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 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. The researchers believe all humans alive today could share common ancestry with a being in Africa who lived about 120,000 to 220,000 years ago.
30th October 2000
The most recent ancestor of all males living today was a man who lived in Africa around 59,000 years ago, according to an international team of
The scientists from eight countries have drawn 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).
The new research confirms the Out of Africa theory that modern humans originated in Africa before slowly spreading across the world.
But the finding raises new questions, not least because our most recent paternal ancestor would have been about 84,000 years younger than our
maternal one. The team believes there is an explanation. They propose that the human genetic blueprint evolved as a mosaic, with different pieces of modern DNA emerging and spreading throughout the human population at different times.
Origins of man
Evidence from the fossil record suggests that modern man originated in Africa about 150,000 years ago, before moving steadily across the globe.
This Out of Africa hypothesis has been confirmed by studies of mitochondrial DNA, the segment of genetic material that is inherited exclusively from the mother. 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.
To find the common paternal ancestor, the team drew up a genetic family tree of mankind. 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.
The new genetic family tree supports the Out of Africa scenario. But it suggests that our most recent paternal ancestor would have been about 84,000 years younger than our maternal one.
Regions of the genome
"You can ultimately trace every female lineage back to a single Mitochondrial Eve who lived in Africa about 150,000 years ago," said Dr Spencer
Wells of the Wellcome Trust Centre for Human Genetics in Oxford, UK, who was part of the team.
"The Y chromosome we trace again back to Africa but the date is about 80,000 years ago. He told BBC News Online that the two studies
could be reconciled. "There's a different evolutionary history for each region of the genome but they all are consistent in placing the ancestor of all modern humans alive today in Africa."
The research, published in the journal Nature Genetics, gives an intriguing insight into the journey of our ancestors across the planet, 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.
19th April 2000
Everyone in Europe is descended from just seven women. Arriving at different times during the last 45,000 years, they survived wolves, bears and ice ages
to form different clans that eventually became today's population.
These are the claims of Bryan Sykes, professor of human genetics at Oxford University. Calling them "The Seven Daughters of Eve", Professor Sykes has individually named them Ursula, Xenia, Tara, Helena, Katrine, Valda and Jasmine. Professor Sykes arrived at his conclusion by studying mitochondrial DNA, which is passed down from mothers to children. From 6000 random samples, and allowing for naturally occurring mutations, he established seven different clusters of DNA. "It follows that the seven clusters must have sprung from one woman each," he told the BBC. Professor Sykes says that the ancestry of
99% of Europeans can now be traced back to the seven women who founded the clans. He has also been quick to realise the commercial
aspects of his project, founding a company,Oxford Ancestors, which offers to trace anyone's maternal ancestry for £120.
However, Professor Sykes went on to say that whilst his genetic work is rooted in fact, the names he has given to the women are hypothetical. He says the names are an attempt to personalise DNA codes, which have traditionally been labelled alphabetically.
"For example, with the letter T, group T, I've just extended that to be the descendants of a woman called Tara," he said.
The study is being seen as further evidence of the way in which genetic research can shed light on human history. His names for the women, which draw on Gaelic, Scandinavian and Persian heritage amongst others, reflect the huge geographic area from which modern Europeans descended.
His 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.