Do hash functions exist in nature?

Given that there are quite a few bioinformaticians around these days, wondering if any of you 开发者_如何学JAVAhave seen examples of hash functions (or mapping mechanisms) occuring in nature? And if so how do they work?

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Smell is a sort of hashing.

A smelling hash function transforms a huge variety of chemical compounds to a small piece of information (several things may smell alike). Living organisms learn to distinguish the "buckets" such "hashing" puts the objects to, and tend to infer behavioral patterns that rely on such a function.

This applies to taste as well.

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On a more humorous note, I would say that the nervous and sensory systems of most or all animals might be seen a hash function designed to divide things into:

1. things to mate with
2. things to eat
3. things to run away from
4. rocks.

Kudos to Terry Pratchett for identifying this elaborate system of categories. ;)

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The visual system (lens, retina, cortex) is a suite of serially composed hashing functions.

(1) projection from 3d to 2d. (2) photon to neural stimulus (3) spatial to pattern (4) spatial and pattern to temporal (5) (in predator species with aligned pairs of eyes) two sets of all the above back to 3d. etc.

Hubel and Wiesel got the Nobel in 1981 for figuring this out at the expense of a bunch of kittehs. They didn't call them hash functions, but that's actually a terrific way of representing them.

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I guess turning a color image into a B&W one could be see has a mapping/hashing -- and such filter exist in the nature for photography.