DNA Traced back to one woman

It turns out that DNA science supports the idea that we all really do share the same ancient mother. Here’s why everyone on earth is actually linked back to this one woman in Africa.

Homo sapiens is the only human species alive today and after testing thousands of living people we can show that the oldest mitochondrial DNA sequence comes from a common ancestor of us all – “mitochondrial Eve”.

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How are we all related to one woman/female ancestor?

The piece of Eve’s DNA that has been traced comes from something called the mitochondria – it’s in all human cells. There is DNA inside the mitochondria, and it’s this DNA that has been traced back all the way to Eve - some 150-200,000 years ago, and is of African origin (sub-Sahara), probably from Ethiopia or Kenya.

How come our direct maternal lineage does not go back further than Eve?

The species Homo sapiens is older than 200,000 years but - this is the hard part – ‘Eve’ is dated back to Africa about 150 to 200 thousand years ago.

We know this because analysis of variation in living humans, plus the mutation rate in mitochondrial DNA, permits us to calculate when the ancestor of all living mitochondrial DNA chromosomes was alive.

Prior to ‘Eve’, there were actually still many females living, but all those lines (other than Eve’s own direct ancestor) have died out. Some will have died after a hundred, some thousands, some tens of thousands of years.

Remember, for the lineage to survive to today, a female must have a fertile daughter, who in turn has a daughter over 8,000 generations.

Mitochondrial Eve: the one ancient female ancestor from whom we are all descended (Illustration by Matt Roden) (SBS)

By Illustrations: Matt Roden

18 MAY 2016 - 2:42 PM UPDATED 19 MAY 2016 - 3:06 PM

What are “mutation markers” and how do they trace back to Eve through our DNA?

A mutation is any change in the DNA sequence. These alterations or mutations occur by chance and are, therefore, random.

If a mutation arises on the Y chromosome, or on our mitochondrial DNA, and it does not kill us, it will be passed to the offspring.

So these mutations can be traced back through the generations by analysing the Y chromosome ancestry of an individual’s direct father’s line, and therefore can only be performed on males.

Mitochondrial DNA is the equivalent for tracking the direct maternal ancestry as it is passed through females. In this way, we can trace the direct maternal and paternal ancestries of males.

When a new mutation occurs and ‘branches off’ from the line, it’s called a branch.

A mutation, which became known as the M branch, arose around 70,000 years ago and there have been very many further mutations of people belonging to the M branch over time, so that today there are many, many sub-branches within the ancient M branch.

All these sub branches share the common M ancestor: a woman in who lived approximately 70 thousand years ago.

How we can trace Genghis Khan’s DNA through the Y Chromosome?

Analysis of Y chromosomes in Asian men showed the spread of a Y lineage that can be explained by a historical fact – the spread of the Mongol empire under Genghis Khan and his descendants.

This particular Y lineage was found from the Caspian Sea to the Pacific and accounted for approximately 8% of the Y chromosomes in the region.

The time to the most recent common ancestor of these Y chromosomes was estimated to be approximately 1000 years and Mongolia was the clear source of the Y chromosome. This data is consistent with the hypothesis that they represent the Y chromosome of Genghis Khan, his immediate male relatives, and all their descendants.

DNA Nation airs Sunday 8.30pm on SBS from 22 May.

Watch a trailer for DNA Nation below:

Dr John Mitchell is a human geneticist who is also the series consultant for DNA Nation and will act as a guide to intrepid adventurers Ernie Dingo, Julia Zemiro and Ian Thorpe throughout the show.