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You know that thing where evolutionary psychologists come up with explanations for the way things are - "just so stories" which can't be tested, and which make cultural phenomena, usually to do with sex and gender, sound like the innocent products of nature? Well, this isn't an example of that, but I did smile and thought of the evo psych boys when reading a 1998 article on the hemispheres of the brain. The author, Michael S. Gazzaniga, describes the way the brain (specifically the left hemisphere*) will come up with explanations, even when they're nonsense, because one of its jobs is to create narratives.

This is shown with picture-matching tests on epilepsy patients whose hemispheres have been "split", so that they operate independently. Show the left eye (the right brain) one set of pictures, and the right eye (left brain) a different set of pictures: the left hand points to a shovel, which matches a picture of snow, and the right hand points to a chicken, matching a picture of a chicken foot. Now ask the patient why they chose the shovel; the left brain has no idea why the right brain picked what it did, so invents the explanation, plausible but false, that the shovel could be used to clean out the chicken shed. I've read about similar stuff in Oliver Sacks' writing, where, for example, a stroke patient who lacks insight into their condition - a side effect of the stroke damage - will explain they didn't raise their arm when asked because they didn't feel like it: again, plausible, but false.

Gazzaniga writes that even though the brain is "a collection of devices that assists the mind's information-processing demands", "a collection of highly specialized modules", that's not how we feel - our conscious experience is "integrated and unified". He suggests that's because "the left hemisphere seeks explanations for why events occur" (unlike the right brain, which "does not try to interpret its experience"). Pleasingly, that's exactly what Gazzaniga is doing when he puts forward an evolutionary story about the brain - albeit one that could be tested, I think, unlike many of the "just so stories" of evo psych.

* In right-handed people, like me. For simplicity I've stayed with this anatomical set-up through this posting.

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Gazzaniga, Michael S. The Split Brain Revisited. Scientific American [no] July 1998 35-39.

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