Fri, Feb 22, 2013 - Page 9 News List

Neanderthal DNA forms part of the modern human stew

What defines a modern human? The biological answer is simple: A member of the species Homo sapiens that is characterized by such features as a relatively large brain set in a globular braincase, small brow ridges over the eyes, a small retracted face, a chin on the lower jaw, and a lightly built skeleton. Many of modern humans’ biological traits — at least those that can be preserved as fossils — were already present in Africa and Israel more than 100,000 years ago.

However, other factors — such as complex societies, ceremonies, spiritual beliefs, art, music, technology and language — also characterize modern human populations. Which traits are crucial to the definition of a “modern human” and how far back can the classification be applied?

Given that humans’ morphological and behavioral characteristics evolved at different rates, this question is a source of controversy. Indeed, paleontologists studying the physical origins of Homo sapiens will inevitably differ from archeologists reconstructing ancient behavior over what constitutes an early modern human.

Recent discoveries in paleontology, archeology and, especially, genetics of striking similarities between extant humans and some ancient populations, are further complicating assessments of modern humans’ origins. One leading idea was that modern humans’ primitive ancestor Homo erectus left Africa nearly 2 million years ago and dispersed into other areas of the world. Regional populations then steadily evolved into Homo sapiens, with modern human behaviors first emerging in Europe roughly 40,000 years ago.

However, new evidence suggests that modern humans evolved relatively recently in Africa — and that the transformation that they underwent after their departure about 60,000 years ago was far from seamless. Specifically, studies of Homo sapiens’ close but extinct relatives, the Neanderthals, are revealing new facets of modern human development, while intensifying the long-running debate over the differences between the two species’ behavioral capabilities.

Growing archeological evidence of key elements associated with Homo sapiens is emerging at sites in Africa that are more than 60,000 years old. These include complex tools (which require several stages of manufacture), symbolism (for example, red hematite pigments for notation and beads for display, made from sea shells and ostrich eggshells) and long-distance networks of contact and exchange. These discoveries support some archeologists’ view that only Homo sapiens was advanced enough to be considered truly modern humans, while non-modern groups like the Neanderthals displayed, at best, only incipient signs of such complexity.

Moreover, genetic evidence, based on distinct DNA coding that is known to be related to brain functions in modern humans, suggests at least some cognitive contrasts between Neanderthals and Homo sapiens. And demographic differences (small, low-density populations) may have hindered Neanderthals’ cultural evolution, compared with the wider networks established by early modern human groups, initially in Africa and subsequently worldwide.

However, evidence also suggests that some Neanderthals buried their dead with grave goods (items presumably intended to help the deceased in the afterlife), produced complex tools (such as stone armatures mounted with mastics) and developed personal symbols (including manganese oxide pigments and pendants made from animal teeth). They apparently also used plants with medicinal properties.

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