Why human colour vision is so odd (physiology)

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https://aeon.co/ideas/the-red-and-green-...-is-so-odd

EXCERPT: Most mammals rely on scent rather than sight. [...] Most other mammals have two different types of colour photoreceptors (cones) in their eyes, but the catarrhine ancestor [of primates] experienced a gene duplication, which created three different genes for colour vision. Each of these now codes for a photoreceptor that can detect different wavelengths of light: one at short wavelengths (blue), one at medium wavelengths (green), and one at long wavelengths (red). And so the story goes our ancestors evolved forward-facing eyes and trichromatic colour vision – and we’ve never looked back.

[...] Colour vision works by capturing light at multiple different wavelengths, and then comparing between them to determine the wavelengths being reflected from an object (its colour). [...] Our own vision does not have this even spectral spacing. In humans and other catarrhines, the red and green cones largely overlap. This means that we prioritise distinguishing a few types of colours really well – specifically, red and green – at the expense of being able to see as many colours as we possibly might. This is peculiar. Why do we prioritise differentiating red from green? Several explanations have been proposed.

Perhaps the simplest is that this is an example of what biologists call evolutionary constraint. [...] Another explanation emphasises the evolutionary advantages of a close red-green cone arrangement. [...] A final explanation relates to social signalling. [...] Recently, my colleagues and I tested this hypothesis experimentally....

MORE: https://aeon.co/ideas/the-red-and-green-...-is-so-odd
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