MyWeku

Many people occasionally think about where they came from. When they do, they think mostly about their parents, grandparents and great-grandparents. This is where the trail runs out for most folks, unless they have done some research into their ancestry. This article skips a couple of thousand of those inconvenient, hard to research generations and reaches back to the two common ancestors of every single person reading this article. Moreover, it reaches back to the common ancestors of every single human on the planet. It would be tempting to call our two common distant ancestors Adam and Eve but, as you will see, they bear very little resemblance to the characters portrayed in any religious account.

Some 99% of the human genome is mixed up at each new birth. In fact, the whole biological purpose of sexual reproduction is to ensure that the gene pool is constantly being shuffled up like a pack of cards. The other 1% of the genome, however, remains intact and within this 1% there are distinct gender-specific types of genes.

In men, the part of the Y chromosome which does not link with the X chromosome gets passed unchanged directly from father to son.  In women, the story is a little more complicated. The unchanged female DNA is found within mitochondria which exist in human cells outside of the nucleus. The mitochondria are echoes of the DNA of bacteria which formed a symbiotic relationship with the ancestors of humans approximately two billion years ago and still today carry original genes. When a sperm fertilises the egg in human conception, the male mitochondria are left behind in the tail of the sperm so only the mitochondria in the female egg cells survive to the next generation.

The only changes in these genes, therefore, will come from mutations. By working back through the mutations, like unravelling a tangle of string, geneticists are able to show how all humans developed from Africans. Also, the geneticists can estimate, with reasonable accuracy, how much time has passed until they get to the end of the string, that is, to the points at which all of the various mutations have been accounted for down both the male and female routes.  This is a complicated process which has only been made possible by modern computers statistically extrapolating the raw data.

From this research it appears that our common female ancestry narrows down through time to a female living on the African savannah approximately 150,000 years ago. Our common male ancestor was somewhat younger. He was also living in Africa some 59,000 years ago. These represent the last common ancestors we can trace genetically.

Common descendants of these two individuals proceeded to slowly expand out of their homeland usually to find new sources of food. Over the millennia they spread over ancient land bridges and across short sea crossings to Asia and Europe, adapting slowly to new living conditions and challenges as they went. We are all out of Africa. The differences between all of humanity, it would seem, are merely the mutations which took place in adapting to new circumstances in new environments.

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Photo Courtesy: Duncan Walker