GENEALOGY-DNA-L Archives

Archiver > GENEALOGY-DNA > 2006-05 > 1147197059


From: John Lerch <>
Subject: Re: [DNA] Brown eyes
Date: Tue, 09 May 2006 12:56:05 -0500


One thing that no one has brought up in this debate--in an attempt to
answer Ken's guesstimate that blue eyes took over in a number of regions
despite numerous influxes of brown eyes and therefore must have some
selective advantage--is the evolutionary hypothesis: There is an
advantage to recessive visual aspect gene characteristics since it can
help prevent fathers from disavowing there children. IOW there is a
selective disadvantage to the dominant gene. Of course at some point
that loses its advantage as too many candidate lotharios also have blue
eyes/ pale skin etc.
There is also an advantage to blue eyes that in a certain light is a
disadvantage--it allows the viewer to see the degree of pupil dilation
better. The disadvantage is: Brown eyes look like dilated pupils anyway
and brown eyed people look on the average friendlier but with less
variability of emotion. In other words all the metaphors about "ice
princess", "steeley eyes" etc allude to aloof individuals who have a
harder time hiding their aloofness because of their eye color.

Ken wrote
It matters not to me how many alleles are participating to various
degrees in the brown dominance. It's sort of like the issue of DYS464;
there are a number of interesting different things going on in the
mutations of this 4 copy marker. If one knows or finds the rules of the
mutations, the marker can be used for purposes of population studies,
without fully understanding the different underlying mechanisms of
change in the STR lengths, as interesting as learning the underlying
mechanisms will also be.

All I need are that the final rules of inheritance for a digitized
phenotype dichotomy (brown versus non-brown eyes) 1) work most of the
time, and 2) the two defined phenotypes can correctly be sorted most of
the time. Population studies can survive small enough error rates.

I will outline the problem which intrigues me but apparently no one
else, as I have tried to discuss it a number of times previously on the
list, and the subject always gets diverted to something else.

If the areas of Europe with very high frequency of blue eyes today had
been populated by just one immigration of people who had overwhelmingly
converted to blue in the early days of the group's existence, I could
consider that an accident and perhaps a sufficient explanation for what
is seen today. But these areas of Europe are believed to have had major
and separate immigrations of several male haplogroup populations ---
R1b, I1a, R1a, N3 ..... Did all four of these population movements
bring predominately non-brown genes into the area? I think this gets
too improbable. So selection had to sweep almost all the brown genes
out of the populations in a rather short time, given the dominance of
brown genes, yet we see very low frequency of brown eyes over vast
sweeps of Europe (from Ireland to Russia) populated by multiple flows of
immigrants. I am sceptical of such rapid selection, but maybe in the
end that will have to be the explanation of what is seen. Some of the
mixings of these populations in Europe are only several thousand years old.

Someone did send me some maps like you mentioned concerning Norway and
surrounding areas. I don't know if they were from Coons' book? I can't
read the Norwegian too well, but I think they combine eye and hair
coloring as a single variable which makes things a bit messy; there are
populations of dark hair but non-brown eyes in parts of Europe.

But the maps of Norway do show some regional clines which tantalizingly
seem to correlate with some apparent regional differences in R1b, I1a,
R1a breakdowns of the Norwegian regional populations. What I think is
needed for starters is a good census by region in Europe of the
frequency of brown eyes --- to then be cross-correlated with the
frequencies of the different yhaplogroups in the regions. I'd suggest a
similar examination of the mtdna frequencies, but I have the impression
the clines and pockets of frequency variations are not as strong in the
mtdna as there are in the ydna?

The first time I had a glimpse of this issue I asked myself, "what was
the frequency of brown eyes among the I1a when they started to go north
after the last glacial maximum --- given that I1a are predominately
non-brown eyed today?" And of course the issue got broadened rather
quickly after looking around Europe.

Ken

This thread: