quote:
"... a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature." (Mayr)
This is, indeed, a common definition of species, and it is commonly used among biologists. However, this definition has several deficiencies:
The main deficiency is that it only applies to sexually reproducing species. Species that reproduce asexually, such as most single celled organisms and some parthogenetic species of lizards, can not be distinguished by this definition (each
individual is reproductively isolated).
Also, reproductive isolation is not an either/or thing - there are varying degrees of reproductive isolation; there are examples of different looking "breeds" which nonetheless interbreed readily (like dogs), and examples of populations that interbreed occasionally but rarely, and examples of populations that never, ever interbreed in the wild but can sometimes interbreed in captivity to produce viable, fertile offspring.
Worse, there are examples of
ring species such as the herring gull and the Black-backed gull; in Britain they do not interbreed at all, they were considered different species, but as one travels across the arctic to the west, the herring gull readily interbreeds with a population of eastern North America, which interbreeds with a population of western North America, which interbreeds with a population of Siberia, which interbreeds with...the black-backed gull. So, are these one species or two?
The point is that this definition of species, which is usually pretty useful, isn't too useful in certain situations. This is off topic of your post, but I should add that it is an integral part of evolution theory that populations should gradually differentiate and change into two or more species, and so it is a
prediction that there should be examples where populations aren't quite different species, yet not quite the same species either. Creationism tries to invoke some sort of evolution like this, mostly to try to explain how so many "kinds' can fit into Noah's ark, but it is added in a rather ad hoc fashion.
quote:
but how a mutation that makes me immune to malaria (which is not heriditary) can allow the emergence of a new reproductively isolated specie.
A mutation occurs in the genome, and so by definition is inheritable.
Here is some information on this mutation.
The point is that small changes
will add up to big changes - unless there is something to prevent it. Creationists try to say this is impossible either by claiming that beneficial mutations are too rare or by saying that mutations cannot increase "information" (whatever that is) in the genome. The examples I provided show that this is simply false - there is nothing in principle that prevents small changes from eventually adding up to big changes.
And you are right - it would be so nice if we can do all the necessary experiments in the laboratory. But evolution is too long a process - we cannot simply get the kind of significant macro-evolutionary change that creationists insist upon in a short amount of time (like in a human lifetime). The best we can do is show that each of the little pieces of the theory can individually be shown to work, and then hope that it's clear that each of the pieces, together add up to macro-evolution over the long term - unless someone can show why this is not possible.
[This message has been edited by Chiroptera, 11-16-2003]
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