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Re: Of Tarbosaurs and tabbies
Because someone's bound to pull me up on this if I don't say it :P -
'gene-flow' is of course a factor of time, because if you go back far enough
all species are connected genetically.
I don't know that anyone has ever tried to define the amount of time
involved here - it's usually just fobbed off as 'at present' but gene flow
itself only exists in time (it takes a while to make a baby). Time would
vary between taxa anyway - speciation can happen very quickly in cichlids
(circumstantial evidence suggests a matter of decades, if not less) but may
take millions of years in forams.
> A species is defined by the absence or near-absence of gene flow - it
> has been defined as the point (or hazy grade) where reticulate descent
> (between interbreeding individuals) becomes secondary to linear or branching
> descent (from one species to another). Obviously, this is one of those
> wonderful definitions which are both totally accurate and completely useless
> at the same time. The various species concepts are essentially differences
> of opinion on how to actually identify this point.
> As has been pointed out, ability to interbreed is only one factor in
> identifying species. Many 'species' _can_ interbreed, but usually _don't_
> interbreed. Two species of grebe, the Clark's and the Western, can produce
> offspring, but prefer partners of the same species. Males actually become
> more willing to accept a mate of the other species the longer they go
> without a mate of the same. Females of many cichlid fishes, also, prefer to
> mate with males of the 'right' colour pattern, but can still produce
> offspring with others. This has been quite dramatically shown after some
> species have merged in Lake Victoria since rising eutrophication has reduced
> visibility and hence the females' ability to distinguish males.