Wednesday, December 02, 2009

Are men necessary?

Quite some some ago, James Thurber and E. B. White wrote a classic little book called Is Sex Necessary? More recently, Maureen Dowd refined the question with a book called Are Men Necessary? From a biological point of view, if you are going to get rid of sex, it's the males who will be bumped out of a job. In fact, many species of plants and animals get along quite nicely with self-fertilization.

As Aneil Agrawal writes in the 19 November issue of Nature: "On the face of it, self-fertilization is the efficient way to breed: compared with outcrossing [two parents], there's usually much less fuss, for a start. So why isn't reproduction by selfing far more prevalent than it is?"

It's a perennial question, one that has befuddled evolutionary biologists ever since Darwin. Self-fertilization eliminates the dangerous, difficult and chancy business of finding a mate. One parent -- usually the female -- makes the largest investment in bearing and raising the young. Males, who don't bear offspring, would seem to be an unnecessary "cost" in reproduction. Why in the world did natural selection invent two sexes?

As Agrawal writes: "Among the hypothesized benefits of outcrossing are that it reduces the effects of deleterious mutations, or that it improves the ability to adapt to changing environmental circumstances." A mix of two sets of genes -- outcrossing -- is better than one.

Agrawal's article is by way of introducing a report in the same issue, by researchers at the University of Oregon, that demonstrates quite tidily the advantages of genetic exchange.

They worked with the little nematode worm Caenorhabditis elegans that I've written about here many times before. About a millimeter long, as thin as spider silk And just 959 cells. Exactly. About as simple as an animal can be and still be manifestly an animal. Wild-type populations of C. elegans exhibit a low to moderate level of outcrossing.

Our researchers started with two mutant strains of C. elegans, one exclusively outcrossing, the other exclusively selfing. They put them into novel and challenging environments -- a physically rugged terrain, and an environment laced with bacterial pathogens. In both cases, after 40 or 50 generations, the outcrossers had adapted nicely to the new circumstances, the selfers not at all.

What's good for the worms is presumably good for us too. Maybe males are useful after all.