
Mutations in Y Chromosome made us separate species from Neanderthals - technotony
https://www.newscientist.com/article/2083381-missing-y-chromosome-kept-us-apart-from-neanderthals/?utm_source=NSNS&utm_medium=ILC&utm_campaign=webpush&cmpid=ILC%257CNSNS%257C2016-GLOBAL-webpush-Y-CHROMOSOME
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thedevil
A little dark hypothesis:

I've seen some (intertwined) hypotheses in the news lately of why there's no
neanderthal Y chromosomes: the mixed-race-neanderthal-Y boys didn't do so well
for some reason, the human Y chromosome had advantages, or the neanderthal-Y
wasn't compatible genetically.

How about the more obvious guess: homo sapiens invaded and conquered
neanderthals, killing all the males (and their Y chromosomes with them). It's
speculative, but it would definitely not be the first time in history that
such a thing has happened. And the neaderthals live for hundreds of thousands
of years, then disappear just tens of thousands of years after homo sapiens
show up in their neighborhood. So it's likely one group wiped out the other.
And it's not hard to imagine keeping the women when you decide to kill a whole
neighboring tribe.

I actually came up with the hypothesis about how the two groups most likely
interbred just a few days before I found out in the news that the neanderthal
Y-chromosome disappeared. I don't know if I should be excited or disgusted
that the evidence might support my hypothesis.

~~~
danieltillett
Human history is unfortunately littered with stories like this, but we know
the Neanderthal genetic flow came in from the males. The reason why we know
this is we are missing all Neanderthal mitochondrial DNA sequences which are
only inherited down the female line. If your theory was correct then we would
see modern humans with Neanderthal mitochondrial genomes.

It appears what happened is much more interesting - Neanderthal males mated
with female humans of African origin, but the male offspring were infertile.

~~~
thedevil
Thank you for the insight. I wonder, how do we know the males were infertile?

~~~
danieltillett
We don't - all we know is that the Neanderthal Y chromosome is missing from
the modern human population. This could have occurred by chance (genetic
drift), lethal genetic incompatibility (all males died), or infertility. Given
the data we have it is hard to know which of these is the real cause.

~~~
thedevil
Is it not equally likely the other way around - that the Neanderthal
mitochondria disappeared because of unsuccessful mixed females or other
genetic drift?

~~~
danieltillett
No because of the way genetics works it is much more likely to be the Y
chromosome that is lost. First the Y chromosome is under stronger indirect
selection than the mitochondria due to asymmetric mating. Second in mammals
when two different species have a genetic incompatibility this incompatibility
manifests in the male offspring. Both of theses point towards male Neanderthal
female African as the way this hybridization happened.

Edit. I should add the scientific paper behind this New Scientist article
proposes a precise genetic mechanism for how the Neanderthal Y chromosome is
lost which is further evidence the loss is due Y Chromosome incompatibility.

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adaml_623
The title on NS is: "Missing Y chromosome kept us apart from Neanderthals" and
that is importantly different from the title here on HN.

Only males have Y chromosomes so if only "Mutations in Y Chromosome made us
separate species from Neanderthals" then female Homo Sapiens and Neanderthals
would be genetically the same. I know I'm being a bit pedantic about the use
of the word 'made' in the title but it seems important to me.

~~~
danieltillett
It is not that Africans females and Neanderthals are genetically the same,
just that the genetic incompatibility between the two species appears to be
sex specific. This is pretty common when different species hybridise.

Haldane's rule covers why this occurs [1].

1\.
[https://en.m.wikipedia.org/wiki/Haldane%27s_rule](https://en.m.wikipedia.org/wiki/Haldane%27s_rule)

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jessaustin
Actual study (open access!):
[http://www.cell.com/ajhg/abstract/S0002-9297(16)30033-7](http://www.cell.com/ajhg/abstract/S0002-9297\(16\)30033-7)

Many of the shortcuts taken in TFA seem to lead to confusion rather than
understanding, so this might be worth a read.

