Guide to Patagonia's Monsters & Mysterious beings

I have written a book on this intriguing subject which has just been published.
In this blog I will post excerpts and other interesting texts on this fascinating subject.

Austin Whittall

Friday, May 15, 2015

On when Humans and Neanderthals admixed

The journal Nature informs about a DNA analysis done to a jawbone found in a cave in Romania which could indicate a very recent admixture of Neandertal genes in humans:


"Qiaomei Fu, a palaeogenomicist at Harvard Medical School in Boston, Massachusetts, told the meeting how she and her colleagues had sequenced DNA from a 40,000-year-old jawbone that represents some of the earliest modern-human remains in Europe. They estimate that 5–11% of the bone's genome is Neanderthal, including large chunks of several chromosomes. (The genetic analysis also shows that the individual was a man). By analysing how lengths of DNA inherited from any one ancestor shorten with each generation, the team estimated that the man had a Neanderthal ancestor in the previous 4–6 generations. (The researchers declined to comment on the work because it has not yet been published in a journal)."

This apparently "questions the idea that humans and Neanderthals interbred only in the Middle East, more than 50,000 years ago.".

It makes sense, if your dad or mom were Neanderthal 50% of your genes would be Neanderthal, if one of your grandparents was a Neandethal, you would have a 25% share of their genes, and if it was your great-grandfather or great grandmother it would drop to 12.5%. So if it is 5 - 11% it sounds reasonable to imagine 4 or 6 generations.

Now if we consider that "All humans who trace their ancestry beyond sub-Saharan Africa carry a sliver of Neanderthal DNA — around 1–4% of their genomes." does this mean that we mated with Neanderthals 6 to 10 generations ago? The maths does not seem correct to me.

This dilution depends on how the mixture took place, it is not so straightforward as the article tries to make it appear. Allow me to explain:

Imagine a population of humans and Neanderthals mix equally, 10 men and 10 women, their children will be 50% human and 50% Neanderthal, if we keep them breeding among themselves and we assume no natural selection favoring any genes, after "n" generations they will still have 50% of each genome, that is, 50, 100, 1,000 or 10,000 years later they will still be 50-50.

However if we allow some additional 100% pure humans to mix with them each generation, this will dilute the Neandertal content and increase the Human proportion. Or, on the other hand, if they mix with pure Neanderthal each generation, the opposite will happen, the Neanderthal genes will increase over the human ones.

Then we mus add natural selection which may select against or for certain genes and alter their prevalence at a quicker or slower rate!

I could simplify and say : if current ratio of 1-4% means they intermingled 50kya. Then 5 -11% means they admixed 100 kya... can you prove me wrong?

I have the feeling that Homo sapiens are older than the currently accepted age, and so are Neanderthals, and that we did admix long before 40 or 50 kya.

We will have to wait for the paper to be published.

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