On 13-1-2011 12:45, Warp wrote:
> Invisible<voi### [at] devnull>  wrote:
>> On 12/01/2011 04:12 PM, Warp wrote:
>>> Invisible<voi### [at] devnull>   wrote:
>>>> If you can't, take a look at dogs. Some kinds can't interbreed with each
>>>> other, if only due to huge differences in size. Humans did that.
>>>
>>>     I don't think that is what defines a species. It's about genetics.
>
>> How about this: There are two species of grasshopper that never
>> interbreed. The females of species A ignore the songs of males of
>> species B. However, if you mute the male and play back a recording of a
>> male of species A, the two will mate, and produce viable offspring. It's
>> just that this only ever happens in the lab.
>
>    The definition of species is related to genetics, not to behavior.

No that is a choice and one that not everybody agrees on. It might be in 
your biology book but that does not prove much.

>> Similarly, there are probably classes of birds where you could do the
>> same thing by putting coloured visors over the bird's eyes, or moths
>> where you could mask one chemical pheromone with another. Are these
>> separate species?
>
>    It's about genetics, not about behavior.
>
>> You can apparently mate a lion with a tiger, producing either a "liger"
>> or a "tiglon". (Go look them up.) But this never happens in the wild (as
>> far as we know).

Given that their habitats do not overlap...

> Are these separate species?
>
>    The offspring must be fertile. Ligers and tigons aren't.

That too is a choice that not everybody agrees on. It is still often 
used as a definition, read the origin of species for many examples where 
this does not make sense. Among other things offspring of two 'species' 
that are more viable than the pure breeds.

No definition of species exists that is not violated in some 'species'. 
I think it may be hard to find a biologist in this field that would 
supply you with something more than: 'in most cases this will match you 
intuitive concept'. I can live with that. People whose mental health 
depend on the assumption that there is a clear definition of 'species' 
may freely ignore the evidence.

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