A surprisingly recent instance of human evolution has been detected among the peoples of East Africa. It is the ability to digest milk in adulthood, conferred by genetic changes that occurred as recently as 3,000 years ago, a team of geneticists has found.

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`Irony` actually does mean `metal like`...

So at what point do we reach sufficient genetic drift to consider different human branches to be differentiated species?

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The last time I felt a warm fuzzy feeling, I was informed by my doctor that it was just gas.

Generally, when they can no longer interbreed. There's some wiggle room there where some members could still interbreed on occasion, but generally the mix results in non-viable offspring.

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`Irony` actually does mean `metal like`...

Since I'm a lactose-tolerant adult, I guess I'm a mutant. I love milk, but it is a pretty pathetic superpower.

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009
All moderation in purple

Interesting. There are exceptions to this, though. Wolves, coyotes, dogs, and a few other canines can cross the species boundary with reproductively viable offspring. The problem is the chromosome count in the offspring, not so much the genetic make up. Dogs were derived from wolves only in recent evolutionary history, so there is still plenty of genetic commonality left. So while categorically they might be distinct, their is enough genetic similarity to allow crossover.

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The last time I felt a warm fuzzy feeling, I was informed by my doctor that it was just gas.

Hum,
dogs are a bit of an evolutionary freak (ie, with their all their varieties).
It is perhaps better to say that the dogs were descended (say 9 million years ago ) from dog-bears...

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`Irony` actually does mean `metal like`...

No moreso than humans. Really. The various ethnic groups of humans are no less than groups of humans who were isolated into pockets that developed different sets of traits due to environmental and cultural desires. Blonde hair and blue eyes is one I've read was a specific development in the northernmost populations exposed to higher UV levels.

In dogs, you see wild variations because of direct human influence. We've had far greater control over which animals breed with which, and we've gone out of our way to breed true certain recessive traits that nature might otherwise filter out.

If you forced several generations of dwarfism afflicted humans to interbreed only with others afflicted with dwarfism, you'd eventually arrive at a stable population of dwarf humans that would breed almost 100% true.

Same with genetic deafness. Interbreed for that specific trait, and eventually you have an isolated pocket of purely deaf humans.

Ethnic groups are nothing more than a specific batch of features that have bred true in a given population of humans subject to local factors of culture and environment that started from the original template. Some might think that racism, but the reality is that its not. Its racist to believe any one group is superior to the other, which ultimately is untrue.

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The last time I felt a warm fuzzy feeling, I was informed by my doctor that it was just gas.

Dogs, wolves, dingos, jakals and coyotes are all the same species.

Wiki defines species as:

"A species is a reproductively isolated population that shares a common gene pool and a common niche"

Thus it is not as important that individual dogs and wolves and coyotes CAN interbreed, but whether they actually DO in their natural state. And they don't, so they are separate species.

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The Heavens Declare the Glory of Mathematics

I'm satisfied that dogs, wolves and dingoes, etc. are all the same species. Their ranges have to overlap without any natural breeding producing fertile offspring for them to be considered possibly different species, otherwise Inuit and the San of the Kalahari could be considered seperate species as they never interbreed (as far as I know). Since dogs have interbred with wolves, coyotes, etc. without human intervention they should all be members of the same species.

Geographic or ecological separation is just as good of a separator between species as biological infertility. The key phrase is "reproductive isolation", regardless of what the reason is for why the groups are reproductively isolated. That standard isn't always applied in all cases because speciation and determination of species identities isn't as simple as it's often thought of as being, but it's at least well accepted.

By the standard of geographic isolation, you could say that humanity was split into several separate species and then merged back into one due to technology.

But what brought this question up in the first place? The original post and the article it linked to were about one rather minor trait (and it's even a matter of degree rather than an absolute) which doesn't even make them different from the rest of us anyway.

Hum,
<off topic>
strangely, the people at Cornell University are just going to publish some ground breaking research on hybrid incompatibilities, which makes sense of what makes separate species...

