BaccalaurÉat gÉnÉral et technologique

Session 2012

ÉPREUVE SPÉCIFIQUE MENTION « SECTION EUROPEENNE OU DE LANGUE ORIENTALE »

Académies de Paris-Créteil-Versailles

Binôme : Anglais /SVT

Sujet n° 4

THEME : Human Evolution

Humans' Chimeric Origins.

If you thought we were the direct descendents of an ape from east Africa, hold it right there. The origin of our species is being called into question in ways that challenge the roots of our identity.

First, we may not have come from east Africa. Two remarkably complete, 1.97-million-year-old hominin fossils discovered in South Africa suggest modern humans could have evolved outside the Rift Valley. This suggests that human-like apes may have been evolving in parallel in different places around Africa. The more we find out about these animals the more we will learn about the key transitions along the path to modernity: when hominins lost their body hair and when they first started using tools.

Second, there's no such thing as a standard-issue human. All non-Africans owe 2.5 per cent of their DNA to Neanderthals, the result of matings between Homo sapiens and Neanderthals 60,000 years ago. And Melanesians owe an additional 5 per cent to another hominin, the Denisovans. Some of us may carry the genetic left-overs of cross-breeding with other extinct people as well.

As more fossils are found and their DNA is sequenced, we should get direct evidence of the biology of these extinct cousins and what makes us different from them. What we have in common is just as interesting. We are a muddled up, chimeric species. While many people long for something to define us as uniquely human we may find that there is no such thing.

by Catherine Brahic, New Scientist, 21 December 2011

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