A uniquely modern human pattern of endocranial development. Insights from a new cranial reconstruction of the Neandertal newborn from Mezmaiskaya.

The globular braincase of modern humans is distinct from all fossil human species, including our closest extinct relatives, the Neandertals. Such adult shape differences must ultimately be rooted in different developmental patterns, but it is unclear at which point during ontogeny these group characteristics emerge. Here we compared internal shape changes of the braincase from birth to adulthood in Neandertals (N = 10), modern humans (N = 62), and chimpanzees (N = 62). Incomplete fossil specimens, including the two Neandertal newborns from Le Moustier 2 and Mezmaiskaya, were reconstructed using reference-based estimation methods. We used 3D geometric morphometrics to statistically compare shapes of virtual endocasts extracted from computed-tomographic scans. Throughout the analysis, we kept track of possible uncertainties due to the missing data values and small fossil sample sizes. We find that some aspects of endocranial development are shared by the three species. However, in the first year of life, modern humans depart from this presumably ancestral pattern of development. Newborn Neandertals and newborn modern humans have elongated braincases, and similar endocranial volumes. During a 'globularization-phase' modern human endocasts change to the globular shape that is characteristic for Homo sapiens. This phase of early development is unique to modern humans, and absent from chimpanzees and Neandertals. Our results support the notion that Neandertals and modern humans reach comparable adult brain sizes via different developmental pathways. The differences between these two human groups are most prominent directly after birth, a critical phase for cognitive development.

Neanderthal brain size at birth provides insights into the evolution of human life history.

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.

ESR at Treugol'naya Cave, Northern Caucasus Mt., Russia: dating Russia's oldest archaeological site and paleoclimatic change in Oxygen Isotope Stage 11.

At 1510 m asl, Treugol'naya Cave, Russia, is the highest cave showing evidence for human occupation in eastern Europe. Layers 4-7 in the 4.5-m-thick sequence yielded many artifacts representing Lower Paleolithic pebble and flake tool industries. Abundant faunal remains include extinct Middle Pleistocene species. Palynological, paleomagnetic, and microsedimentological analyses indicate that several climatic changes of different magnitudes occurred in the sequence. To determine absolute ages for Treugol'naya, 32 independent subsamples from nine ungulate teeth collected from the Lower Paleolithic layers were dated by standard and isochron electron spin resonance (ESR) analyses. Isochron analyses indicate that the teeth experienced no significant U leaching or secondary uptake, and that linear uptake (LU) provides accurate ages. Layers 4b through 5b dated to 365+/-12-406+/-15 ka. Therefore, hominids visited the site periodically throughout Oxygen Isotope Stage (OIS) 11, indicating that they utilized resources at elevations >1000 m at least seasonally by 400 ka. ESR, paleomagnetic, palynological and paleontological analyses all indicate that the Lower Paleolithic Layers 4-5 correlate with OIS 11. The thickness of Layers 4-5 (more than 1.5 m) makes this one of the thickest OIS 11 terrestrial deposits known.