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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.

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