New Scientist : Many human genes evolved recently ( As recent as 15,000 years ago )

New Scientist ^ | 03/07/2006 | Melissa Lee Phillips

[SirLinksalot]

Many human genes evolved recently

01:00 07 March 2006

NewScientist.com news service

Melissa Lee Phillips

Human genes involved in metabolism, skin pigmentation, brain function and reproduction have evolved in response to recent environmental changes, according to a new study of natural selection in the human genome.

Researchers at the University of Chicago, US, developed a statistical test to find genomic regions that evolution has favoured over the last 15,000 years or so – when modern humans dealt with the end of the last ice age, the beginning of agriculture, and increased population densities.

Many of the 700 genes the researchers identified – especially those involved in smelling, fertility, and reproduction – are also suspected of having undergone natural selection during the divergence of humans and chimpanzees millions of years ago.

But some of the newly identified genes fall into categories not previously known to be targets of selection in the human lineage, such as those involved in metabolism of carbohydrates and fatty acids.

Milk lovers “It’s reasonable to suspect that a lot of these are adaptations in response to new diets and agriculture,” says team member Jonathan Pritchard.

For example, gene variants that improve the digestion of lactose have become more common, presumably since the domestication of cattle provided a ready source of milk. And in some Europeans, genes giving a lighter skin have increased in frequency, as populations have moved north to regions where there is less sunlight to generate vitamin D.

The researchers analysed the genomes of 209 people from Nigeria, East Asia, and Europe. They found widespread signals of recent selection in all three populations.

Only one-fifth of the 700 genetic regions identified were shared between at least two of the groups – the rest were unique to single populations. That supports the idea that the adaptations are recent, Pritchard explains.

Huge list The statistical test is a “powerful way of looking for selection in the genome”, says Michael Hammer of the University of Arizona in Tuscon, US. It looks for certain patterns of DNA – called linkage disequilibrium – that show a gene variant is young. It then identifies those that appear at high frequencies, which suggest they have been selected for.

Definitive proof that the gene variants are being favoured in the human genome will require detailed analysis of the changes they cause in proteins and how this affects fitness. But Hammer says “they’ve given us a huge list of candidates".

Nonetheless, there are likely to be many more, says Peter Andolfatto of the University of California, San Diego, US: “The genes being mapped here at best probably account for only a small fraction of the targets of recent selection in the human genome.”

Identifying the gene variants that are under selection may one day help medicine, Pritchard adds. That is because individuals with a newly evolved gene variant may be better adapted for modern human conditions and less susceptible to certain diseases. Understanding the differences could help guide future therapies.

Journal reference: Public Library of Science Biology (vol 4, p e72)

[Alter Kaker]

But evolution MUST start with a random, non-directed mutation in an individual, won't you agree? And then that individual's progeny must out-compete the other individuals, right?

Individuals don't have to compete, but genes do. New genes can and do spread rapidly through populations.

[lepton]

Interestingly, while the Scandinavians are fair complexioned, the Eskimos are dark skinned.

Do they get their vitamin D from sunlight, or from food? Clearly they don't leave enough exposed skin for its color to matter so much.

[Redcitizen]

My blue jeans devolved into faded jeans...

[Elpasser]

But the mechanism MUST be through one's progeny. You make it sound like genes spread like lice.

[Elpasser]

But the Laplanders DO leave enough exposed skin to matter?

Take your finger and trace around the globe from Northern Scandinavia to Alaska. Same altitude; both a somewhat milder climate on the coasts; bitterly cold in the interior.

Let's all be more skeptical about news items like this. After all, the scientists quoted in the article "suspect" or "have reason to suspect."

[Alter Kaker]

But, consider, 6,000 years and no evolutionary change toward fair complexion?

How do you know what eskimos looked like 6000 years ago?

How, then, can we confidently deduce that light-complexioned scandinavians "evolved" in 10,000 or 15,000 years?

You tell by counting certain kinds of mutations in the genes responsible. Mutations are random but occur at a predictable rate, and by tally the number of discrepancies in two individuals' copy of the gene you can determine its age.

[jwalsh07]

"For example, gene variants that improve the digestion of lactose have become more common, presumably since the domestication of cattle provided a ready source of milk."

Human milk contains, on average, a higher percentage of lactose than does cow milk.

That being said, the ability of adults to digest lactose seems to be directly correlated to whether those adults descend from areas where cattle were domesticated.

So in essence, what we have here is human directed adaptation. Interesting mechanism.

[Elpasser]

But you are assuming that the eskimo is a descendant from a particular prototype with "non-mutated" characteristics, are you not? How do you really KNOW (as opposed to speculating)?

And how do you know that the same modern gene wasn't in the gene pool 15,000 years ago?

