Species, breeds and stuff.

[the tree]

Is there really a clear difference between species* and breeds?

 

An alsation looks a lot like a wolf, but they are seperate species. An alsation doesn't look a thing like a shi'tsu yet they are only different breeds. What's up with that?

 

*Don't know the plural.

[PhDP]

Yes,

 

http://en.wikipedia.org/wiki/Breeds

[the tree]

O.k. that really really didn't help. I still don't get how it is decided that two things are different breeds or different species.

[john5746]

O.k. that really really didn't help. I still don't get how it is decided that two things are different breeds or different species.

 

I am not an expert, but looks like a breed is a result of domestication. The two examples you gave: (1) DIFFERENCE BETWEEN A WILD ANIMAL AND A DOMESTIC ANIMAL (2) DIFFERENCE BETWEEN TWO DOMESTIC ANIMALS.

 

No wild animal can be considered a breed?

[imasmartgirl]

well i think breeds can breed and have offspring and two species cannot breed.

[the tree]

well i think breeds can breed and have offspring and two species cannot breed.

Nu-huh, a horse and a donkey manage but back to the alsation and the shi'tsu, wouldn't work.

[PhDP]

By definition, individuals from distinct species cannot breed and have fertile offsprings, but distinct races/"breed" of the same species can.

[Mokele]

Well, first, you're right, the plural of "species" is also "species".

 

Secondly, the problem with breeds and how they correspond to species is partially one of word definition. Species are technically defined as two populations that are no longer able to interbreed and produce fertile hybrids, but this definition falls down in the real world when faced with things like allopatry or clearly different species that can make fertile hybrids. I even know of cross-genera hybrids, though I don't know if they're fertile. "Breeds" is even worse, and are mostly defined by the presence of particular physical traits, with only tangential relation to ancestry, reproductive compatability, or genetics.

 

Basically "breeds" is a crappy word, from the scientific perspective. Basically, a "breed" is a population which has been exposed to very strong directional selection until certain traits are 'fixed' in that population. How long they were isolated for, overall genetic difference,and reproductive compatability can vary tremendously as a result of the breed being defined only by phenotypic traits. Black labs and chocolate labs are different breeds, defined by traits, but are so close that the evolutionary distinction is almost nil (at most, the level of 'varying populations'). Chihuahuas and Alsatians, on the other hand, have probably been separate for a long time, likely have some big genetic differences, and cannot interbreed in one way (though a male chihuahua might be able to father pups with a larger dog), and yet they are still "breeds"

 

So basically, "breeds" is an almost meaningless term for populations that have been isolated and selectively bred (and inbred) for varying lengths of time at varying intensities with varying results.

 

Mokele

[the tree]

Thanks, I was getting the feeling that breed might not be that scientific a word.