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danieltillett
I think someone needs to tell New Scientist that many of us are part
Neanderthal.

~~~
cauterized
Given that much of the definition of speciation these days is the inability to
produce fertile offspring with high likelihood, it sounds like they're right
on the nose.

Something like one mule (horse-donkey hybrid) in tens of thousands is fertile,
having by chance received just the right combination of chromosomes to be able
to reproduce. But the rest are sterile. The rare successful interbreeding
doesn't make horses and donkeys the same species either, despite being closely
related. (In their case, IIRC, the infertility of hybrids has to do with
differing chromosome counts between horses and donkeys.)

So we can have some Neanderthal genes (whether from prior to y-chromosome
differentiation or from the rare successful interbreeding or from successful
and fertile but rare female offspring) but still be separate species.

Besides, it's oft cited that we share 98% of our DNA with chimps, and nobody's
claiming that we're the same species.

~~~
danieltillett
The definition of a species is not the inability to produce fertile offspring.
Certainly if you can't produce fertile offspring then you are a different
species, but having fertile offspring does not mean you are the same species.

Many humans (all non Africans) are a hybrid between two different species -
all this result is telling us is that Africans and Neanderthals really are two
different species.

~~~
euei3i3i
You've made this claim before. It's so extraordinary that either we all would
have learned it in school or Nature would have published it and in addition it
would have been in all the major media.

Claiming that blacks are a different species, not even a different race, is
some next level Hitler / KKK / etc. shit.

But basically, I just think you don't know what you're talking about. For
example, I just typed "species" into my search box and Google handily provided
the following from Wikipedia:

> A species is often defined as the largest group of organisms in which two
> individuals are capable of reproducing fertile offspring, typically using
> sexual reproduction.

Go try and fix Wikipedia if you wish to spread nonsense.

~~~
mdellabitta
> Claiming that blacks are a different species, not even a different race, is
> some next level Hitler / KKK / etc. shit.

I may be missing something, but the claim I've read around the Internet is
that "Africans" are the only pure Human group, and are a different species
from _Neanderthals_ , while other Human groups have a small percentage of
Neanderthal genes.

Whether that's true or not, it seems like a far less problematic claim than
the one you mention.

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patall
I am reading about this story for a while now and still do not get what is so
surprising about it. While people of caucasian descent all share about 2% of
their DNA with the Neanderthals, thats all random bits and not a single larger
fragment or even chromosome. The latter would need to happen for the Y
Chromosome. All Chromosomes but Y (and Mitochondria) can exchange fragments
with their homologs but as there is always just one Y chromosome in any given
cell, thats is not going to happen there. Therefore, if we should find it, we
would find a whole Y Chromosome. But that is not going to happen. And that is
honestly not very surprising...

~~~
sokoloff
> While people of caucasian descent all share about 2% of their DNA with the
> Neanderthals

That number is shockingly low to me, which probably means I misunderstand some
subtlety of what you're saying. Could you expand/explain? (I'd have expected a
figure starting with at least two 9s [99+%])

~~~
loudmax
Modern Europeans share about 2% of their alleles with Neanderthals might be a
more correct way to put it. But to understand that sentence, you have to
understand what's an allele (and I'm not completely sure I'm using the term
correctly).

~~~
danieltillett
This is pretty close. A simpler way of describing this is 2% of the average
genetic heritage of a European is able to be traced back to Neanderthals. This
is a lower bound and it may be higher.

The more interesting observation is that the 2% is not the same 2% in everyone
of a European genetic background. Overall at least 25% of the Neanderthal
genome is present across the whole population.

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drpgq
Reading about things like this, I wonder about the fertility between groups of
modern humans that split the farthest back. Admittedly it isn't 600,000 years
ago, but I suppose there would have to be some problems.

~~~
danieltillett
Apparently is it common for there to be issues with teeth when individuals
from different genetic lineages have children. The genes that control teeth
size and location have some level of incompatibility that manifests itself in
orthodontist’s vacation homes.

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islon
Took me a few seconds and some stares to my dutch friend until I realized I
read "Netherlanders" and not "Neanderthals"

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astazangasta
This is fucking dumb. Drift is far more likely by orders of magnitude. New
Scientist is like the Gawker of science journalism.

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JoeAltmaier
Overstated. The article just says the genetic change is "linked to increased
risk of miscarriages ".

