ahh, to the crux of the matter. technically speaking there is a 
distinction between having different genes (two species) & different 
alleles (varieties) of one gene (individuals of the same species). but 
when one gets deep into the mechanics of it, the boundary is always, 
speaking in formal scientific terms, arbitrary. this is true of the 
genetic approach to defining species, but it is also true of the 
taxonomic (& any other) method. we all agree that humans & chimpanzees 
are different species, tho the genetic similarity is in the very high 
90s. whether red-shafted flickers & yellow-shafted flickers are all 
Northern or merely all northern (vice the tropics) is more a matter of 
definitions made by humans. which is why Ernst Mayr defined a species as 
an isolated breeding population (regardless of what the mechanism for 
isolation might be -- geography, song, plummage, habitat, whatever). 
Alvaro Jaramillo wrote a good article on this in Birding not too long 
ago. it not that there is no such thing as a "species" in nature, its 
just that nature keeps changing what the species are, & we try to freeze 
the picture.
chris kessler

RICHARD JILL WOOD wrote:
> Hi all,
>
> As a birder (and a chemist), I find this all quite interesting. 
> However, I have to ask this question: isn't the separation of bird 
> species by differences in their DNA kind of "arbitrary"? It's all 
> decided by some group of scientists that decided that species 
> differentiation occurs when there are x% difference in the DNA of two 
> species, but this x% was decided by people and not by some test that 
> isn't subject to a person making the "differentiation limit". For 
> example, this group of scientists may have decided x is 10%, so if two 
> birds difffer in their DNA by 10%, they are different species. But who 
> is to say it's really 10%? That's the problem I have with all this, 
> it's too arbitrary.
>
> Let em also ask this: what is the % difference in the DNA of two 
> individual humans that are not "related"?
>
> Good birding,
> Richard
>
>
>>>
>>>
>>>
>> The bar codes are a good indication, though, even if you might not 
>> want to treat them as definitive. The bar code consists of 648 base 
>> pairs, many of which might vary from species to species and some of 
>> which vary even inside a single species. The variation might not 
>> change the corresponding protein at all, it might not vary the 
>> protein in a way that changes its function, or it might vary the 
>> function in ways that improve its fitness under the conditions of the 
>> habitat of varying species. The variations that don't change the 
>> protein at all are especially interesting since they are necessarily 
>> not subject to selection and so tend to occur in proportion to the 
>> amount of time since the species involved stopped interbreeding. If 
>> all organisms had exactly the same protein, the variation in base 
>> pairs would be especially useful.
>>
>> For whatever it may be worth, the web page for the organization which 
>> will store this data indicates that different species generally 
>> differ in at least 5% of the base pairs.
>>
>> The problem is using the data is an old one: how long must two 
>> populations be separated before they should be regarded as separate 
>> species? What is the criterion for separate anyway?
>>
>> What I find interesting for birdwatchers in this data that has been 
>> distinctly underemphasized is that the number of potential splits is 
>> roughly equal to the number of potential lumps. Have we reached some 
>> kind of temporary equilibrium in the number of bird species?
>>
>> -- 
>> Maurice Barnhill  [Use ReplyTo, not From]
>> [bellatlantic.net is reserved for spam only]
>> Department of Physics and Astronomy
>> University of Delaware
>> Newark, DE 19716
>
> _________________________________________________________________
> Don’t miss your chance to WIN 10 hours of private jet travel from 
> Microsoft® Office Live 
> http://clk.atdmt.com/MRT/go/mcrssaub0540002499mrt/direct/01/
>
>