I’m sure this has been answered already, but I cann’t find it. But anyway I found a couple of threads, but they didn’t answer my question well.
Cats are all different species, even though there are minor differences between all the cats. A russian blue isn’t that different from a siamese cat, so why do we say that they are different species/breeds, when we will not say that humans are different species/breeds. There must be enough differnce between an aboriginie or an chinese person or a person from northern Europe to warrent making them different species/breeds or at least a different subspecies.
I asked my bio teacher about this, and he gave me a run around that didn’t make sense (well it did, species cann’t produce fertile young with other species, but that doesn’t explain why cats have different breeds/whatever).
Is there a real reason why we don’t have different species/subspecies/breeds for humans.
If you know of a thread that answers all these questions, by all means post a link. If I still have Q’s I’ll ask them here.
I personally think that the reason there are no human species/breeds/subspecies is because it is not PC to compair different breeds/species/whatever of human.
You can’t use “species” and “breed” interchangeably. They are not at all the same thing.
All domestic cats are one species just as all humans are one species. Cats have a wide range of variation just as humans do. However, the range of variation in cats is wider than that of humans because cats have been subject to a process of deliberate artificial selection (also known as breeding, hence the name), something that we do not allow for humans.
And to further confuse matters, depending on context, “cat” can mean all species in the genus felus, which includes your friendly domesticated cat as well as lions, tigers (but not bears) cheetahs, and so forth. Or its meaning can be restricted to domesticated cats, which are all indeed the same species.
Well, as for “breeds”, we certainly recognize the Japanese, Chinese, Irish, Inuit, Mediterranean, Arabic, and African sub-sets (among MANY others!). I would say that the traits of these sub-sets mark them as distinctly as the difference between a yellow labrador, a golden retriever, and a cocker spaniel (for example). Our coat colors aren’t as distinctive, but between hair-eye-skin combinations (color and texture) you can find regional variations that I would call “breeds”.
We don’t have very many absurd breeds (think of a human equivalent of a Dachshund or Great Dane) because humans haven’t been selectively bred for size. Although I’ve heard Samoans are generally large of girth.
Also, cats become sexually mature incredibly fast, have a relatively short gestation period, and give birth to multiple kittens as a matter of course whereas humans take thirteen years to develop sexually, give birth at nine months, usually have only one child at a time.
Because of those differences, among many others, it’d be next to impossible to *force * a breed of humans like we have with cats, dogs, and other domesticated animals although throughout history, natural barriers such as oceans, mountains, deserts, etc. have cut off one section of the human population from another and basically did it naturally. Aboriginees, Native Americans, Polynesians, Khoisans, Inuit, and other races are all good examples.
Certainly there are groups of humans with distinctive appearances. However, these are not at all similar to breeds amongst domesticated animals. The distinctive features of various groups of humans are not particularly distinctive. Variation within these groups is wide, and overlap with surrounding groups is great. Moreover, we’re all interbred to hell and gone. There are no human groups that have been genetically isolated from surrounding populations for any significant period of time.
On the other hand, breeds, where we’re talking about purebreds (and crosses and mongrels very rapidly lose breed-distinctiveness) are both genetically isolated to a tremendous degree, and are required to conform to very, very specific standards of appearance. For example, from the AKC’s website, an excerpt from the breed standard for the Cocker Spaniel:
Now try to imagine a “breed standard” for any group of humans. The very idea is preposterous, and not for reasons of political correctness, but simply because even within very homogeneous groups there is far too much diversity.
IIRC the definition of species is to the effect that 2 animals of the same species can breed, whereas 2 animals of different species cannot. This is probably what your bio teacher was trying to say.
Breeds have well defined characteristics or lineages. I’d like to see you come up with some clear definitions for human races and the ability to unambiguously identify which race a particular human belongs to.
Human beings have relatively little genetic variation within the species compared to other species. This is because we went through a population bottle neck about 100,000 years ago. This isn’t enough time for evolution to take one species and split it into multiple species, or even provide much variation within one. Also, Humans are a wandering species and there would in most cases be enough interbreeding to keep the species relativly homogenous.
There is far less variation between any two humans than there is between you average pair of dog breeds. Of course, as human beings, we are very sensitve to these minute differences within our species; we spend most of our time dealing with fellow humans.
It really depends on your definition of breed. In the dictionary I have breed is defined as the following:
[ul]
[li]A group of organisms having common ancestors and certain distinguishable characteristics, especially a group within a species developed by artificial selection and maintained by controlled propagation. [/li]
[li]A kind; a sort[/li][/ul]
So using a loose definition of breed, you can class humans into groups with certain distinguishable characteristics. But if you go by any more exact definition, then you can’t really compare the two. Humans weren’t artifically selected and controlled by propagation, so using the term breed is probably best left to cats and other animals.
Even the definition of the word species is still subject to debate among scientists. There’s many definitions but each has at least a little problem that comes along with it.
That’s one definition, but not one that ever had much credibility and one that is rapidly losing favour.
Two organisms of the same species must be interfertile frequently but there is no requirement for absolute interfertility. It is very common amongst plants and microbes for organisms to have mechanisms that prevent intra-strain reproduction. What that means is that many organsims are not intefertile with their close relatives. That does not mean that they are not the same species. Even amonsgt humans there are frequently couples that are incapable of breeding due to genetic problems, That doens’t eman that these couples belong to different species.
There are numerous examples of organisms of the same species interbreeding, even in the wild. Blue and fin whales, coyotes and wolves etc. There can be little doubt that these are separte species and yet they remain completley interfertile.
As you can see this somewhat simplistic defintion alls down on all the important points.
I should also point out that a crucial aspect of breeds in domestic animal is that they breed true. Two animals of the same breed will pop out babies with all the characteristics of that breed nearly 100% of the time (not quite, actually - there are occasional throwbacks. But these are very, very rare.) Now, this only works if every animal in the breed is homozygous with respect to all the characteristics of that breed. This is only maintainable with strict breeding standards. Any breeding from outside the strain will allow heterozygotes into the breed, and next thing you know, you’ve got Polled Herefords showing up with horns, or German Shepherds with floppy ears.
With people, the way we screw around with neighbouring populations, you just don’t get groups that are 100% homozygous. Your blond, blue-eyed Vikings go on a little raiding expedition and bring back some nice brown-eyed girls from the continent, and next thing you know there are brown-eyed Vikings. Without extensive eugenics programs, you just can’t maintain “breed purity”. In short, there basic reason there aren’t any real human “breeds” can be summed up in one word. Exogamy.
You just haven’t seen the results yet because of breeding time, as Aesiron pointed out, and because the criteria for the breed is choosen by the breed itself, a more haphazard method. Also medical (plastic) and dental science is null and voiding some of the mate selection.
There are separatist groups who keep banging on about racial purity, but I suspect their methods of selection are a little too arbitrary to be comparable to pedigree animal breeding.
Then there’s Homo Regis - that subspecies of humanity known as ‘The Royal Family’ - but the great efforts that have been made there to keep the lineage pure from alien genes have not always succeeded, so I guess they’re out of the running too.
So wouldn’t certain African tribes fit this rule? Like the ones that are really tall or the pygmies? (didn’t Cecil just rerun a column on them recently?) Did pygmy mothers ever have the occasional tall child? I always assumed the populations were probably extremely isolated and had a smaller gene pool which led to the extremes. It seems like there might have been human “breeds” at in the days before relatively easy travel…
