Two distinct camps are waging the current debate over the actual age of anatomically modern humans. Each of these has a preference for different types of evidence. In early 1996, Allan Wilson's laboratory at Berkley announced the discovery of what they termed 'Mitochondrial Eve', the single ancestral mother of all humans alive today. The types of evidence the Berkley team employed were a combination of statistics and genetics. Wilson and his team examined patterns of genetic variation of the mitochondrial DNA among modern humans and analysed the variations to show that all humans share a common maternal ancestor who lived in Africa around 100,000 to 140,000 years ago.
However, since Wilson first published his results, a number of possible problems have been noted. These include possible miscalculation of the speed of genetic change, and hidden events such as occasional crashes in local population densities, which would skew the results. A number of those who are worried by Wilson's work reject the use of mitochondrial DNA to establish a date altogether. They are unhappy with the type of evidence being used. Instead, they insist that, as David Frayer of the University of Kansas put it; "Fossils are the real evidence".
Some argue that the evidence from fossils seems to suggest that modern humans are not a new species which emerged from Africa, but are the direct descendants of earlier hominids who have lived for far longer across the globe. Milford Wolpoff of the University of Michigan has studied the anatomy of hominid fossil skulls and concluded that in Europe at least, modern humans are descended from Neanderthals. To be specific, he does not believe that Neanderthals are a separate species at all. Colin Tudge states that, "At most, he (Wolpoff) sees them only as a sub-set or sub-species of ourselves." Wolpoff's favoured type of evidence is the direct comparison of size and shape of various features that are shared between skulls from right across the Palaeolithic eras. Wolpoff's position is known as the 'multi-regional hypothesis. However, this is a minority view since the publication of the effect of mitochondrial DNA on human populations.
One or other of these results must be wrong, so other techniques may help us resolve the issue. Thermoluminescence dating now provides absolute dates for finds within the ranges mentioned. This technique analyses the release of light from a crystal lattice (typically from the mineral crystals in pottery sherds), which shows the amount of alpha radiation the lattice has taken up since it was last heated to a high temperature. This method has allowed the re-dating of burnt flint found with early modern skeletons in Jebel Qafzeh cave in modern Israel, previously dated around 40,000 years ago. Thermoluminescence reveals these assemblages to be actually 90,000 years ago. The original dates had been an important part of Wolpoff's arguement so n this case the new evidence would seem to add weight to Wilson's mitochondrial Eve hypothesis.
Closely related to the debate about the timings of the emergence of modern humans is the debate surrounding the location for this event. As we have seen, Wilson's genetic analysis leads him to conclude that modern humans arose in Africa and spread out thereafter. The 90,000 BP date for the Qafzeh skeletons does not contradict this. However, Wolpoff, who as we have noted, disputes the African Eve hypothesis, believes that modern humans evolved concurrently all over the globe. He bases his multiregional hypothesis of human evolution on anatomical analysis of skulls. Wolpoff examined differences between many skulls found at archaeological sites across the globe and showed that a consistent typography runs through Europeans and includes Neanderthals. This he argues means that modern Europeans must be directly related to Neanderthals and thus cannot have emerged in Africa alone.
Recently some new studies which concentrate on of DNA from cell nuclei indicate that certain DNA sequences present in people today originated in archaic humans who lived in Eurasia before the first modern humans appeared. This then may support mutiregionalism rather than Out of Africa theories. Until geneticists sort out their data it will be impossible to deduce which DNA sequences we need to investigate. Until such time it will be difficult to know what contribution Neanderthals and other may have made to our genetic makeup.
Renfrew,C. and Bahn,P. Archaeology: Theories, Methods and Practice.
Tudge, Colin The Day before Yesterday
Chris Brown ©2002
Copyright 2002-2003 newarchaeology.com
Website hosted by 1&1.co.uk