Re: Adaptive landscapes and drift Was Re: Ears under pressure.

Bill Burnett (
Tue, 31 Oct 1995 10:23:47

I wrote...

>>Quite so. In fact the whole concept of an adaptive landscape works much
>>better when you include genetic drift, and Wright's 'Shifting Balance'
>>hypothesis is heavily dependent upon it.

and Thomas Clarke writes:

>But genetic drift can only produce significant change when the
>landscape is flat in the relevant dimensions subject to drift.

Not strictly true. In large stable populations yes, but drift should be
inoperative in an effectively infinite population anyway. In Wright's
conception of the adaptive landscape is disturbed by population fluctuations.
A population crash or bottleneck following e.g. a catastrophic or colonisation
event can result in very rapid drift and the formation of new allelic
combinations which might be disadvantageous compared to the original status
quo but which may allow the recovering population to scale a new (different)
adaptive peak... which may or may not be 'higher' than the starting one.
For a better explanation I can only point you back to Hartl and Clark (1988)
again. The point is that drift provides a very convincing mechanism for
change in fluctuating populations in combination with selection... The whole
vitriolic selectionist/neutralist argument was/is in my opinion (and from my
perspective) a complete waste of time.

I'm not going to try and relate this to the AAT thread, but I believe your
assertion that drift only works in a 'flat' adaptive landscape to be incorrect.

>You are going to have to work very hard to convince, me or I suspect
>most people, that bipedalism arose entirely through genetic drift.

No of course it didn't, that would be silly.