Monday, February 04, 2008

The slime of the Earth

Long time visitors to Science Musings may recall my paean to the amoebic creatures called slime molds. In that essay I wrote:
But wait. Watch. Observe their streamings and slitherings and towerings. They are a mass of individuals. They are a society. They blossom like flora. They creep about like fauna. They are plant and they are animal. And neither. They embody in their life cycle the history of life, and the history of our race. They are charged full with animation.
Slime molds are one-celled organisms that in the course of their life cycle band together and specialize in what is to all intents and purposes a multicelled fruiting body -- in a curious way recapitulating the history of life on Earth.

And now it turns out we can add another talent to the strange list of the slime mold's accomplishments: memory!

According to a report in the January 23rd issue of Nature, a team of researchers in Japan have demonstrated that slime molds learn from experience. The rate at which slime molds move varies with the humidity of the environment; they slow down in drier air. The Japanese researchers gave the organisms hourly "shocks" of dry air, and watched them slow down. When the shocks stopped, the slime molds continued to slow down on the hour, as if they were anticipating the next regular shock. This behavior persisted for several cycles before the memory faded. The Japanese say that their findings "hint at the cellular origins of primitive intelligence."

Well, we'll see. A result so startling needs confirmation. But if true, we have a gooey colony of slime picking up a rhythm, learning a beat.

In that earlier essay, I wrote:
There is a sense, I suppose, in which you and I are slime molds of a sort, accretions of trillions of cells that have banded together and specialized for the purpose of producing sperms and ova. The essence of life is to make more life. Over an over again in the history of life the efficiency of reproduction has been aided by collaboration, symbiosis, even altruism.
And, of course, by learning and memory.