Adam and Eve in the garden of eden

Meet your (distant) cousin

All humans are related to one another – and to all other living organisms

If you have an unusual surname, you are probably related to other people with the same name. Travel back farther in time, and your distant ancestors will link you with hundreds, thousands or perhaps millions of different people.

Go back 11 generations and you had more than 2,000 ancestors; if each of them and all their descendants had two children, you would have more than a million living relatives (assuming no interbreeding).

Go back further still, 40 generations (around 1,200 years), and you would have a thousand billion potential ancestors – far more than the world population. So these potential ancestors were not all different people.

Some estimates suggest that the most recent common ancestor of all humans alive today lived just a few thousand years ago.

Go back even farther, and your ancestors would begin to resemble apes, then small pig-like mammals, then fish-like creatures hauling themselves around on sturdy limb-like fins, and so on back to the very first forms of life, from which all living things are thought to have evolved.

Everything that lives today, or has ever lived, is a member of the same big family.

The genetic ties that bind

The idea of tracing genetic information back through past generations has led to the ideas of mitochondrial Eve (see our article on ‘her’ for more) and Y chromosome Adam.

Mitochondrial DNA is inherited from mother to daughter. By comparing global mitochondrial DNA sequences, it is possible to identify what the last common ancestor of all present-day sequences would have been and when it existed. This is the hypothetical mitochondrial Eve – the last woman from whom all women now living are descended.

Mitochondrial Eve is likely to have lived in East Africa 100,000–200,000 years ago, before Homo sapiens migrated out of Africa.

Similarly, Y chromosome Adam is the earliest male human that all current Y chromosome lineages can be traced back to (the Y chromosome being passed from fathers to sons). The Y chromosome is much bigger and more complex than mitochondrial DNA and is being intensively studied. The date when Y chromosome Adam lived is thus highly uncertain and subject to regular revisions.

Curiously, Y chromosome Adam may not have been around at the same time as mitochondrial Eve, although a 2013 analysis dated Adam to between 120,000 and 156,000 years ago and Eve to between 99,000 and 148,000 years ago.

Lead image:

Lucas Cranach/Flickr CC BY


Further reading

About this resource

This resource was first published in ‘Evolution’ in January 2007 and reviewed and updated in December 2014.

Cell biology, Genetics and genomics, History
Education levels:
16–19, Continuing professional development