[ExI] The Yamnaya question

Rafal Smigrodzki rafal.smigrodzki at gmail.com
Sun Jun 2 00:36:41 UTC 2019

On Sat, Jun 1, 2019 at 1:44 AM <spike at rainier66.com> wrote:

> If we go with this notion of optimal breeding distance, we can imagine how
> it would work with body-fat ratios, but even easier is to think about
> dentition.  My dentist friend was also an orthodontist.  I asked him once
> why it is that so many of us Euro-mutts seem to need braces.  His notion
> was a bit similar to yours: we are genetically made of so many disparate
> parts, populations which evolved under so many varying conditions and
> climates, we just have too much stuff in our genes, too many incompatible
> instructions.  So we have cases of gapped teeth up top and crowding on the
> bottom for instance in the same person.  We have jaws too large or too
> small for the teeth they have in them.

### I am not sure about the genetics of occlusion abnormalities but I would
guess that due to the recent and extraordinary changes in the types of
diets that modern humans have been exposed to (from paleo to early
agricultural to industrial in only a few thousand years) there is a lot of
genome-environment mismatch between our dental and metabolic
hunter-gatherer adaptations and modern lifestyles. I would however think
this is not related to increased mating distances in modern societies.

> In our times, we Euro-mutts, the Yamnaya descendants, are now drifting
> towards breeding distance that is too great.
> Rafal you really have my wheels spinning.  More ideas tomorrow perhaps.
### The theoretical notion of OMD was recently validated on a wide range of


and it looks like the OMD estimated in this article is about equal to the
genome-wide nucleotide diversity (π) which hovers somewhere around 1/2 of
the maximum genetic distance (Dmax), roughly similar between plants, fungi
and mice, so it may be a very general finding. It translates to about 4-6
nucleotide differences per 1000 nucleotides between each parent in mice. I
don't have the data on average nucleotide differences among Caucasians, or
between Caucasians and various other races. However, we can use times since
divergence to estimate the relationships between average nucleotide
diversities and Dmax for various groups.

For example, we know that H.sapiens and H.neanderthalensis hybrids were
viable, although the surviving Neanderthal DNA stretches show evidence of
strong purifying selection, which indicates high levels of genetic
incompatibility (see David Reich's book). Human and Denisovan hybrids and
human and an unnamed African subspecies were also viable. These other
subspecies, Neanderthals, Denisovans, diverged from humans sometime around
500,000 years ago (there are some new guesses putting the divergence at 800
k). We can use that date do estimate the Dmax.

On the other hand, we know that the Yamnaya diverged from the founding
groups in the past 5000 years (and the Anatolian and hunter-gatherer
European populations diverged around 10 - 15 k), so as a whole Caucasians
may have accumulated let's say 10 k years worth of divergence, which we can
use as an estimate of nucleotide diversity π.

It is clear that the nucleotide diversity among Caucasians (at 10k years)
is much lower than the Dmax implied by viable human-archaic hybrids (500k
years), so any crosses among Caucasians are very far from Dmax, and most
likely well below OMD. The Yamnaya expansion stirred our genes up and made
us less inbred, but probably not yet reaching the best level of
outbreeding, the OMD. If we take the above article at face value, the OMD
for humans might be equivalent to 150k - 200k years divergence but without
data on actual nucleotide diversities among humans it's just a rough guess.

It is however quite plausible that the mating distance between Caucasian
and South-East Asians might be closer to OMD. Caucasians and Asians split
50k years ago, still well below the 500k split that corresponds to Dmax, so
unlikely to overshoot OMD (see the hump curve in the article). If true,
this may explain the anecdotal evidence of Hapas being prettier and smarter
than either parental strains.

There is an interesting article on geographical exogamy (mating among
geographically distant humans) here:


Turns out that at least in the steppes of Asia it takes at least a distance
of 40 km between parents to even start reducing inbreeding. This would
support the idea I advanced in my initial post: humans in the pre-cavalry
age, who hardly ever traveled 10 miles from their place of birth, were
probably very inbred, and the Yamnaya with their hundred-miles mounted
sorties may have been able to stir the genetic pot a lot.
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