DNA from modern humans and Neanderthals reveals ancient interbreeding of the two species.
As the success of family history TV programmes shows, we seem to be endlessly fascinated with our ancestors. But tracing your great-great-great-great aunt is nothing compared to what scientists have announced this week.
A pair of papers published in the journals Science and Nature, looks at how our Neanderthal ancestors have left genetic traces in our genomes today.
Modern humans, Homo sapiens, and Neanderthals split apart in Africa more than half a million years ago. But while humans stayed in Africa, Neanderthals went off to explore Europe and Asia.
When we finally left Africa less than 100,000 years ago, there's good evidence that these early adventurers interbred with the Neanderthals living between Western Europe and Siberia.
Comparing DNA from Neanderthal bones with our own tells us that around 2 per cent of the genomes of people descended from non-African populations is Neanderthal.
The Neanderthal genes are scattered across the genome, and different people have different ones. Previous research has pinned down a few of these, for example genes involved in responding to infections or UV radiation from the sun.
Now the new research, from two separate teams of researchers in the US, has looked at much larger parts of the modern human genome that probably came from our Neanderthal cousins, who died out around 30,000 years ago.
The scientists used computer programmes to pinpoint sequences in our modern DNA that looked like they were much older, and compared them with the Neanderthal genome to pick out regions that probably came from them.
One team of researchers found about one-fifth of the Neanderthal genome spread across the genomes of more than 600 currently-living Europeans and East Asians, while the others put together about 40% of the Neanderthal genome from the DNA of more than a thousand living people.
The data shows that while this interbreeding may have given our human ancestors useful genes for coping with the cold of northern Europe, the downside was that the Neanderthal/human hybrids probably had fertility problems.
There's also evidence that Neanderthals gave us gene variations linked to certain diseases, including type 2 diabetes, and depression, as well as immune system-related diseases such as lupus, biliary cirrhosis and Crohn's disease.
Curiously, the scientists also found that Neanderthals gave us smoking addiction, although this gene is probably involved in some other biological process, as there's no evidence at all that they liked to light up a cigarette in their caves.
Some genes are found in humans and not Neanderthals. One intriguing example is the gene FOXP2, involved in speech and language, which is in our DNA today but doesn't seem to exist at all in the Neanderthal genome.
There are also big chunks of the Neanderthal genome that are nowhere to be seen in our modern human DNA, suggesting these genes were harmful for us.
So far, the researchers have only looked at comparisons with Neanderthals and modern humans from populations that came out of Africa. But it would be interesting to look more closely at the genomes of modern Africans, as well as people all over the globe, to see if there's any more evidence of interbreeding with long-extinct populations way back in our family trees.
If Neanderthals could and did interbreed with sapiens then it becomes clear that they were not separate species after all. And since Australian aborigines are essentially homo erectus then that would mean they were not a separate species either.
The most recently announced research suggests that humans and neanderthals were right on the edge of being different species, and their offspring may have been of low fertility - similar to what happens when donkeys and horses breed, but to a lesser degree. This conclusion is based on the lack of neanderthal genes on modern human X and Y chromosomes.
Did the Neanderthals carry the Chromosome 2A/2B fusion?
The entire debate underlines the fact that "species" is not a defined term, any more than "race" is. We can assign living things to large arbitrary groups based on appearance but such assignments are of little predictive value. At the other end of the telescope we can in principle write down the entire genome for any individual, and this should be predictive, but in practice it is very difficult to do. alancalverd, Fri, 7th Feb 2014
Silly question really, if you examine Homo "Sapien" (wise ??? - does this mean educated or clever???) and its relentless use of genetic filters to select a mate at the primary point of instigational motivation to breed.
As much as interbreeding, i really can only see that as a .."Silly question really"... because even if there were fertility differences at least one of the two parties to this day has surviving offspring with the other so called species that did want to go(of which the FOXP2 has left someone speechless about it).
I read an article that said that while kittens meow to attract the attention of their mother, they don't meow to one another after a certain age, but they do meow to people. And it's odd, that my cat's meow has speech like inflections, going up at the end like a question when she wants something or is looking for me in the house, but other times sounding more like a statement or exclamation. cheryl j, Mon, 10th Feb 2014