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Tracing mother Eve using mitochondrial DNA

Mother Eve in dispute with ape-man

Present day archaeology continues to be in conflict with the relative newcomers, the biochemists, who claim to be able to date the origins of present-day humans from various molecules to be found in the cell, one of which, mitochondrial DNA (mtDNA) is the subject of this article.

Archaeologists currently date the earliest assumed finds of modern man, Java Man and the Chinese fossils at 1,000,000 and 750,000 years before present respectively. In contrast, the biochemists quote values of 140,000 to 290,000 years before present to trace all mankind back to a single female, dubbed `Mother Eve'. This `tracing back' of the family tree has been done by studying living individuals from several populations and examining the differences between their mtDNA. These differences will have built up over the past generations by miscopyings, mutations, during reproduction. Further to this, recent work with mice, which is thought to be applicable to humans, suggests that these dates could be roughly halved because of evidence that mtDNA can be contributed by the father in about one case in every 1,000.

These relatively recent dates are proposed by biochemists because of the great similarity of the mitochondrial DNA in all human beings. The estimate presents difficulties for both those archaeologists who consider the origin of modern humans from their forerunners to have occurred in many places at roughly the same time (multiregional origins) and those who maintain that modern man originated at one time in one place and subsequently spread by migration (single origin).

From the multiregional model of origins it would be anticipated that there should be more variation in the types of mtDNA than if there was one original population because of the different genetic composition of the ancestral hominids.

For the archaeologists who prefer the single origin view, the difference in the estimated timing is still a problem and some biochemists are suggesting that the descendants of `Mother Eve' wholly replaced other hominids such as Java Man and Pekin Man. Others counter that there could have been a replacement of the mtDNA in the population through inter-breeding and limits to population expansion, without wholesale extinct-ion of the earlier inhabitants. Evid-ence for a population bottleneck would be needed to support this latter view.

The family tree that has been constructed from the work on mtDNA is very unlike the family tree that would be built up after a visit to a place such as Lancaster House in London in search of one's own ancestors. The differences that occur between types of mtDNA are used to construct a `so called' family tree rather like one might do from looking at photographs of one's living relatives and trying to match up the relationships. Instead of the typical upside-down Christmas tree shape, the mtDNA tree is more bush-like or it could be better described as a rather uneven table supported on many legs. It would appear that at some time in the past there was a sudden explosion of different types from a very small population, followed by very little subsequent change.

This can best be explained by the scattering of a small population, into smaller, isolated groups across the world from which the present world population developed more or less in isolation since that time. This makes it very difficult to pin-point the original population because the migrations from the original site would have depleted the original gene pool so that the oldest population would not necessarily be the most diverse.

In the original scientific publication on evidence from mtDNA, the authors suggested that Africa was the site of origin of modern man. This was because the greatest differences between populations were within one wholly African line. It was concluded that this population must be the oldest as the greatest amount of time must have passed to acquire the most variability. However, recent technical reviews of the statistical methods used to analysis of the results cast doubt on the certainty of the proposed African origin. The computer analysis of the results used to construct the most likely family tree may produce millions of equally likely pathways. The trees from not just one run but many runs should have been considered for statistical correctness and it was also considered that the 100 `family trees' evaluated from just one run were not sufficient. The upshot of this recent debate is that an African origin proposed on the basis of mtDNA cannot be ruled out at this stage but it is by no means certain.

Although we might like to argue about the timescales, and the author of this article favours a more recent origin than the estimate of 75,000 years given from work on mtDNA, the Bible-believing Christian would wholly concur with the idea of a rapid growth in world population from a small number of individuals. At the time of Noah, the human race was clearly an `endangered species' , but it subsequently multiplied in the area around Babel. The present pattern of variation can then easily be accounted for by the incident at the tower of Babel when God terminated the building of the tower, confused the languages of the people and disseminated the inhabitants of that land across the world. These groups would have formed small, isolated communities, eventually populating the whole earth. There would have been much potential for population growth in such a sparsely inhabited earth if the climate and soil were favourable, but little opportunity for intermarriage between groups. These are the conditions necessary for the development of the `up-turned table' type of family tree. The arguments regarding the site of origin of modern man are difficult to resolve because many possible pathways can be constructed even from the 147 individuals in the original study. However, it should be noted that no individuals from the Middle East and the area of the Ararat massif were included in this work.

The present scientific information available from work on mtDNA, although not all the conclusions drawn from it, can be entirely reconciled with the Biblical account. Noah's family, being the sole survivors of a previously large population, colonised a particular area, increased in numbers, and then migrated simultaneously in many different directions following the Tower of Babel. The relatively small amount of change since that migration can easily be explained by contracting the time span of 75,000 or 190,000 - 240,000 years to a much lower figure. Far from being incompatible, a recent origin of less than 10,000 years for man is likely to be entirely supportable from the present scientific facts.

Nancy M. Darrall (1992)