Hi all,
Well, if us non-ornithologists are going to play ornithologist, we need to
know the real rules, don't we? :)
I would say that the distinction between species' DNA and individuals of
that species isn't a real big amount; in other words, genetics seems to me
to be not very quantitative, but more qualitative.
Anyway, good birding!
BTW, I saw an American Robin yesterday in my yard.
Richard
>From: Christian Kessler <>
>Reply-To:
>To:
>Subject: Re: [MDOSPREY] Good and bad news for birdwatchers
>Date: Wed, 21 Feb 2007 08:01:58 -0500
>
>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
>>
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