Why has synesthesia survived throughout human evolutionary history?S

An estimated 4% of the population have synesthesia, a condition where senses become confused. People with synesthesia may perceive that certain sounds have flavors, or that certain words have a specific color. Even though synesthesia is widely recognized, and at least vaguely understood, what we don't know is why it happens. Is there an evolutionary advantage to it? Is it something that's survived because it's associated with a useful feature? Or is it simply too harmless to be selected against?

Synesthesia is thought to be tied to an excess of neural connections between parts of the brain — like say the areas associated with reading letters and with colors. For some people, the condition has been linked to improved memory, but new research from UC San Diego points to more than that. This new work looks to the link between creative fields and synesthesia — artists, writers, musicians and their ilk are around 7 times more likely to have the condition.

Researchers David Brang and V. S. Ramachandran think that synesthesia may have a "hidden agenda," one that improves the world's artistic legacy. They think it's linked to increased creativity and a greater ability with metaphors. In other words, it makes people more artistic, which is a feature that our population selects in favor of, which explains why it's survived.

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