TV Show QI. re dogs

[##Wardy##]

Just saw an episode of QI where Stephen Fry stated dogs are unique insofar as they have by far the most different breeds of ONE species.

I am a little confused. Surely fish are a species and there are thousands of breeds of them as opposed to say 300 odd breeds of dog.

Without myself doing a confusing search can anybody explain what Fry was going on about. I am all confused. Perhaps I misheard.

[lizwiz]

there are over 24,600 different species of fish.
there is one species of dog.

basically, fish aren't breeds, the different types are species.

[##Wardy##]

So what is the difference between a breed and a species?

A Yorkshire Terrier is as different to a St Bernard than a guppy is to a shark, surely?

[fairkatrina]

Basically, different breeds can produce offspring, whereas different species cannot. No matter how similar a guppy and a shark seem, they could never mate successfully, whereas a yorkie and st bernard could.
A species is usually defined by its ability to reproduce, therefore no matter how close genetically we are to gorillas (for example) one could not impregnate you, making it a seperate species.
A notable execption are horses and donkeys, which are sepreate species but still able to reproduce. Their offspring (mules or gennets depending on gender) are always infertile, thus preventing them from being a species in their own right.

[Noweia]

Dogs are also unique in being the species with the most variation i.e. body size, color, temperament. Other animals that have been domesticated as long as the dog don't have this variation and nobody yet knows why this is.

[##Wardy##]

thank you for all your answers.