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A 30-Million-Year-Old Virgin's Secret To Success

Science

Listen To Segment: A Long Dry Spell

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STEVE INSKEEP, Host:

Well, if you think the lack of broadband access is a problem, let's talk about the lack of something a little more basic. NPR's science correspondent Joe Palca tells us about a creature that has gone without for 30 million years.

JOE PALCA: Before we talk about no sex, let's talk about sex. From a biological perspective, sex requires a lot of work. It would be much easier if you could reproduce on your own.

INSKEEP: You don't have to find a mate. If you find a mate, you don't have to worry about things like venereal disease. You don't have to worry about getting attacked while you're in the process of having a sex act.

PALCA: That's evolutionary biologist John Logsdon, of the University of Iowa. In addition to avoiding the dangers Logsdon mentions, if you could reproduce on your own, then your offspring would be an identical genetic copy of you, and quite possibly just as wonderful - another reason to wonder about the advantages of sex.

INSKEEP: Why would you mix up your genes at every generation when, in fact, you can pass 100 percent of your genes on every single time?

PALCA: And yet, nearly all multicellular organisms, and even some single-celled organisms, choose sex. Christopher Wilson is an evolutionary biologist at Cornell University.

M: What we get is females voluntarily sort of submitting their genes to this random lottery that goes on, where only half of them end up in an offspring and half come from the sperm of some unrelated male - who really, in many species, contributes very little else.

PALCA: Very little else - I'm not going to touch that. Moving on - what's up here? What in the world is sex good for? Wilson admits there are some advantages to sex.

M: And the advantage that many scientists have focused on is an advantage against diseases - infectious diseases - parasites and pathogens.

PALCA: The disease advantage comes because sexual reproduction brings in new genes. And John Logsdon says that can make a species hardier and more resistant to microbes.

INSKEEP: Basically, you're shuffling the deck at every generation, and the good cards can come together by doing that shuffling.

PALCA: So sex allows the species to change, and the positive changes help the species survive. But if sex is so good, then what about organisms that can live without it? And now, we come to that creature that's had a really, really long dry spell.

M: No males required for 30 million years - and no sex.

PALCA: Chris Wilson is talking about microscopic, pond-dwelling, bdelloid rotifers.

M: They look like little worms about half a millimeter long with two - sort of rotating electric toothbrush heads on top that spin and filter food out of the water into their little - sort of vacuum-function mouth.

PALCA: And all female. There's a fungus that likes to feed on bdelloid rotifers, but as Wilson describes in the current issue of Science magazine, the rotifer has a remarkable defense.

M: They enter a state that's called anhydrobiosis; that's life without water. And they essentially become little, inanimate dust particles.

PALCA: They're so desiccated in this state that there's nothing for the fungus to eat. And because the bdelloids are now nothing but dust, they can blow away with the wind, with luck landing in a new, fungus-free pond.

M: By playing a game of hide and seek with the parasites, by constantly moving to new habitats, the rotifers can outrun their parasites without needing the variation that sex would provide.

PALCA: So there you have it: Reduce yourself to dust, and you can avoid sex. But wait. John Logsdon isn't totally convinced that bdelloid rotifers never have sex.

INSKEEP: Absence of evidence is not evidence of absence.

PALCA: In other words, just because nobody's ever seen a male rotifer, that's not proof they don't exist. Maybe they show up so rarely researchers just haven't been patient enough. Or maybe they don't like being watched. Logsdon thinks that every creature that's evolved enough to have a cell with a nucleus should be capable of sex. And rotifers definitely have cells with nuclei.

INSKEEP: So I'm agnostic on sexuality or asexuality in bdelloid rotifers.

PALCA: A-ha. So there's some hope for the bdelloid rotifer.

INSKEEP: Well, you know, there's hope for sex, yes - yeah, if that's what you mean. That's funny.

PALCA: Maybe not so funny for the rotifers.

Joe Palca, NPR News, Washington.

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