Daniel Koshland, Jr.
(1920-2007)
Daniel E. Koshland was an American biochemist, a professor at the University of California, Berkeley, and from 1985 to 1995 the editor of
Science magazine, a publication of the American Association for the Advancement of Science, of which Koshland was a member.
Koshland's work included a study of bacterial chemotaxis, how single-celled organisms moving through the environment can sense temperature and chemical composition gradients. If nutrients are increasing in the direction of motion, or others conditions are more favorable, the bacterium continues. If not, the rotation direction of its tiny flagella reverse. Rotation
of the flagella counter-clockwise drives the bacterium straight
ahead. Flagella rotating clockwise cause the
bacterium to tumble and face in random new directions.
Their sensors and
motion capability let them make
two-stage decisions about
which way to go. As the bacterium moves, receptors on the bacterium surface detect gradients of chemicals. When the gradient indicates
“food ahead” or “toxic behind,” the bacterium keeps going. If the
gradients are not promising, the bacterium reverses the flagella
rotation direction, which makes it tumble again.
This combination of randomizing its direction (generating
random possibilities), followed by an
adequately determined decision to continue (or not) is a primitive version of the
two-stage model of human free will.
References
Bacterial Chemotaxis as a Model Behavioural System. New York: Raven Press.
Normal |
Teacher |
Scholar
|
|
|
