man-ape hybrid

Bill Burnett bbur at wpo.nerc.ac.uk
Tue Oct 3 09:52:25 EST 1995

In article <Pine.SUN.3.91.951002095006.22944B-100000 at chuma> karl at CHUMA.CAS.USF.EDU ("Stephen A. Karl") writes:
>Subject: Re: man-ape hybrid
>From: karl at CHUMA.CAS.USF.EDU ("Stephen A. Karl")
>Date: 2 Oct 1995 12:25:21 -0700

>4) species status can (and should?) be assigned based upon a variety of 
>   characteristics.  How about this -- is two organisms are 
>   reproductively isolated then they are two species.  If not, and there are 
>   other characteristics (ecological, behavioral, etc.) that clearly delineate
>   the organisms then they are two species.

I think it depends on what you want a species definition for...
If you want a species definition that allows you to catalogue things, then you 
can use ecological / behavioural / morphological characters and define 
whatever you like as a species.

If you want something which suggests an independent evolutionary unit (and 
leaving out asexual lineages and reticulate evolution for the time being...) 
then the presence of a barrier to genetic exchange (i.e. a 
reproductive barrier) is a prerequisite.  'Biological species' are generally 
defined as  groups of individuals which interbreed with one another but not 
with members of other such groups which occur in the same place (see various 
papers and books by Ernst Mayr for (IMO) a pretty good justification).  
Personally I find this the most useful definition to date.  

Problems arising from occasional hybridisation are unlikely to be important in 
large populations (though the situation in plants and some inverts. eg. 
Anthozoa may be more complicated) as the initial frequency of introduced 
alleles will be low and chances are they'll be lost in the first couple of 
generations (unless there's a very strong selective pressure for the new 
allele....)  Introgression is more likely in small populations, so keep an eye 
on those endangered turtle species (pity about their long generation times...).
What's my point?  I think occasional hybrids are usually unimportant (in 
animals) and a biological species concept is the one to run with...



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