Larry Moran wrote:
> On Tue, 2 Mar 2004 04:48:40 +0000 (UTC), 
> Jeffrey Turner  wrote:
> 

> 
> But that's not what I had in mind. I was referring to the fact that Asian
> elephants have much smaller ears than African elephants. If ear size is 
> under strong selection then one has to account for this fact. On the other
> hand, if ear size is non-adaptive then the difference between Asian and
> African elephants could be due entirely to chance.
> 
Of course, African and indian elephants live in different environments, 
with different selection pressures, so they may have different optimum 
ear sizes.

Pan-adaptionist?  Me?

I think the explanation for large ears is that they are used for 
cooling, in which case one could examine the effect of size on cooling, 
and the necessity for cooling in the two environments, and see if the 
elephants in India need less cooling.  Then if you can show that there 
is selection pressure against large ears (e.g. because they are 
expensive to make, or they fray very easily), you might have an 
explanation that would convince Larry.  Without this sort of work, both 
points of view can be supported, and indeed both should be supported, 
until we have enough evidence to decide one way or the other.

> 
>>>Don't you see how
>>>difficult it is to make general rules? Your decision about what the
>>>"default" hypothesis should be depends to a great
extent on your
>>>original biases. This is exactly the point that Lewontin and Gould
>>>made in their original paper. If you tend to emphasize natural
>>>selection in your thinking about evolution then you will look to 
>>>adaptive explanations ahead of non-adaptive explanations.
>>
>>Considering genetic diversity, itself, gives a species an advantage,
>>you're going to have to explain why traits would develop for
>>non-adaptive reasons.
> 
> 
> Two points ...
> 
> 1. Genetic diversity cannot be an adaptation since this requires a form
>    of group selection that has been thoroughly discredited. If a species
>    accidently possesses more diversity then it will be the lucky survivor
>    when the environment changes. This is more like evolution by chance
>    that real adaptation.
> 
Two points ...
1. Inbreeding depression is a form of lack of genetic diversity that can 
increase the chance that a population goe extinct.  This will generally 
work at low effective population sizes.

2. If you view diversity as a trait of a group, and has sufficiently 
high "heritability" (i.e. heritability at the group level), then it can 
evolve.  For example, if the environment keeps on changing.  To be 
honest, I doubt this is a major force in evolution, but it might work in 
some cases, for example with species competing against each other.  This 
is an example of the sort of group selection that hasn't been 
discredited (yet) - trait group selection.

Bob

-- 
Bob O'Hara

Dept. of Mathematics and Statistics
P.O. Box 4 (Yliopistonkatu 5)
FIN-00014 University of Helsinki
Finland
Telephone: +358-9-191 23743
Mobile: +358 50 599 0540
Fax:  +358-9-191 22 779
WWW:  http://www.RNI.Helsinki.FI/~boh/
Journal of Negative Results - EEB: http://www.jnr-eeb.org
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