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It's not just advanced species that eat their own

Posted on: Monday, 11 August 2003, 06:00 CDT

It's not just advanced species that eat their own

By DONALD G. McNEIL JR. New York Times

Monday, August 11, 2003

New York Times

Birds do it. Robber flies that look like bees do it. Even chimpanzees do it.

Now researchers say that a tiny voice from near the bottom of life's evolutionary ladder is chiming in on the chorus: Let's do it. Let's eat our own.

It is time to get over the old notion that only advanced, highly intelligent beings practice cannibalism.

It has just been discovered by Harvard and Madrid researchers that even bacteria do it.

Higher orders, like humans, may practice cannibalism for complex psychological reasons, like appeasing gods or honoring ancestors. Chimps seem to do it as an act of revenge or in a burst of malice: Females have been known to snatch and eat the babies of smaller females. Lions do it for genetic preservation: When a male takes over a pride, he eats the previous king's cubs, eliminating the old royal bloodline and speeding the lionesses back into estrus to continue his.

For praying mantises, it's just about good sex. As the finale to a successful copulation, the female bites the head off her mate and devours him. It's not known if the plat du jour sacrifices himself so his offspring will be nourished, or if he entertains naive hopes of escaping before the big chow-down.

Bacillus subtilis bacteria, though, act more like the Donner Party. They use cannibalism only in extremes, and only for survival, according to a study that appeared in Science earlier this summer.This mild relative of the anthrax bacterium engages in what could be described as cannibalism for couch potatoes: It takes the path of least energy.

Its other option for surviving starvation is to turn itself into a hardy spore, as anthrax does, but that means taking 10 hours to build a thick cell wall and eject the water in its interior.

"It becomes like freeze-dried food -- almost crystalline, resistant to heat and time and radiation," said Richard M. Losick, a molecular biology professor at Harvard and one of the study's authors.

But should its dirt environment suddenly become enriched with the organic matter it needs to survive, a spore is at a disadvantage because it takes 36 hours to morph back into a bacterium.

For B. subtilis, the lazy alternative is to pump out an antibiotic that pops open its brethren so it can digest their innards, which is what Losick and a team from the National Biotechnology Center in Madrid, Spain, caught it doing.

This seems to be the lowest order so far that engages in cannibalism, Losick said.

What B. subtilis gets is a fraternal snack to tide it over in the hopes that dinner will arrive. Who eats whom is "just by chance," Losick said. "Some start down the road faster than others."

The prion connection

Human cannibalism did not happen by chance, of course, though social scientists debate how common it was. Around the world, sites have been found with defleshed skulls, bones with shiny "pot polish," femurs cracked for marrow and even one set of petrified human feces with traces of human muscle in it.

In April, a powerful argument that cannibalism was widespread among our ancestors was made by researchers from University College, London, and from Australia and Papua New Guinea.

They found that all ethnic groups harbor genetic signatures that protect against infection by prions, proteins in meat that lay waste to the brain. Prions can come from animals, as mad cow disease showed, but they kill off cannibals far more effectively.

The best-known example of that is the Fore people of Papua New Guinea, who from the 19th century to the late 1950s held "mortuary feasts" on deceased relatives.

From the 1920s to the 1960s, an epidemic of kuru, a prion disease, killed more than 200 Fore a year, especially women, who ate brains while men ate muscle. A study of 30 elderly Fore women who survived the era showed that 23 had the prion-protection gene, which was far less common among Fore born later, suggesting that it had protected them.

The discovery of similar genes in ethnic groups around the world, the researchers said in the April paper, is powerful evidence that cannibalism had at some time made such protection important.

It should be noted that forms of human cannibalism still go on. "Muti murders" are well-known to the South African police.

Studying lower species is, at least, less fraught with political touchiness. Researchers who believe that the Anasazi people of the American Southwest widely practiced cannibalism have been accused of racism by the descendants of the Anasazi, the Hopi.

But lower-order cannibalism, not driven by emotion or religion, is in some ways more of a puzzle.

Presumably, it confers some evolutionary advantage, but it seems such a backward-turning gear in the Darwinian drive train. After all, each cannibal has just as good a chance of being eaten as of eating. That ensures survival of the fittest, but ultimately of only one fittest -- not an ideal species-preservation goal.

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