WHERE YOU AND I CAME FROM
There are two competing theories to explain how mankind spread across the globe.
One suggests that between 100,000 and 200,000 years ago modern man (Homo sapiens) emerged from Africa to slowly populate the rest of the world, replacing any species of human that were already there. This is
known as the Out of Africa hypothesis.
The other theory suggests that modern humans arose simultaneously in Africa, Europe and Asia from one of our predecessors, Homo erectus, who
left Africa about two million years ago.
In recent years, support for the Out of Africa theory has come from the study of DNA in mitochondria, the energy-generating structures that reside just outside a cell's nucleus. This
mtDNA, as it is known, is inherited only from females. It also mutates - errors appear - at a steady rate, meaning it can be used as a "molecular clock" to investigate human history. Critics argued such analysis was based on a
small section, about 7%, of the mtDNA and this might cause problems in determining the genetic distance between individuals. With the data
available it was not possible to trace the mtDNA lineage back to sub-Saharan Africa, they argued.But during 2000, researchers at the University of Uppsala in Sweden have lessened
these reservations by initiating an analysis of the complete Mitochondrial genomes of their subjects. The new analysis suggests the three deepest branches on the new mtDNA family tree all go back to sub-Saharan Africa and there is another
branch that contains both African and non-African mtDNA.
What seems particularly significant is that the amount of mtDNA diversity among Africans is more than twice as great as the diversity seen
among non-Africans. The data the team gathered also indicated that there was evidence of a "population bottleneck" when the number of humans fell to a low level. It happened about
40,000 years ago when there could have been as few as 40,000 humans
The researchers may have also identified the stock of people from whom all non-Africans descended. They found that a group of six African (mtDNA) sequences are genetically distant
to those of other Africans, but share a common ancestor with non-Africans. These lineages represent descendants of a population that evidently gave rise to all the non-African
lineages. Based on these studies, our most recent common ancestor is thought to be a woman who lived in Africa some 143,000 years ago, the so-called Mitochondrial Eve.
In other words you can ultimately trace every female lineage back to a single Mitochondrial Eve who lived in Africa
Further support came for the theory from scientists from eight countries who drew up a genetic family tree of mankind by studying variations in the Y chromosome of more than a
thousand men from different communities around the world. The Y chromosome is one of the two sex chromosomes (X and Y) which only men carry (women carry two X chromosomes). To find the common paternal ancestor,
they mapped small variations in the Y chromosomes of 1,062 men in 22 geographical areas, including Pakistan, India, Cambodia, Laos, Australia, New Guinea, America, Mali, Sudan, Ethiopia and Japan.
However the findings raises new questions, not least because our most recent paternal ancestor (The ancestor of all males living today was a man who lived in Africa around 59,000 years ago)
would have been about 84,000 years younger than our maternal one. The scientists believed that this anomaly was the consequence of the human genetic blueprint
evolving as a mosaic, with different pieces of modern DNA emerging and spreading throughout the human population at different times. But the crucial point is that the two
studies show that although that there are different evolutionary histories for each region of the genome they all place the ancestor of all modern humans alive today in Africa."
Additional research published in the journal Nature Genetics in April 2000 gave an insight into the migration our ancestors made from
eastern Africa into the Middle East, then to southeast and southern Asia, then New Guinea and Australia, and finally to Europe and Central Asia. Some modern-day men living in what is now Sudan, Ethiopia and southern Africa are believed
to be the closest living descendants of the first humans to set out on that great journey tens of thousands of years ago.
With regard to Europe Bryan Sykes, Professor of Human Genetics at Oxford University states that everyone in Europe is descended from just seven women. Calling them "The Seven Daughters of Eve",
Professor Sykes arrived at his conclusion by studying Mitochondrial DNA, from 6000 random samples, and allowing for naturally occurring mutations, he established seven different clusters of DNA.
and so it follows that the seven clusters must have sprung from one woman each, 99% of Europeans can now be traced back to these seven women The discovery also reinforces the theory that
modern human beings have their origins in ancient Africa. Professor Sykes found that the seven ancestral mothers have strong links to one of three clans that still exist in Africa today.
This page was last updated on 11/01/23 10:27