[ToryHeartland]

And then that individual's progeny must out-compete the other individuals, right?

Not in one simple step! I think you need to go back to basics on this ... how long have you got?

[Elpasser]

"How do you know what eskimos looked like 6000 years ago?"

Don't be silly.

[Alter Kaker]

But the mechanism MUST be through one's progeny. You make it sound like genes spread like lice.

Yes, but genes spread extremely rapidly through progeny -- they spread faster than lice. Just do the math. If you have two children and your children each have two children, etc., in 35 generations (about 2000 years: a blink of an evolutionary eye) 34 billion people will be descended from you. That's more individuals than have ever lived since the dawn of the human race.

Obviously those numbers are inflated because there will be considerable overlap when your descendents marry one another, but even so you can clearly see how a succesful mutation can quickly spread rapidly throughout a population.

[blam]

"How, then, can we confidently deduce that light-complexioned scandinavians "evolved" in 10,000 or 15,000 years? Where's the evolutionary advantage in that if Eskimos aren't visibly evolving in the same basic climate? "

There's a pretty simple answer. The Eskimos have a diet of seafood and animals that eat seafood. Seafood is very high in vitamin D and the Eskimo's didn't have to 'lighten-up' to get sufficient amounts of Vitamin D.

Now, the Scandinavian ancestors probably came from Northern China in the Gansu region and on the Euro-Asian steppes. (also, Northern Pakistan)

The Northern Chinese are descended from SE Asians who have darker skin and Sundadont teeth. The Northern Chinese have flatter faces, lighter skin, peculiar eyelid and have sinodont teeth (shovel).

BTW, Kennewick Man had Sundadont teeth.

[Deathmonger]

Eskimos get their vitamin D from their extreme seafood diet, which may explain why they didn't need to lighten up like northern European peoples living inland on more conventional diets.

http://www.discover.com/issues/oct-04/features/inuit-paradox/

[Alter Kaker]

But you are assuming that the eskimo is a descendant from a particular prototype with "non-mutated" characteristics, are you not?

I'm not sure I understand your question. You can date the emergence of any gene by tallying mutations. If the gene predates extant "eskimo" populations, the tally will indicate that.

[Alter Kaker]

Don't be silly.

How is that silly? You're making an affirmative statement that eskimo morphologies today are identical to what they were 6000 years ago, and I'd like to know what basis you have for making that claim.

[keithtoo]

The Eskimos live in an environment that is snow-covered for more of the year than Scandinavians. You can get very sunburned in a snow-covered environment. Plus Eskimos are really Asians in a cold climate. They started out darker.

[blam]

"Interesting. But would the ice age also affect African populations? And if so, as much as in Europe?"

There are a few places that would have been ideal places for humans to thrive during the Ice Age. Those are Africa, parts of South America and SE Asia, Europe was pretty much covered by a huge ice slab and the areas that weren't, were very cold, Neanderthal territory more-or-less. Everyone outside Africa (alive today) are more closely related to themselves (Asian, Polynesians, SE Asians, European and etc.) than they are to Africans. The line from Africa that produced everyone outside Africa no longer exists in Africa, it went extinct some time after the 'Out-Of-Africa' folks left.

It is my opinion that the people we call Mongoloid and Caucasian today were defined from a common root (maybe the Jomon) sometime during the Last Glacial Maximum(LGM), 18-23,000 years ago. The oldest (undisputed) Mongoloid skeleton ever found is only 10k years old (oppenheimer), a fairly new body style. The Ainu of Japan (and Kennewick Man) are descendents of the Jomon too.

I think most of the people alive today (outside Africa) can trace their roots to Sundaland. (Maybe Atlantis?)

The oldest DNA on earth is contained in a small tribe in Malaysia, the Oorang Asli people, not Africa. The oldest bronze smelting site ever discovered is in Thailand, not the Middle East.

I think we have some big suprises yet in South America.

[blam]

"Turns out your body DOES know how to digest stuff like that. But trans fats, and hydrogenated vegetable oils, that they've been telling us for years and years and years is "Good for ya" are only about four hydrogen atoms away from being legally and chemically classified as PLASTICS."

I swear, I've had similar sentiments. (I'm getting to be an old geezer too, lol)

[djf]

It must be just a coincidence that the skyrocketing amount of cardiac problems, obesity, and diabetes came along at the same time folks were brainwashed to not eat pork bellies and chicken ova, and eat tofu and bran muffins instead.

Yeah, for sure, it's a coincidence.

[Pharmboy]

Excellent information. I think I speak for all Freepers who are familiar with your posts by thanking you for 1) clearly labeling appropriate sections as "your opinion" when it is; 2) your objectivity and 3) documenting your facts.

Great job.