WORLD SCIENCE

"Long before it's in the papers"
May 09, 2005

Posted April 9, 2005
Courtesy Nature
and World Science Staff

Why do we bother with sex? Although it seems obvious to us, it’s a longstanding puzzle to biologists why nature favors this mechanism of reproduction, at least for most advanced organisms.

Sex is time-consuming, exhausting, even dangerous. The genetic jumbling involved means that favorable combinations of genes are forever at risk of being broken up. Also, the fact that sexual organisms must pair up to create each offspring makes them reproduce half as fast as competing creatures who can reproduce without sex.

Now, researchers have produced evidence to back up a 19th-century theory about sex: that nature favors it because it allows faster evolution. 

Evolutionary theory states that organisms with the best genes for survival and reproduction spread faster, and thus spread those genes further, than their competitors. This, together with the fact that new genes crop up through mutations, allows new species to evolve. 

August Weismann, a 19th-century German biologist, proposed that sex exists because it shuffles genes, creating a greater variety of them for evolution to work with. 

An experiment with yeast bore out this idea, the new study found.

When the going gets tough, yeast that have sex are much better at adapting to conditions than their non-sexy counterparts, the research found. The study, by Matthew R. Goddard of the University of Auckland, New Zealand, and colleagues, was published in last week’s issue of the research journal Nature. 

Yeast don’t quite have sex as we would recognize it. But they can, optionally, reproduce in a sexual way: creating specialized cells that fuse to form a new generation, much as sperm and egg cells fuse as a result of animal sex.

The researchers created a mutant strain of yeast that cannot divide into sexual spores. In stress-free conditions, the mutant strain performed as well as normal yeast. But at higher, more stressful temperatures, the sexually reproducing yeast showed a far better increase in growth rate than the mutants as the experiment progressed.

This hints that sex does indeed come in handy when it comes to survival of the fittest, as the genetic shuffling may allow a greater chance that a useful suite of genes will come together. 

But the study fails to answer all the conundrums of mammalian sex, such as why females let males get away with making such small, cheap sex cells, the researchers said. “We are still far from a definitive answer to the question of why sexual reproduction is so common,” wrote Rolf F. Hoekstra of Wageningen University, The Netherlands, in a commentary in the journal. 

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Front image courtesy National Cancer Institute

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