Seemingly it requires two genes to mutate so that they become mutually destructive...(the Dobzhansky-Muller model).
</on topic>

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`Irony` actually does mean `metal like`...

Since we are getting off the meat (or milk) of the topic... two thoughts.

I add my vote to the "reproductive isolation" definition of species, whether the isolation is geographic or something else. But I also think that the whole concept of species is much less black and white than it was 50 years ago, that is, the boundaries between different species are not so sharp.

Second, I saw some TV program about dogs recently. They talked about various theories of how dogs evolved from wolves and how all the different dog breeds came about. One thing they pointed out was that a lot of the differences among dog species are not the genes themselves, but differences in gene expression, which can change a lot faster from generation to generation.

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009
All moderation in purple

Remember that the definition of "specie" is a matter of human/word definition. While it is easy to differentiate elephants from zebras, the differences between more closely related animals becomes more difficult to define. Some biologists are "lumpers" and some are "splitters". Nature does not care what we call species and many animal populations actually present a continuum from one recognized specie to sub-species, to another species. Some examples include so-called "ring species" where populations of related animals are considered separate species but are connected by related sub-species.

Taxonomically, Dogs, wolves, dingos, jackals, and coyotes are all considered different species - but they are closely related and can interbreed. The ability to interbreed is not the only or most important criteria for defining species. It is only one simple criterion that can be used to positively separate species - but the ability to interbreed does not mean that the two populations are defined as the same specie. Additional factors are used to make the determination.

Humans are all very closely related - even the most isolated ethnic groups are thought to have had signifcant gene flow between populations or to have been isolated for a relatively short (biologically) time.

Me lumper.

For the OP, that article seems to be saying they've identified at least 3 separate mutations that lead to lactose tolerance. What is not said is that it is conceivable that separate mutation events could cause the same mutation. Of course, that is probably not highly probable, depending upon what contributes to the occurrence of mutations in the first place. Either way, it would be difficult to distinguish separate mutation events that led to the exact same mutation after the fact. Thus it is easier to pick out separate events by separate mutations.

I don't know what this has to do with separating human populations into different species. "Human" is a collection of gene sequences that include many variations and mutually exclusive configurations.

According to the article, these were distinct, separate, mutations - but they all led to the same general phenotype - increased lactase expression in the adult.

Single gene mutations typically have very little to do with speciation (a much larger complex of genetic differences are normally required for species differentiation) - but they do demonstrate evolution and natural selection at work in humans in relatively recent times.

I remember reading about how powedered milk was sent to a lactose intolerant population as aid. Apparently not knowing what it was, some people used it as a laxative and it was even used as whitewash.

I keep reading that there has never been any significant reproductive isolation between human populations, anywhere.

And we are less dissimilar from each other than dogs.

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"A witty saying proves nothing" Voltaire.
"All your bias are belong to us" Ara Pacis.

I don't think there is a great deal of utility in saying that humans were several different species simply because they were isolated. Are people in the international space station a different species becauses they are seperated from the rest of humanity? If not, why not? How much seperation do you need and for how long for humans to be counted as a another species? One generation, a hundred? How could decisions on this be anything but arbitary? I think a definition of species that involves no exchange of genetic material when there is opportunity for it to occur is more useful. This seems simpler to me. Exchange of genes is common amoung humans that are not geographically seperated, even where there are large cultural differences. For example in North America, Africian and Europeans started interbreeding, both willingly and unwillingly, almost immediantly after both groups were present and the Amish contribute genes to the rest of America as many members leave and reproduce with outsiders.

Maybe not utility, but logical consistency and accuracy; the same rule has been in effect in other cases (such as the North American grizzly bear and Asian brown bear), and how much we like or dislike the outcome shouldn't make our application of scientific rules arbitrary. Fortunately, this one already was anyway , since there've been other cases where the geographic-isolation rule has not been in effect.

