Living Columns & Blogs

More than 1 way to do it

Those of us who’ve been around for a few decades have seen friends or familyengulfed in bitter custody disputes.

There’s nothing like denouncing the other parent of your children in open court (and paying steep legal billsfor the privilege of doing so). Custody clashes are clearly only the tip ofthe iceberg of the total cost we sometimes pay for sexual reproduction.

From a scientific point of view, there’s another problem with sex -- and it’sa doozy.

Some primitive animals can reproduce either sexually, with a partner, or allby themselves. This means that in some species, females can mate with males,while other females simply reproduce all by their lonesome. Snails can doexactly that trick. If a female creates baby snails by herself, theoffspring are identical clones of the mama snail.

Wait a minute, you say, you’ve never heard of natural “clones” like that,only special man-made clones like Dolly the sheep.

But actually, you yourself may well have cloned a creature in the plantkingdom, simply by taking a cutting of a plant and letting it root. The newplant is genetically identical to its parent, making it a natural clone.

Now think of a lake full of snails. If a particular female mates with a malesnail and produces 100 eggs, she might have 100 babies that are 50 percentmale and 50 percent female. Her genes will be in all the babies, along withthe papa’s genes.

But if a female snail reproduces by herself, she can create 100 babies thatare all female and all carry only her genes. Basically, this route puts moreof the female’s genes into her offspring. Way more!

If evolution is all about surviving and getting your genes into the nextgeneration, it looks like females reproducing on their own should have takenover the whole planet long ago.

After all, it’s not so easy to reproduce sexually. You have to find apartner, and that can take some doing (if you are a rare bird, for example).Attracting a mate can be a very big deal, with a big investment of time andenergy (think of the peacock). Beyond that, both male and female must do theright things and both must be fertile at the same time.

Compared to that, self-cloning starts to look easy and much more likely tobe successful. Why are we not all cloned females reproducing identicalcopies of ourselves?

Professor Mark Dybdahl of Washington State University is a biologist whoinvestigates that fundamental question.

“There’s got to be something in ecology or evolution that favors sexualreproduction,” he said to me recently.

Think for a moment of an Iowa cornfield,planted with a particular strain of corn, all the plants being geneticallyidentical to one another due to inbreeding. Because the plants are the sameand genetically programmed to create high yields, the farmer may well getmany, many bushels of corn from his field.

But if a disease or parasite arises that can feast on that particular strainof corn, disaster results.

Here’s the key concept: sexual reproduction is unlike cloning because itcreates offspring that are different from one another. It can be well andgood to be a female snail that reproduces exact copies of her own snailyessence. But that’s useful from an evolutionary point of view only ifnothing comes along that can wipe out all of her identical descendants.

“A female snail that reproduces sexually creates offspring that are varied.That increase the chances that some of her offspring can resist problemslike parasites or disease,” Dybdahl said.

Dybdahl’s work has nailed down quite a bit, at least in the realm of snails.

“The snails that reproduce sexually -- and pay the costs of having sex -- dowell only when parasites are beating the clones down,” he said.

I don’t know about you, but nobody taught me any of this material in middleschool sex ed class. You have to keep learning well into middle age toreally get to the basics -- such as the fundamental reasons that lie behindfamily court.

* E. Kirsten Peters is a native of the rural Northwest but was trained as a geologist at Princeton and Harvard. Questions about science or energy for future Rock Docs can be sent to epeters@wsu.edu. This column is a service of the College of Sciences at Washington State University.

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