Worms do calculus to find food. (Um, not really.)
But apparently worms use salt concentration to find food, and tend to head in the direction of the gradient of salt concentration. That is, they go where there's more salt. This is due to neuroscientist Shawn Lockery and his students at the University of Oregon. I think the paper is the following:
Suzuki H, Thiele TR, Faumont S, Ezcurra M, Lockery SR, Schafer WR (2008). "Circuit motifs for spatial orientation behaviors identified by neural network optimization." Nature 454:114-117.
but I can't be 100 percent sure -- Penn's libraries don't allow access to the electronic version of papers from Nature until twelve months have passed, and I'm not on campus right now. (This is, however, the only paper on Lockery's list with a title fitting the description.)
Saying "worms do calculus to find food" seems a bit disingenuous to me, though. It seems like saying that baseball players do calculus to catch fly balls. The larger point, though, is that neural processes -- of worms or of humans -- can be modeled using mathematical techniques, which may be of use to people trying to develop artificial systems that do these things.
(From John Scalzi, via 360. Apparently this first appeared in blogs a couple weeks ago, but I'm posting it here anyway, because it's new to me, which means it's probably also new to a lot of you.)
06 August 2008
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"Apparently this first appeared in blogs a couple weeks ago..."
You got that right!
It's too great of a story to let alone!
Saying "worms do calculus to find food" seems a bit disingenuous to me, though."
Perhaps the above statement is too "harsh." I think that when we use calculus to model any phenomenon, we don't assume or imply that the phenomenon somehow "obeys" the laws of calculus; it only means that the phenomenon allows or permits itself to be modeled by calculus.
Maybe the worms use their own "internal calculus" (perhaps honed by millions of years of evolution) which gives results identical or similar to the ones obtained by using the calculus we are so accustomed to.
Anyway, I guess the larger point that I am trying to make is that calculus is an approximation tool! This is discussed by Alexandre Borovik in his post, titled Commented Out (which sounds a bit unusual!) in which he makes a methodological point about calculus:
"Vladimir Arnold forcefully stated in one of his books that it is wrong to think about finite difference equations as approximations of differential equations. It is the differential equation which approximates finite difference laws of physics; it is the result of taking an asymptotic limit at zero. Being an approximation, it is easier to solve and study."
To conclude, the worms in their search for food are perhaps using some kind of mechanism, which can be modeled quite well by our approximation tool, viz.calculus!
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