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Un-Natural Selection: Human Evolution's Next Steps

Human beings are defying nature. Or at least we’re trying to.

For billions of years, species have evolved by natural selection, the process by which genetic mutations that help an organism survive are passed on from one generation to the next and harmful ones are eliminated.

But natural selection takes time -- sometimes millions or even hundreds of millions of years. Humans have only been around for tens of thousands of years, but we are changing the world so much that genetic evolution simply can't keep up.

Millions of years ago, the natural environment was shaping us into the species we are now. Today, we create our own environments, and that has its consequences.

John Hawks, an anthropologist and geneticist at the University of Wisconsin, Madison, says we've created a lifestyle that is at odds with the one natural selection provided us with. Consider, for example, what ate when we were hunter gatherers, long before we started farming.

Millions of years ago, the natural environment was shaping us into the species we are now. Today, we create our own environments, and that has its consequences.

"We adapted to a diet that was much more balanced in terms of lean meat, in terms of high fiber vegetables.  And by de-accentuating those aspects of our former diet, we've created a new environment that humans aren't real suited to," Hawks says.

Sometimes, though, genetic adaptation can happen fairly quickly. Hawks says the classic example is a mutation in a gene that makes red blood cells. It's called the sickle-cell mutation and spread through Africa once malaria became a problem there.

“That's a highly adaptive mutation where it occurs when there's malaria around, because it's protective against malaria," says Hawks. If you inherit the mutation from just one parent, you don't get sick. You only get malaria protection. It's only when you inherit the mutation from both parents that you get sickle-cell anemia. So if you're not living in a malaria environment, the mutation is just bad.” And you don’t want that gene, Hawks says, because your offspring have a chance of having sickle-cell anemia.

Keeping Bad Mutations Around

Really bad mutations tend to disappear, because the people who have them frequently don't live long enough to pass them on. That's what natural selection is all about.

But now in some cases we choose to keep these bad mutations around. Take the gene mutation that causes phenylketonuria, or PKU. People with the disease can't break down the amino acid phenylalanine, a problem that can lead to severe cognitive damage.

"It's a devastating disease that you can completely eliminate if you pick it up early," says Matthew Hirschfeld, a pediatrician at Alaska Native Medical Center.

And it can be picked up very early -- there's a genetic test for PKU that all babies in the U.S. get at birth. The treatment includes maintaining a diet with low levels of phenylalanine.

But curing the disease does not mean eliminating the mutation. Once upon a time, children born with PKU probably would never have offspring. Now they can, and that helps keep the mutation in circulation.

Choosing Our Genes

In fact, a large part of modern medicine is in the business of overcoming bad mutations.

“We want to have cures for things, we want to make things better," says Hawks. We do this with eye sight: Nearsightedness could have been fatal for people whose ability to survive depended on spotting dinner off in the distance. Now it doesn't matter if we inherited nearsightedness -- we wear eyeglasses.

"We wear contact lenses," says Hawks."You get Lasik surgery.  We can affect eye sight in many different ways. It's not perfect, but like many instances of technological development, we tinker at it and it changes and eventually we come to a point where we like it or keep changing.

We've turned the notion of natural selection on its head. Nature isn't the only force that picks the genes that stick around -- we're doing it too. We're moving toward a time when we can routinely repair, remove or even insert genes in people.

The question is whether we can do as good a job as nature has done up until now.

This story was produced by Jane Greenhalgh.

Copyright 2014 NPR. To see more, visit http://www.npr.org/.

Transcript

ROBERT SIEGEL, host:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

Evolution depends on new genes showing up from time to time. They stick around if they help a species survive while harmful genes are eliminated. That is natural selection.

But natural selection millions or even hundreds of millions of years. Humans have only been around for tens of thousands of years, and we've changed the world so much that genetic evolution can't keep up.

In the final part of our series, The Human Edge, NPR's Joe Palca explores the role genes are playing in the future of our species.

JOE PALCA: There's nothing particularly unnatural about the H2Oasis Waterpark.

Mr. DENNIS PRENDEVILLE (President and CEO, H2Oasis Waterpark): We've got a wave pool, a lazy river, two body slides; one is enclosed and the other is an open flume right over here.

