Comment by vanderZwan | Hacker News Reader

Comment by vanderZwan | Hacker News Reader

As a colour-blind person, this article both makes sense to me, and at the same time it doesn't.

I have often wondered why human colour vision is not evenly distributed across the spectrum of visible light. This seems like a decent enough model for why that might be the case.

However, that makes it very peculiar that there are so many people with colour-blindness like me, especially if it would be such a strong evolutionary advantage. One would expect selection pressure to have removed those genes from the gene pool by now.

My own pet hypothesis is that it has to do with humans being a social species. For us, individual specialisation has much bigger evolutionary benefit, since it is shared, and a lower evolutionary cost, because other members of the group can compensate for shortcomings.

To give an overly simplified "economic" model of it: when we collaborate properly, the net performance of a group is not the average performance of all members, but the sum of the maximum performance of individuals.

So back to colour-blindness. It is fairly well-established that dichromatic colour-blindness helps see through certain types of camouflage. In a hunter/gatherer society, having one member of the group who is good at spotting prey animals (or dangerous predators, for that matter) is a huge advantage for the group, and your friends can assist you with getting ripe berries.

The other advantage is the ability to function in low-light conditions where everyone loses their color vision. Color blind people do not lose the visual cues in twilight. Colorblindness is much more prevalent in norther Europe, which has very long twilight, than it is than Africa and India.

I have often wondered why human colour vision is not evenly distributed across the spectrum of visible light.

Daniell Dennett (I think?) had a good explanation of this:

Q: Why is the sky blue? A: Because leaves are green and berries are red

That is: our colour perception evolved in a particular environment and is optimised towards doing well in that environment by contrasting things that we care about (in that environment).

There is an alternative hypothesis. That it's just an evolutionary accident. Possibly it's a side effect of some other factor that is significant.

I mean, we get a lot of evolutionary traits because of bias through natural selection. But there's probably not much reason to lose a trait if there's no selection pressure to. It still may happen,of course. It's possible we'll all have brown eyes some time down the road. But it's not obviously because of natural selection.

Of course, there may be no strong selection pressure against it. But the odd bias for red-green distinction has been there from the earliest primates, suggesting there is a strong selection pressure in favour of specialising in red-green hue distinction. This then goes directly against having no ability to distinguish so many green and red hues.

Well, unless the only genetic way to maintain this bias includes a risk of colour-blindness, but I kinda doubt that.

Tangent: actually, eye colour is very strongly influenced by natural selection. Specifically, IIRC it's one of the prime examples of social and/or sexual selection pressure being stronger than other pressures, precisely because it has no other survival advantage/disadvantage associated with it otherwise. Since social success is essential for individual survival in our species, being discriminated against for ethnicity in general is a selection pressure (and before I am misunderstood: evolution is an amoral context-optimiser and Social Darwinism is one of the worst perversions of a scientific theory ever).

> Tangent: eye color is very strongly influenced by natural selection...

Maybe, but then what’s your explanation for the prevalence of brown eyes due to natural selection?

Do you realise that you are implying that sexual selection is in favour of light eyes in general? This was not what I stated.

I merely talked about differentiating in- and out-groups, which is localised, meaning the homogeneity of an eye colour within an ethnicity can be explained through sexual selection.

Regarding the prevalence of brown eyes, light eyes and hair are a recent and recessive mutation. That is all that is required to explain why it is localised and less common: it is limited to people who descended from the point of origin of the mutation. In this case that would be Northern Europe.

http://learn.genetics.utah.edu/content/basics/patterns/

i think the social species and specialization both plays a role, but we also have gender specialization. colorblindness effects 8% of men, but only .5% of women. maybe the men have less pressure to select ripe fruit / see social cues. i understand this is because of the x/y chromosome effect, but maybe since it barely effects women its not a strong enough evolutionary pressure to wipe colorblindness out completely.

> i understand this is because of the x/y chromosome effect, but maybe since it barely effects women its not a strong enough evolutionary pressure to wipe colorblindness out completely.

That is a fair point. A slightly less friendly interpretation of this would be that men are the expendable gender, genetically speaking.

> maybe the men have less pressure to select ripe fruit / see social cues

I don't think any gender escapes the necessity to read social cues. There might be differences in which one though, but we're veering into a political minefield of nature/nurture questions here.

For example: there is a famous experiment where people were asked to guess if greyscale pictures of faces (cropped to not show hair) were male or female. The twist was that each face appeared twice, with the only difference in being how high the contrast was (especially the lips, IIRC).

High-contrast faces were more likely to be judged feminine than low-contrast faces. Again, this says nothing about whether this gender perception was nature or nurture.

>I have often wondered why human colour vision is not evenly distributed across the spectrum of visible light.

Instances of color-blindness is different between men and women. One reason hypothesized why women have lower incidence, is spotting infection and discoloration in infants.

Ehm, that is simply a consequence of the Y chromosome missing the genes for color vision, no? Or are you saying that this might be why those genes "fell off the cart" in the evolution of the Y chromosome?

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