Creation or Evolution: Do We Have to Choose? by Denis Alexander

Author:Denis Alexander
Language: eng
Format: mobi, epub
Tags: Evolution, Creation
ISBN: 9780857215789
Publisher: Lion Hudson
Published: 2014-09-18T22:00:00+00:00

Figure 16. The way in which our mitochondrial DNA is inherited from a single woman, the so-called ‘Mitochondrial Eve’. Only 15 generations are shown for the sake of simplicity. Note that there were many other women alive at the time of ‘Mitochondrial Eve’. but their lineages eventually died out.

Simply by drawing family trees on the back of an envelope we can easily show that the mitochondrial DNA of all the people alive in the world today must have originated from a single woman, the so-called ‘Mitochondrial Eve’ (Figure 16). It will be remembered that mitochondria are the cell’s tiny power stations, located outside the nucleus, and containing their own small portion of DNA. The term ‘Mitochondrial Eve’, much used in the popular press when the concept was first introduced in the 1980s, is a misleading one. It does not at all mean that this woman was the only female human alive at the time; it just means that female transmission with a large enough number of generations will eventually lead back to only one woman, by definition, who can be the origin of all mitochondria. Think of the ‘tattooed number on the arm’ illustration that we used above. As we work through many thousands of generations, eventually all numbers except one will fail to be transmitted, leaving a single number on the arms of a complete population. It is the last common ancestor to bear that number on her arm that then becomes the ‘Mitochondrial Eve’ in this illustration. But remember that the same mode of transmission does not apply in the case of the bulk of our DNA, the nuclear DNA, which undergoes extensive reshuffling in each generation as variant versions of DNA from both parents are combined.

Extensive investigations of mitochondrial DNA sequences from human populations around the world have revealed two fascinating insights into human evolution. The first is that the ‘genetic clock’ data point to the existence of a ‘Mitochondrial Eve’ in Africa who lived approximately 99,000–148,000 years ago according to one recent estimate,201 consistent with the fossil data for the emergence of H. sapiens described above. This finding provides strong support for the ‘Out of Africa’ model for human evolution that currently holds sway.202 Had there, for example, been extensive interbreeding between the H. sapiens populations and the more ancient H. erectus populations that overlapped extensively in time with H. sapiens, then much older dates for the putative Mitochondrial Eve would have been expected. The second important insight arising from human mitochondrial DNA sequence studies is that all non-African mitochondrial DNA from anywhere in the world is remarkably similar, whereas there are greater mutational differences between the mitochondrial DNA of different African populations. Sequencing of nuclear DNA from individuals coming from different parts of Africa makes the same point. The genetic diversity in the populations of non-African countries represents subsets of the genetic diversity found in African populations. In fact, many African populations now being studied seem to have lived separate from each other for 100,000 years or more.

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