Bred for Agression

Nicolas Wade once again identifies some meaningful research and makes it available to the general reader. If such work in neuroscience and genetics shows how brains, including human brains, predispose us to certain kinds of productive or counterproductive actions, why don't our modes of intervention (including, of course, punishment) reflect such findings? We are caught in a vicious cycle where adverse environments reinforce genetically influenced behviour. This is cause for much pessimism, particularly since a whole welfare industry with a vested interest in maintaining the status quo tends to frustrate achieving any real modification, if modifications can indeed be made in laissez faire societies....


October 10, 2006 ~ The New York Times

Flyweights, Yes, but Fighters Nonetheless: Fruit Flies Bred for Aggressiveness

By Nicholas Wade

What can stand on its hind legs and duke it out with its front feet, boxing and tussling like a four-armed pugilist?

The answer: a strain of laboratory fruit flies bred for shameless aggressiveness toward their own kind.

These miniature gladiators flail at each other with a zeal and tempo that make professional boxers look like milquetoasts. A video shows a Drosophilan version of Mike Tyson forcing an opponent to fly the ring.

The fighting flies have been bred by Herman A. Dierick and Ralph J. Greenspan, two biologists at the Neurosciences Institute in San Diego. Their goal is to discover the neural circuits that are genetically modified when flies develop aggressive behavior.

Fruit flies in the wild are quite hostile toward one another. Males will fight off other males from prize real estate, like a rotten peach, where females like to congregate. But when kept in the laboratory, subsequent generations soon become domesticated.

Dr. Dierick and Dr. Greenspan figured that since this behavior was easily lost, it should be easy enough to regain if the right selective pressure were applied. So they took a laboratory strain of tame fruit flies and set up pots of food that could be protected by single males.

The males that fought the hardest in these encounters were sucked off their little arenas with a pipette and rewarded by becoming the fathers of the next generation.

More aggressive males started to appear after only 5 generations, and by the 21st generation, Dr. Dierick found that the aggressiveness of male fruit flies had increased more than 30-fold, according to a scoring system he developed.

At this point he was able to perform an experiment that would have been quite messy had he been working with larger animals. He chopped off the heads of 100 aggressive individuals, ground them up and ran a test to measure changes in the activity of their brain genes.

About 80 genes — the fruit fly has about 14,000 — were either more or less active in the brains of the aggressive flies, compared with flies of the original population from which they were selected.

Two of the most changed genes were ones involved in the detection of pheromones, the hormonelike scents with which fruit flies signal their activities.

One of these genes seems to make the aggressive flies unusually sensitive to the pheromones emitted by other males. Another, which is repressed in the aggressive flies, mediates sensitivity to the pheromone with which male flies mark their territory. The aggressive flies seem less able to recognize others' boundaries.

Dr. Dierick hopes to identify the neural circuit in the fly's brain that mediates aggressive behavior and that is modulated up or down by inputs from pheromones and other sources. Dr. Greenspan said an understanding of how genes set up circuits to govern behavior would be of broad significance in understanding what makes either flies or people tick.


  1. Anonymous8:26 PM

    The 30 generations model seems about right for producing a type of trait in a species/rate. Hence the plausibility of the Harpending Cochrane thesis about the intellectual prowess of Ashkanazi Jews whose superior mental acumen came with aggressiveness, bargaining skills, verbal dexterity, and clever humor, all in the course of 600 years.


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