Scientists have uncovered what, for some couples, may be an uncomfortable truth: all people of European descent are related.
Go back a few generations and even people from opposite ends of the European continent share common ancestors, according to a new study of genome data published in the journal PLOS Biology.
Researchers from the University of California, Davis, conducted what they described as one of the first surveys of recent European genealogical ancestry over the past 3000 years.
"We detected 1.9 million shared long genomic segments, and used the lengths of these to infer the distribution of shared ancestors across time and geography," the scientists wrote in their paper.
"We find that a pair of modern Europeans living in neighbouring populations share around 12 genetic common ancestors from the last 1500 years, and upwards of 100 genetic ancestors from the previous 1000 years."
The researchers concluded that "individuals from opposite ends of Europe are still expected to share millions of common genealogical ancestors over the last 1000 years".
Co-author Graham Coop from the University of California, Davis, said the study focused on Europe. "While it is likely true that all humans world-wide likely share all common ancestors a few thousand years ago, we can only demonstrate this in Europe so far," he said.
Associate Professor Darren Curnoe, a human evolution specialist at the University of New South Wales, said the findings should be a major pause for thought.
"This research greatly reinforces the idea that we living humans are all exceptionally closely related, no matter where we live today or our perceptions of our ancestry," said Dr Curnoe, who was not involved in the study.
"Bigotry based on 'race' should be seen for what it is, completely divorced from biological reality. We all share very recent direct ancestors no matter where you come from."
The new findings also apply to Australians of European heritage, he said.
"We can all trace our immediate ancestors back only a handful of generations, only a few thousand years. The differences we think we see are remarkably superficial and largely biologically meaningless," he said.
"If your ancestors are from a relatively small part of Europe, especially say Eastern Europe, then all of your direct genetic ancestors may have lived only in the last thousand years. For the whole of Europe, this might be just a few thousand years."
Professor Maciej Henneberg, Wood Jones Professor of Anthropological and Comparative Anatomy at the University of Adelaide said the findings mean that "all Australians of European heritage are closely related and there is no use distinguishing between Australians of English or Irish ancestry and those of Greek or Italian heritage."
"Biological anthropologists have argued for the last 50 years that human species cannot be divided into "races" because all humans are so closely related that there is not enough difference between gene pools of people living in different continents to produce reliable biological distinctions between Africans, Europeans, Asians and so on," said Professor Henneberg, who was not involved in the study.
"The few externally visible differences like skin colour or nose shape are not enough to justify divisions."
Professor Henneberg said it was no wonder all Europeans were related.
"In a densely populated continent, genes travel through neighbourly contact. In one generation, somebody marries someone from the next village, in the next, a person from that village marries somebody from yet another village further away and so on," he said.
"This way, with nobody moving more than 20 kilometres in a generation, a gene can travel about 2000 kilometres [the distance from Berlin to Madrid] in 3000 years."
Sunanda Creagh is news editor at The Conversation and a former Sydney Morning Herald and Reuters reporter.