PALCA: What makes H2Oasis a bit unusual is that it's in Anchorage, Alaska. Dennis Prendeville is a co-owner.

Mr. PRENDEVILLE: I've seen it 15 below zero out here and the place is packed.

PALCA: Of course, it's a big expense to heat all this water and the cavernous hall that houses the waterpark.

Unidentified Man: It's huge. Thirty thousand a month is nasty.

PALCA: The point here is if you want to build a waterpark in Alaska or a ski slope in the Arabian Desert, you can do it. Millions of years ago, the natural environment was shaping us into the species we are now. But today, we create our own environments and that has its consequences.

John Hawks is an anthropologist and geneticist at the University of Wisconsin. He says we've created a lifestyle that is sometimes at odds with the one natural selection provided us with. For example, consider what we ate when we were hunter-gatherers before we started farming.

Professor JOHN HAWKS (Anthropology, University of Wisconsin): We adapted to a diet that was much more balanced in terms of lean meat, in terms of high fiber vegetables. And by de-accentuating those aspects of our former diet, we've created a new environment that humans aren't real well-suited to.

PALCA: Sometimes genetic adaptation can happen fairly quickly. Hawks says the classic example is a mutation in a gene that makes red blood cells. It's called the sickle cell mutation. It spread through Africa once malaria became a problem there.

Prof. HAWKS: That's a highly adaptive mutation where it occurs when there's malaria around because it's protective against malaria.

PALCA: And if you inherit the mutation from just one parent, you don't get sick; you only get the malaria protection. It's only when you inherit the mutation from both parents that you get sickle cell anemia. So if you're not living in a malaria environment, Hawks says the mutation is just bad.

Prof. HAWKS: You don't want to have it because your offspring have a chance of having sickle cell anemia. These genes that have - they sort of give with one hand and take away with the other.

PALCA: Really bad genes tend to disappear because the people who have them frequently don't live long enough to pass them on. That's what natural selection is all about. But now, in some cases, we choose to keep these bad mutations around.

(Soundbite of a crying infant)

Dr. MATTHEW HIRSCHFELD (Pediatrician, Alaska Native Medical Center): So this is a little boy who was born about 24 hours ago.

PALCA: Matthew Hirschfeld is a pediatrician at the Alaska Native Medical Center in Anchorage.

Dr. HIRSCHFELD: We're doing a newborn metabolic screen. We do two of these tests on each baby that's born here in Alaska.

Unidentified Woman: Just relax and hold still.

(Soundbite of a crying infant)

Unidentified Woman: I know it.

PALCA: The metabolic screen includes a genetic test for a mutation that causes a disease called PKU.

Dr. HIRSCHFELD: It's a devastating disease that you can completely eliminate if you pick it up early.

PALCA: Right.

Dr. HIRSCHFELD: So that's why it's such a great test.

PALCA: But eliminating the disease does not mean eliminating the mutation. Once upon a time, children born with PKU probably would never have had offspring. Now, they can if they want to, and that helps keep the mutation in circulation.

Modern medicine is in the business of overcoming bad mutations.

Prof. HAWKS: We want to have cures for things. We want to make things better.

PALCA: John Hawks says take poor eyesight, for example. Nearsightedness could have been fatal for people whose ability to survive depended on spotting dinner off in the distance. Now, it doesn't matter if we inherited nearsightedness. We wear eyeglasses.

Prof. HAWKS: We wear contact lenses. You get Lasik surgery. I mean, we can affect eyesight in many different ways. It's not perfect, but, you know, like many instances of technological development, we tinker at it and it changes. And, you know, eventually, we come to a point where we either like it or we keep changing.

PALCA: We've turned the notion of natural selection on its head. Nature isn't the only force that picks the genes that stick around; we're doing it too. We're moving toward a time when we can routinely repair, remove or even insert genes in people. The question is whether we can do as good a job as nature has done.

Joe Palca, NPR News.

SIEGEL: And we have now concluded our series on Evolution: The Human Edge. You can find the entire series at npr.org. Transcript provided by NPR, Copyright NPR.

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