More breeds of Dogs, or Horses or Humans ?

breed definition part 2: who can still mate and produce virile offspring....?

Yes.

I think you mean "fertile" offspring, not "virile", but I get your point

Mating to produce fertile offspring is a species level requirement. Breeds can interbreed without difficulty. I've always thought of breed like race in humans, but it may be more like sub-race.

I think "breed" and "race" are basically the same thing from a scientific classification point of view. They are only different in a socia-political context.

It should be noted that for all practical purposes a "breed" must breed true.

A Holstein cow and a Holstein bull will always have a Holstein calf.

A Belgian stallion and a Belgian mare will always have a Belgian foal. And in North America the foals ancestry can be traced to any one of four stallions.

If a bull or cow is not pure (considered at least 7/8th or 15/16ths) by most breed associations then the calf will not necessarily resemble either parent.

Same would hold true for people except that there is no "closed herd book" for humans. They also have a bit of a tendency to "jump the fences" so as to speak.

Occasionally a breed association will open the herd book (or its equivalent) to new bloodlines. This can be done if the environment (usually the economic one) changes so quickly that economically valuable characteristics cannot be selected for within the breed fast enough for the breed to remain economically viable.

akaMechsmith is absolutely correct. That is why it's not very meaningful to talk about race among humans. It would be very difficult to find someone who is not of mixed-'race'. Pehaps among some very isolated pre-industrial people in remote rain forests, perhaps not even there. We have an unfortunate tendency to think of 'race' in terms of skin pigmentation. Yet the Australian Aboriginals are every bit as dark-skinned as most sub-Saharan Africans but there are no DNA correspondences between these two 'racially' disparate people. (Except, of course, where there has been influx of Caucasion DNA into either peoples' makeup.)

The Jews like to claim they can trace their linage back to Juda (grandson of Abraham) about 3000 years ago, and I suppose many of them meet the 15/16 th rule. Adolf Hitler also attempted to produce pure Aryans. Perhaps some descendents are 15/16 th. I believe a small subset of the Genius Club = Mensa? are attempting the breeding of humans. It is not considered politically correct to study race = breed in humans. It is definitely in bad taste to challenge the race a person may choose to claim. Neil

I very much doubt that most Jews are 15/16ths pure. All you have to do is look at the physical characteristics of any representative group of Jews gathered in one place. They are as varied as any other group of people. This is not even to mention the Falashas, black Jews of Ethiopia. Hitler's notions of racial purity were -- and are -- uproariously absurd. Where did he think he was going to find a "pure" Aryan? The so-called "blood-lines" of all Europeans are an admixture, influenced by an influx of Asian DNA during the Mongol invasions of the early Middle Ages, Arabic and other mid-Eastern DNA from early contacts during the Punic Wars and later contacts during the Crusades. Add to that the absurdity that Hitler didn't consider Slavic Europeans Aryan, and you have a madman's pipe-dream.

I'll change the question a bit: What species alive today expresses the widest range of variation?

Dogs and Horses are greatly affected by interaction (breeding control) by humans.

Are similar levels of diversity/variation evident in wild populations?

I'd bet domesticated animals have a wider variety given the nature of natural selection. Then, when I think of an animal like the sparrow which seems to make a niche for itself nearly everywhere, I start to think otherwise.

Recent evidence indicates that there were probably lots of breeds/versions/races of humanity in the past. But only one survives now.

Many breeds of horses and dogs survive today, but they don't have our ubiquity of environmental range, and they exist in large part due to our interaction with them.