Planet Earth

You Call That Fair?

The LoomBy Carl ZimmerSep 29, 2003 2:56 AM


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Over the past couple weeks an unplanned experiment has taken place that shows what sort of science makes it into the popular consciousness and what doesn't. In the past couple weeks we've had three pieces of research on the same evolutionary puzzle in the same high-profile journal (Nature). One was all over the place--I'll just link the USA Today article as one example. The other two vanished with barely a peep. All three papers tackle the puzzle of kindness. Why do we cooperate when there are powerful evolutionary forces that would seem to work against cooperation? If I waste a lot of my time and energy helping you, I have less time working towards my own reproductive success. And if we do cooperate for whatever reason, shouldn't there be a big evolutionary advantage to cheating--reaping your kindness and offering none of mine? We humans cooperate a lot, but our cooperation is mediated by cultural institutions (governments, religions), and even more so by language. So does that mean cooperation in our species could exist before the rise of human culture and language? Big questions, with many inviting spots into which you can sink your teeth. Frans de Waal of Emory University sinks his teeth into monkeys and apes. He has argued for a long time that many primate species cooperate in very complicated ways. If he's right, the roots of human cooperation were already in place millions of years ago, in the common ancestor we shared with other primates. Human cooperation depends in large part on our strong sense of fairness. It's common for people in any culture to get mad when they don't get their fair share, or when they see someone else getting cheated. Well, as de Waal and fellow Emory primatologist Sarah Brosnan reported last week, capuchin monkeys get mad, too. They trained the monkeys to perform a simple exchange: they gave the monkeys a token, which the monkeys then returned in exchange for a cucumber. The capuchins learn fast how to play the game. But if they saw that another capuchin was getting rewarded with better stuff--i.e., a grape--they might heave back the cucucmber, or refused to give up the pebble. Watching another capuchin get rewards for doing nothing made them even crankier. The press was all over that one. The New York Times ran an editorial about what capuchins can teach us about making America fairer. Now I'm all in favor of Frans de Waal getting attention, since his work is so fascinating. Capuchins are a lot more distantly related to us than chimpanzees, so we could be talking about a sense of fairness dating back 30 million years in our ancestry. But I don't think the attention actually corresponded that much to the importance of his work. If people really are interested in the evolution of cooperation, they should have been just as interested in a couple wonderful papers that Nature published two weeks earlier. Those scientists did something more than observe cooperation. They watched cooperation itself come into being. Instead of capuchins, the authors of these studies work with bacteria. Bacteria may not help at barn raisings or drive on the right side of the road, but many species are incredibly social. The soil bacteria Myxococcus xanthus are the Roman army of the microbial world. Instead slithering alone through the muck, hundreds of thousands of the microbes join together to lay down a matrix of fibers several inches wide. Then the bacteria race around the network in great swarms, skittering along the fibers with their glue-tipped legs. Any individual bacterium could sneak along the network without helping build it, but most M. xanthus make the sacrifice for the collective. Greg Velicer and Yuen-tsu Yu knocked out the gene that makes the main protein in the glue-tipped hairs of M. xanthus. Suddenly, the bacteria couldn't use their highways. They could still move around by themselves with a back-up transportation--they glide slowly on a carpet of goo that they shoot through holes in their membranes. But after a few months, the bacteria started building networks and swarming again. Studies on these bugs showed that they had picked up several mutations during that time, evolving a new way of building their highway system. (The picture of the petri dish at the top of the post shows all the stages of the process. The cloud at the top of the dish is a wild-type colony. The two little clumps are mutants who can't form networks. And the squiggly psychedic fireworks at 2 and 8 o'clock are re-evolved matrix builders.) Paul and Katrina Rainey, two New Zealand scientists, reported on another matrix created by Pseudomonas fluorescens, a species that feeds on organic matter. They put P. fluorescens in a beaker of broth, and before long a mutant strain began to emerge. Instead of floating in the broth, the mutants create a mat on the surface. (The mutants are called "wrinkly spreaders.") By living in this new spongy habitat, the wrinkly spreaders can consume lots of oxygen from the air while still enjoying the organic matter in the broth. The Raineys also found that after a while, cheaters evolve to take advantage of the wrinkly spreaders. These guys live in the mat without contributing to it, and actually thrive more than the wrinkly spreaders themselves. These cheaters can actually doom the entire colony, because their dead weight makes it easier for the mat to sink to the bottom of the beaker, where they can't get any oxygen and die. I don't think it's just geekiness on my part that makes me think that these projects are as cool as de Waal's irritated monkeys. And yet I can find barely a nod to them in the press. I suspect that people are drawn to de Waal's work for two reasons. One: the monkeys are cute. Two: it's easy to look at the monkeys like animals in Aesop's fables, dramatizing human nature. But capuchins aren't metaphors for progressive tax codes or faith-based initiatives or whatever platform someone's pushing. The research on them is important because it gets at evolutionary principles, at the way moral systems can be encoded in emotions rather than computed by reason. And the bacteria papers are just as important because they show how even microbes can find a payoff in working together. In fact, these studies are arguably more important, because cooperation comes into existence time after time, showing just how powerful an evolutionary force it can be. (And it also is another headache to those who would say that something like cooperation could never evolve. Which is always a plus.)

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