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From: RonO <rokimoto557@gmail.com>
Newsgroups: talk.origins
Subject: Northern elephant seal genetics
Date: Sun, 29 Sep 2024 16:49:48 -0500
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https://www.nature.com/articles/s41559-024-02533-2

This article is open access.

The Northern elephant seal was hunted to near extinction, but a small 
population survived on some out of the way island.  Likely due to most 
males not producing offspring the paper estimates that the effective 
population size was only 6 at the point of the genetic bottleneck.  This 
is about the effective population size of Noah and his family of flood 
survivors if they all managed to produce a boat load of progeny each.

Not surprisingly this population has a lot less genetic diversity than 
the Southern population that did not suffer the same near extinction 
event.  Surprisingly, individuals do not seem to be suffering from 
inbreeding depression.  It may be that the surviving breeders had less 
than the average genetic load, so the extant population has fewer 
deleterious variants.

The Northern and Southern populations are closely related and they 
likely could reintroduce genetic variation from the South, but since 
they don't seem to be suffering from inbreeding depression my take is 
that they should allow the population to continue as an independent 
population and see if it eventually takes over both the Northern and 
Southern territories.  These lucky population expansions have had to 
happen every once in a while for all species.

Large stable populations will tend to accumulate recessive lethal and 
sub lethal variants.  Eugenics failed because it was never going to 
work.  Even if you have 100% selection against the homozygotes a 
recessive lethal will not be effectively selected against once the 
allele frequency drops to around 0.03 (6% of the population are still 
carriers).  There are thousands of recessive lethals segregating in the 
human population.  In order to reduce the genetic load you need to get 
lucky with some sub population that due to founder effects/genetic drift 
do not have as many recessive lethals.  Most small sub populations 
likely fail in isolation because they were not lucky and inbreeding 
depression will wipe them out, but once in a while some sub population 
will come out cleaner than the parent population.  It could be the 
reason that we see allopatric speciation events and Gould and Eldridge's 
punctuated fossil record.  A slightly different sub species comes back 
and takes over the parental population's territory.

Ron Okimoto