Saturday, December 21, 2013

Meet the beaver

My theory of animal cognition began many years ago when my wife and I were studying beaver. I was working my way through grad school by designing earth dams for the US Government. Beavers build earth dams so naturally I was interested.

What I discovered was that a beaver dam is very different from a human dam. In fact a beaver dam is more like a bird's nest. A human dam is a big pile of carefully selected and compacted dirt. A beaver dam is typically a lattice of sticks supporting an upstream face of dirt. One advantage of this design is that it uses a lot less dirt than a human dam does. Another is that it does not wash away when water flows over the top, as human dams tend to do.

Presumably the beaver knows how to build these elaborate structures by instinct. But what I realized while watching them work is that a great many decisions have to be made along the way. These decisions involve the specifics of the local situation, so they cannot be merely instinctive.

For example, knowing how to build a dam does not tell the beaver which stick to use next. Or which tree to fell and how to cut it up to get that stick. Or where to get the next armload of mud. Or where and how to put these items into the structure. These specifics cannot be in the DNA, as it were.

The point is that the beaver must have elaborate sets of concepts in order to perform these elaborate tasks. So do birds and so do horses. It is easiest to see this when we know what the critter is doing. Speaking of which it is an interesting question why beavers typically build many dams in one place, not just the one their lodge is behind. I think I have a surprising answer to this question but that will be another posting.

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