Saturday, December 25, 2010

Our Brain Is Ready For This

I thought that would be a better title than my first idea: "The Difference Between the Baldwin Effect and Neuronal Recycling." Please don't let either title scare you, the concepts are easy to understand and fascinating.

A Baldwin effect is when the brain evolves not a specific behaviour, but the ability the learn some specific kind of thing. For example, our ability to learn language might be a Baldwin effect. I didn't evolve to speak English, but I evolved to be able to speak something. Evolution provided children with the ability to quickly learn whatever languages we are exposed to. It was able to do this because a language-using culture was reliably present during development.

Walking might be another example. Are we evolved to walk, or are we evolved to learn to walk? If it's the latter, which seems likely, it's possibly a Baldwin effect.

I have recently been reading about another interesting idea that might be confused with the Baldwin effect. Neural recycling (Dahaene & Cohen, 2007) is when a cultural artifact (e.g., writing) reliably takes advantage of the best part of the brain for it. Let me explain.

Writing only appeared about 5400 years ago. This might seem like a long time, but scientists accept that this is too short a time for a species to evolve a new brain structure. It's only 270 generations. Many scientists see this as evidence that we have a general-purpose learning system. After all, if we all can learn to read, and our ability to read could not have evolved, then a generic learning mechanism must be in place.

The mystery is this: the same part of the brain* ends up getting used to read, no matter who it is! This is very curious. If we have a general purpose learning system, and I think we do (Stanovich 2004), then where reading ends up should be in different places in different people. No one place would be better than any other.

The neural recycling idea is that things like reading end up in the parts of the brain that they do because those parts were evolved to learn things that are kind of like reading. That's the recycling part. To make an analogy, mug handles were not designed to keep tea bag strings from falling into the cup, but many people use it that way.

What might the reading area have evolved for? One possibility is that it specializes in detecting patterns of two or three lines. To quote Dahaene and Cohen (2007):

Changizi and collaborators have recently demonstrated two remarkable cross-cultural universals in the visual properties of writing systems (Changizi and Shimojo, 2005; Changizi et al., 2006). First, in all alphabets, letters are consistently composed of an average of about three strokes per character (Changizi and Shimojo, 2005). This number may be tentatively related to the visual system’s hierarchical organization, ...

The difference between these two effects is that a brain area made with the Baldwin effect was evolved for a particular learning experience (the historical origin of language occurred long before the creation of written language). In neural recycling, a cultural artifact is taking over something evolved for another purpose (perhaps with the Baldwin effect).

* the occipito-temporal area

Pictured: Tea of different colors. 


Changizi, M.A., and Shimojo, S. (2005). Character complexity and redundancy in writing systems over human history. Proc Biol. Sci 272, 267–275.

Changizi, M.A., Zhang, Q., Ye, H., and Shimojo, S. (2006). The structures of letters and symbols throughout human history are selected to match those found in objects in natural scenes. Am. Nat. 167, E117–E139.

Dehaene, S., & Cohen, L. (2007). Cultural recycling of cortical maps. Neuron, 56(2), 384-398.

Stanovich, K. E. (2004). The Robot's Rebellion. The University of Chicago Press: Chicago, London.

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1 comment:

Jim Davies said...

There's a further distinction that should be made: and "exaptation" is when something evolved for one function eventually gets used for another. A good example is bird feathers. At first, they evolved for temperature regulation, but eventually were used for flight.