homo sapiens and most likely subject to similar obstetric constraints. Neanderthal brain growth rates during early infancy were higher, however. This pattern of growth resulted in larger adult brain sizes but not in earlier completion of brain growth. Because large brains growing at high rates require large, late-maturing, mothers [Leigh SR and Blomquist GE (2007) in Campbell CJ et al. Primates in perspective; pp 396-407], it is likely that Neanderthal life history was similarly slow, or even slower-paced, than in recent H. sapiens.