Tuesday, July 13, 2010

Social behavior?

We are in northern France this week, in a zone where the main trench-warfare lines moved slaughteringly back and forth for several years. You can't avoid the massive cemeteries from the world wars everywhere you turn. This is sobering enough in and of itself -- a British cemetery near our B&B is well-maintained, the gravesite of 2000 British and Canadian soldiers from World War I, buried beneath uniform white headstones, a minority named, somewhat more of identifed regiment, all "Known Unto God". A few miles down the road there's a much simpler German cemetery for the losing side (pictured), where the remains of up to four soldiers are marked by a single wooden cross.

We're near now to where the D-Day landings took place 20 years or so after the first World War (the 'war to end all wars'). Here, too, are consecrated grave sites of Allies and Axis fallen. In both cases, the scene is now peaceful, green, with flowers and birds chirping. It's hard to comprehend what it must have been like, in either area, with corpses (human and otherwise) everywhere, the landscape barren of healthy trees, plants, or birds, buildings wrecked, the ground pitted with shell-holes. How can people do this to each other? And themselves?

Coming here from the EED meeting, it's impossible not to draw connections with some of the work we heard about there. In particular, Chris Thompson's talk on the social life of Dictyostelium (a model organism often used in evo-devo circles, and a creature we blogged about some time ago), in which cells live separately until the food supply is depleted, and then mass together to eventually reproduce by building a fruiting body that releases new spores when it matures.

Thompson's interest is in how the cooperation this requires evolved. He described how some species lose (voluntarily) more than others -- the cells at the front of the aggregation die at a much higher rate than those at the rear, and thus they don't contribute to the next generation, except in as much as they are genetically similar to those that do. Some species, as Thompson put it, don't do the hard work (of apoptosis), and benefit at a higher rate from the sporulation process. That is, their fitness is higher than that of other cells. They 'cheat' to get reproductively ahead. How did this evolve? (Of course, as there is still remarkable variation in the cheater trait, clearly it's not all that successful of a strategy.)

Is it stretching it too far to make an analogy between Dictyostelium and the soldiers of WWI and II? Each of the soldiers buried in the cemeteries across Northern France gave up his life for a greater good, so to speak. It's not simply allegorical to say that each of the soldiers was similarly part of an organism, an army, that survived even after the death of a given soldier (or even a million soldiers). Each soldier was responding to orders from above -- external signals of a sort he was primed to respond to -- but died within an immediate local context, just as Dicty cells are responding to signals from neighboring cells, including signals that induce some of them to commit suicide at the appointed hour.

Each soldier presumably did know what he was fighting for, at least in theory, but it didn't matter what he knew or why he did what he did. All that mattered was that he killed and was killed, and yet the organism -- the army, and the nation -- lived on. Yes, an army has a central command, but we don't think it's not too far-fetched to consider the evolution of chemical signals as equivalent to the central command in how Dictyostelium live and reproduce.

Evolution has trained and constrained the genome of these particular cells to respond to signals the way they do, to live and reproduce or die as a result, just as the evolution of human consciousness allows a soldier to be trained to let himself be killed. In one case, culture and the mind define the greater good, and in the other it's the successful perpetuation of the species. But they have a lot in common, including signaling, cooperation, cheating, and the sacrifice of individual components of the organism in the perpetuation of the whole. Indeed, a major point we try to make in our book is that a similar logic of causation, based on information exchange between semi-autonomous, partially isolated units, is a pervasive characteristic of how life works.

We'll leave this analogy between humans and Dictyostelium at that though, because we don't want to push it to the point of suggesting that all human behavior is built in. To us, as we've said numerous times before, most evolutionary explanations of human behavior are unconvincing; people can talk themselves into all manner of things, no matter how much it curtails their fitness (going to war, suicide bombing, induced abortion, celibacy are just a few examples), and darwinian explanations just don't fit such things, except in some theoretical ways under very specialized conditions. Not to deny that how these kinds of behaviors evolved may certainly be interesting, and important, but explanations are often forced to fit a preconceived idea (such as that of inclusive fitness, for those familiar with the argument in evolutionary behavior).

But we just couldn't leave these similarities unremarked as we travel through Normandy with echoes of evo-devo in our heads.

1 comment:

GGreene said...

In a prior job, I was responsible for an operation in France, so I spent a month or more a year there. One Sunday, the Manager of the plant escorted me to the Normandy beaches and the American cemetery. I found the place and the experience profoundly moving. I'd love to see it again.