Saturday, July 26, 2008

Cheating, Sex, and Crafty Bacteria

I have been reading a fascinating new book, MICROCOSM, by Carl Zimmer (who also wrote the terrific PARASITE REX). MICROCOSM is everything you ever wanted to know about the bacteria E. coli, and much you never suspected. Just one example: Some E. coli cheat.

Cheating has been a big topic in evolutionary biology in the last ten years. Everybody does it: birds, mice, college students. The basic idea is this: A mechanism evolves because it confers an evolutionary advantage. Some birds, for instance, pair-bond, either for a mating season or for life. The advantage is an increased chance of getting their little birdy genes into the next generation because the offspring have a better chance of survival with two parents. Some female and male birds, however, cheat. Unknown to their partners, they sneak off and have sex outside the pair bond.

Ornithologists have had a field day (sorry) documenting which birds cheat, when, and with whom. But it turns out that E.coli cheat on the social contract, too. This concerns not sex (bacteria all have wild sex lives, swapping gene-laden plasmids like political candidates passing out lapel buttons), but rather communal feeding. When food is scarce, E. coli can shut down their protein-making machinery and go dormant. Most do. But a few delay shut-down and then eat their fellows, a sort of microscopic Donner Party right there on the lab slide.

This is not, of course, a conscious decision on the part of bacteria. It can happen because genes -- all genes -- don't operate in regular rhythm. As Zimmer puts it, E. coli "may spit out six ...enzymes in the first hour, or none at all." The bacteria with none at all don't shut down as soon, get a source of food in the form of those that do, and can go on breeding. When any other survivors revive, they find a colony dominated by the cheaters. It's exactly like a physics student who has illicitly the answers to a test beforehand; he will come out on top by not behaving according the social contract.

This book has set my mind to ruminating on several possible SF stories. E. coli as cheaters. E. coli as biofilm builders. E. coli as communicators.... E. coli as models for alien societies. I used bacteria this way once before, in the PROBABILITY series, but now I know much more detail. Stay tuned.


Orion said...

Biology has uncovered some fascinating links between sexual dimorphism and the strength of pair-bonding. A good rule of thumb is the more alike in size, strength and appearance the two sexes are, the stronger the bond, and the less outside cheating. In particular, if the male is larger and showier, it's a good indicator that he's looking for a harem, not an exclusive mate.

Humans appeal to fall on the same curve. Men are larger and stronger than women on the average, and well-differentiated in their secondary sex characteristics, but not outrageously so. It's sometimes difficult to filter out the cultural component, but across many societies the general trend seems to be that human males look for one live-in mate, and as many outside dalliances as they can get away with.

Hmmm. I can just see this argument turning up in a divorce court in the near future. "My biological imperative caused me to take a mistress, Your Honor!"

Bill Dunning said...

Zimmer always writes about the most fascintating stuff. If I were a writer, his books and blog would be a never-ending source of story ideas for me, I'm sure.

Haven't read this one yet though....