On 07/07/2006, at 2:20 AM, David Hobby wrote:
But it's genetic drift that CAUSES the inbreeding, isn't
it? (It's not the fall that kills, but the impact. : ) )
No. Inbreeding is a description of closed populations, such that
deleterious recessive alleles may become more frequent, and so
population fitness reduces (also the population tends to become
genetically homogeneous, also a bad thing...). Genetic drift is a
measure of the shifting mean of a trait, roughly.
I grabbed some information from a randomly chosen page:
http://www.ucl.ac.uk/~ucbhdjm/courses/b242/InbrDrift/InbrDrift.html
It states that the effective rate of inbreeding due to
drift increases roughly as 1/2N per generation, where N
is the population size. So it would take a population of
500 around 1000*ln(2), or 700 generations to double the
effective rate of inbreeding. I presume that would be
a tolerable amount?
Depends on what recessives they're carrying...
Increased genetic drift = faster evolution. Inbreeding = risk of
dying out. Some outbreeding balances these out (lowering the rate of
drift, but also decreasing frequencies of deleterious alleles).
Yes, I agree, the point is hardly changed. But then why the
big argument when I pointed out in the first place that it
probably wasn't ALL humanity that was descended from one
individual in the recent past? (I blame the authors, who
claimed "all" without having too much basis for it. Wouldn't
"almost all" have grabbed headlines as well?)
That's probably what they actually said, newsy science write-ups tend
to be hyperbolic and inaccurate. :-)
...
Their are other candidate groups. Google "uncontacted peoples".
You seem to have trouble grasping the timescales here. It's a very
common problem when talking evolution.
Charlie
Charlie-- That last bit is insulting. (Pouts.)
Don't read it as such, it wasn't meant to be. It's just an
observation based on what you've said thus far. :)
It's pretty hard
to know exactly how much contact there was between different groups
unless the groups kept records. One could argue that there was no
new influx of genes to the Americas between 10000 BPE and 1492.
One certainly could.
This takes a bunch of assumptions, that the land bridge was closed
and that the Norse (etc) contributed no genes.
I suspect a lot more travel via the Aleutians than is historically
recognised.
If so, one who wanted
to prove that everybody was descended from a Eurasian of 5000 years
ago would have to show that all of the native peoples of the Americas
had picked up some European blood in 20 to 25 generations. Even
tribes deep in the Amazon jungle...
Again, it doesn't take much outbreeding at all. But yes, you're
largely correct.
It could be true, or not. I doubt we'll ever know.
Not 'til the full mitochondrial dna cladistic tree is created.
Charlie
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