Yo Daddy Was a Neanderthal
This Insult May Have Some Truth in it for Europeans and Asians
A new study out has figured out about 60% of the letters of DNA from three different Neanderthal bones. It is amazing how much a scientist can learn from a long extinct relative.
First off, it looks like there was some interbreeding between species at some point. By comparing human and Neanderthal DNA, scientists can tell that around 1-4% of European and Asian DNA came from Neanderthals. And it looks like Africans have no Neanderthal DNA at all.
So easy someone of European
descent can do it.
This is just what might be expected if there was interbreeding because Neanderthals and Africans probably never met. All the evidence so far points to Neanderthals living in Europe and Asia and not in Africa.
Second the scientists were able to use the Neanderthal DNA to try to figure out what makes a human different. They found 212 regions that underwent quick changes (called sweeps) since Neanderthals and humans split. Further investigation of these regions might reveal more about what makes a human a human.
Third they looked for specific changes in the DNA that were unique in humans. They found only 78 that had a big impact on the DNA within genes. Of these, three had to do with skin color suggesting this has been a big area of change for humans.
The scientists also found over 200 differences in human DNA that may affect how human genes work. More work needs to be done to figure out what effect these changes have on nearby genes.
Finally, and most importantly for future studies, the scientists were able to do these experiments at all. They took 30,000-40,000 year old bones, pulled out the bit of DNA that was left and figured out 60% of Neanderthal DNA. Think back on how hard it was to figure out the DNA from a live human ten years ago!
By working out the conditions for these sorts of studies, scientists will be able to figure out the DNA of many more extinct plants and animals. Considering how much they have learned about humans from these few bones, scientists will undoubtedly learn a whole lot more from additional studies like these. Keep an eye out for more results soon.
Getting Busy with Neanderthals
Modern humans started out in Africa. About 100,000 years or so ago, groups of these humans began leaving for the Middle East.
These groups then continued to spread across Europe, Asia and Australia and eventually to the Americas. But they weren't spreading into places without human relatives, just to places without humans.
See, groups of Homo erectus had left Africa around 1-2 million years before and settled the world. Each group evolved along a slightly different pathway depending on the local environment, chance, etc. One of these groups evolved into Neanderthals.
Scientists have been arguing about the history of the human race for a long time. One idea, called the Multiregional Model, argues that after Homo erectus left Africa, each group evolved separately into modern Africans, Asians, Europeans, etc. The second model, Out of Africa, argues that humans evolved in Africa and then wiped out the other groups. Most scientists today support the Out of Africa model.
As with a lot of science, reality is probably a bit more subtle than either of these extremes. In fact, reality is probably more like the Middle Ground model. What this model argues is that humans evolved in Africa but that there was some interbreeding between humans and the other species. This interbreeding is part of the reason for the different ethnic groups that are alive today.
Not much earlier research supported the Middle Ground model. Scientists looked at fossils and could find very little support. There was a Portuguese Neanderthal skeleton that suggested interbreeding but it was just one fossil. And looks at mitochondrial and Y DNA showed no evidence of interbreeding.
But of late, two key pieces of data have come out that support interbreeding. Back in April 2010, researchers looked at over 2000 different people's DNA. When they analyzed the DNA, the best explanation they could come up with for what they saw was that humans and Neanderthals had interbred significantly twice. The first time was 60,000 years ago in the eastern Mediterranean and the second was about 45,000 years ago in eastern Asia.
The second piece of data is more direct than this and is the focus of this article. In this study, scientists directly compared Neanderthal DNA to human DNA and saw regions of Neanderthal DNA in European and Asian DNA. But they didn't see the reverse"Šthey didn't see human DNA in the Neanderthal DNA.
This means that humans and Neanderthal interbred but it was a one way street in terms of DNA. The Neanderthal DNA took hold in humans but not vice versa.
This kind of thing is possible if there is a colonizing group overtaking a settled area. Basically the humans had babies with the Neanderthals and these babies grew up and went on to colonize further into Neanderthal territory.
In these circumstances, the Neanderthal DNA in the human DNA would have a chance to settle in as half-Neanderthals had babies with other half Neanderthals. And these hybrids went on to dominate the colonization of Europe and Asia. The native Neanderthals died out before human DNA could take a hold.
So Europeans and Asians have a bit of Neanderthal in them. It'll be interesting to see if these regions have any advantage for the humans that have them. And maybe those Geico ads will have to be changed to, "So easy a European can do it."
Wheat from Chaff
Figuring out 30,000 year old DNA is no walk in the park. There isn't a lot of it there. And the bit that remains is degraded and parts of it are chemically changed.
If this were the only problem, it wouldn't be so bad. But scientists have to contend with contaminating DNA too. There is lots of DNA from bacteria that colonized the bone after the Neanderthal died. The researchers also have to deal with keeping their own DNA away from the Neanderthal DNA.
This last point isn't as important if a scientist is looking at an ancient tree's DNA. Its DNA will be different enough from human DNA that the scientists will be able to distinguish the two. Neanderthal and human DNA are very similar though. So similar that they can be hard to tell apart.
What all of this means is that researchers had to come up with ways to just look at Neanderthal DNA. And they had to come up with ways to decipher what they found.
The researchers found ways to chop up bacterial DNA that mostly left the Neanderthal DNA alone. They also worked under clean room conditions to keep their DNA away from the Neanderthal DNA. They used a variety of techniques to show that they had a contamination rate of about 1% for modern human DNA. This is low enough to overcome in their analyses.
So they now had Neanderthal DNA. The next step was to try to decipher it given how beat up it was.
Just like in human cells, the most common problem with the Neanderthal DNA is C's turning into T's. Remember, DNA is made up of four "letters" -- A, G, C, and T. When scientists compare two DNA's, it is the order of these letters that is being compared.
This means that if a lot of C's turn into T's, then there is going to be a lot of mistakes. Which means the scientists won't have a true readout of the Neanderthal DNA.
Luckily scientists know about this problem. And that it happens more at one end of the DNA than at the other end. Scientists can use this information to correct the results.
For example, scientists can read both strands when figuring out DNA. Remember, DNA has two strands and that A always lines up with T and G with C. So if a scientist finds a TG pair, then that scientist can conclude that the pair was actually a CG pair. This is because the best explanation for the GT pair is that the T used to be a C.
With these tools, scientists were able to figure out the Neanderthals' DNA. Next they will need to figure out the DNA of more fossils to learn even more about what it means to be human. And who our relatives were.