Time: the two populations would have to independently sustain themselves for generations. How many generations doesn't matter, because astronauts' space times don't even come close and there's been no reproducing population up there.

Arbitrariness is a long tradition in the attempts to determine which animal and plant populations are separate species and which are the same. It's generally been a matter of which answer occurs to the first biologist to describe them.

The problem with that is how it treats situations in which interbreeding is not completely impossible but is pretty close, so it's observed only rarely or even not at all for a long time. Populations that are practically entirely separate could be fused into one species by a single highly abnormal case.

That was exactly what I said early in the life of the show "Andromeda" while arguing that humans and Nietzscheans (which were derived from humans by extreme genetic and nanotechnological engineering) in that show must be two species that can't reproduce together, since it had been 3000 years and they still hadn't merged or produced any significant number of mixed individuals. (And the people I was arguing against included writers for the show! )

I'm arguing for pushing the definition in this direction because to me that would make it more logically consistant. When I am put in charge of the definition of the word species I will slowly nudge it in this direction.

Are mules a species?

They cant reproduce.

If mules could viably breed with each other horses and donkeys, would they be classed as a seperate species?

While isolated humans show different allelle expressions, they can interbreed with the general populace. My understaning is that for a new species to form, a mutation would have to occur that would not allow for interbreeding.

Would this mutation have to occur on an X or Y chromosome?

I think I'm getting confused between chromosomes and genes.

Mules aren't a species, a mule is a hybrid of a donkey and a horse. Nearly all of them are sterile. A liger is also a hybrid of a lion and a tiger. Those things are huge...

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"4th Law of Modern Thermodynamics: Where Mihoshi is, Chaos Reigns." ~W. Hakubi
"Gun control is hitting your target; Recycling is reloading your brass." ~ Lex of Dirty Work.

Yeah, I was reading the Wiki page on Ligers. Apparently they inherit the genetic growth attributes of the lion father without the counter regulating gene from the lion mother to shut it off, so they just keep growing, and growing....

Scary, neh?

From what I understand, its the males that typically end up sterile, the females can reproduce with one species or another.

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The last time I felt a warm fuzzy feeling, I was informed by my doctor that it was just gas.

I watched a show on Discovery called Humanzee, where this British scientist was going over the case of this odd chimp named Oliver, who appeared and walked much like a human instead of a chimp. It was hypothesized that he was actually the result of an experiment in seeing if humans and chimpanzees could produce any type of offspring. To help support this arguement, they showed some similiar hybrids, namely the mule and the liger. And yes, the regulator gene for growth is shut off, so they can grow to epic proportions. The one that was on the show, when on all fours, was easily up to the keeper's waist, and I think he was tall, too. You could ride on the thing like a horse, it was that big. I'd hate to see one ticked off.

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"4th Law of Modern Thermodynamics: Where Mihoshi is, Chaos Reigns." ~W. Hakubi
"Gun control is hitting your target; Recycling is reloading your brass." ~ Lex of Dirty Work.

I saw a program on Oliver. He's a chimpanzee. They sequenced his DNA and proved it. For some reason when he was young he was taught and seemed to be adept at walking upright more similar in stride to human than chimpanzee. He also typically had his head shaved to make him look more different from chimps. It seems to have been someone's scam. Nowadays he's old and knucklewalks like regular chimps.

Technically, a mule is a hybrid between a male donkey and female horse, while a hinny is a hybrid between a female donkey and male horse. They have some anatomical differences.

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

Same with tiger and lion crosses. A liger is a male lion and female tiger, a tigon is a female lion with a male tiger. Again, the offspring differ in traits.

Also note this:

This website from the University of Pennsylvania School of Veterinary Medicine, has a picture of a liger next to some people. BIG KITTY!

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At night the stars put on a show for free (Carole King)

One Earth, One Sky - IYA 2009
All moderation in purple