
How Neanderthal DNA Helps Humanity - Geojim
https://www.quantamagazine.org/20160526-neanderthal-denisovan-dna-modern-humans/
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tokenadult
The article is very interesting and informative, and comes from a good source.
But I have to quibble about describing Denisovan and Neandertal hominins who
were ancestors of current human beings as coming from a "different species,"
because by one of the main concepts of speciation, if two organisms can mate
and have viable offspring, and then the offspring can further reproduce, you
say the two organisms are part of the SAME species. There are, of course,
full-length books about the details of defining species among the common
descendants of the earliest living things, and about the mechanisms that bring
about speciation among the descendants of a common ancestor species,[1] but
right now we don't always know for sure when we dig up old hominin bones which
belong to relatives of direct ancestors of living human beings and which do
not--that is part of what the studies of ancient DNA are intended to find out.

To make the point I am bringing up here, I would rewrite the second sentence
of the helpful article kindly submitted here to read, "As the individuals who
provided the main genetic contribution to modern humans began to spread out of
Africa roughly 50,000 years ago, they encountered other hominin clades that
looked remarkably like them — the Neanderthals and Denisovans, two groups of
archaic humans that shared an ancestor with us roughly 600,000 years earlier."

[1] [http://www.amazon.com/s/ref=nb_sb_noss_2?url=search-
alias%3D...](http://www.amazon.com/s/ref=nb_sb_noss_2?url=search-
alias%3Daps&field-keywords=Speciation)

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grondilu
That conception of what a species is has been my understanding as well for a
long time. It's a very simple and clear concept but apparently biologists have
given up on it for various reasons. There's actually a whole wikipedia article
about it:

[https://en.wikipedia.org/wiki/Species_problem](https://en.wikipedia.org/wiki/Species_problem)

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Steko
Nothing in your link suggests they've all given up on the concept.

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grondilu
Not the concept itself, but the aforementioned simple and clear definition.

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jrapdx3
Based on prior discussions I've had the impression that the BNC2 and other
skin-related Neanderthal genes were associated with less melanin pigmentation.

Melanin reduces penetration of UVB into skin cells, important in an equatorial
environment to protect skin integrity. However in northerly latitudes, heavily
pigmented skin is a disadvantage due to the role of UVB exposure in producing
vitamin D, essential to survival.

Indeed the most pigmented skin requires 5 times the UVB exposure to produce
equivalent amount of vitamin D vs. least pigmented. A possible tradeoff for
adaptating to an environment with less available sunlight is greater
susceptibility to developing conditions like melanoma, but that's admittedly
an oversimplification of a very complex subject.

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danieltillett
The world map for Denosovian DNA is wrong. The Australian/Papua population is
around 6% not the 0.8% which the figure shows.

It is a shame that Africa is so ignored in these studies. We know that there
were many interbreeding events that occurred in Africa (the African pygmies
are one example), but we know almost nothing more.

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riffraff
> the African pygmies are one example

can you expand on this?

~~~
danieltillett
Sure. Have a look at this post [1].

1\. [http://dienekes.blogspot.com.au/2016/02/archaic-
introgressio...](http://dienekes.blogspot.com.au/2016/02/archaic-
introgression-in-pygmies.html)

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JoeAltmaier
The colored map is informative - color reflects percent of archaic genes
inherited by modern populations. But the placement of the colored dots looks
suspiciously like a heatmap. I know the data is sparse. But maybe there'd be a
better way to represent it.

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Ericson2314
The genome percentages in the article are a bit confusing. It is oft-quoted
that we are "99% Chimpanzee", so how could we also be no more than "6%
Denisovan"? Answer: they really mean 6 percentage points "realigned" vs the
African reference populations. I've read many other articles repeating the
"6%" and it would be nice if they (and this) were clearer (and used the
correct units--but maybe that's too much to ask).

Some cool charts for reference:
[http://www.scientificamerican.com/article/tiny-genetic-
diffe...](http://www.scientificamerican.com/article/tiny-genetic-differences-
between-humans-and-other-primates-pervade-the-genome/)

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danieltillett
The 99% is basically wrong. What it is referring to is that for 99% of genes
you can find in humans you can find an ortholog in chimps. It tells you
nothing about the function of the genes in the two species and is basically
meaningless from a functional perspective.

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Ericson2314
I'm no geneticist, but isn't this "structural" number still valuable for other
purposes? Also isn't the 6pp also "structural" so modulo my previous
complaints we're comparing like measurements?

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arcticfox
Out of curiosity, how do you take the modulo of an (English) argument?

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Ericson2314
[https://en.m.wikipedia.org/wiki/Modulo_(jargon)](https://en.m.wikipedia.org/wiki/Modulo_\(jargon\))
in ignoring the differences I already pointed out ("my previous complaints") I
am defining an equivalence relation.

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arcticfox
Cool, thanks

