On 11/01/2011 02:03 PM, Warp wrote:

>    Actually the definition of "species" is a hard one.

Yes, actually.

I suppose back when everybody thought that all life was fixed and 
unvarying forever, it seemed less problematic. But now that we know that 
one species gradually changes into another... it's a bit like trying to 
classify whether a specific colour is "red" or "orange". The distinction 
is almost arbitrary.

>    By definition two animals are of different species if they cannot produce
> fertile offspring. However, this definition is lacking.
>
>    It's lacking because the definition implies transitivity:

There's a much bigger problem: Some species reproduce asexually. (!)

> However, there are eg. so-called ring species (look it up)

Another of the interesting items from The Ancestor's Tale which my 
initial post skipped over. A continuum of organisms, distinct at the 
ends, but continuous and unbroken across the middle.

>    A ring species is actually an excellent demonstration of how speciation
> can happen gradually, unlike the straw man that some creationists present
> of "a species suddenly transforming into another".

It also neatly demonstrates that geographic separation is not a 
necessary condition for speciation.

>    The difficulty of classifying B in the example also demonstrates the
> completely fuzzy line between when a species becomes another species.
> If you trace the ancestry of a modern species back to an ancestral species
> which spawned one or more other modern species, it's hard to define when
> exactly the modern species became to exist exactly.

Ring species show fuzziness in the spatial domain, ancestor trees show 
it in the temporal domain. Either way, the problem remains the same: how 
to map discrete names to continuous phenomena?

Post a reply to this message