The red and green specialists: why human colour vision is so odd
aeon.co
aeon.co
What a load of bull. Dogs and wolves eyes are facing forward, as do cats', owls', jumping spiders' main eyes, and generally those of most hunting predators. Eyes facing forward is good for depth perception and judging speeds and thus hunting, a bigger field of view is good for detecting threats from any and all directions and thus for prey animals. The location of the eyes depends mainly on where the animals sits on the predator<->prey scale. Apes tend to be apex predators, thus the predator eye location.
A few snippets:
a compound eye, made of thousands of small units that each detects light independently
12 to 16 different photoreceptors in its midband
has six photoreceptors dedicated to...UV
incredibly sophisticated UV detectors
http://www.businessinsider.com/the-mantis-shrimp-color-visio...
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.
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.
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).
Maybe, but then what’s your explanation for the prevalence of brown eyes due to natural selection?
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.
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.
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.
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).
It is not a good idea for your credibility that the first thing you say in an article is blatantly false.
BTW. Wikipedia says that trichromatism was normal for mammals in the past, and then they lost one or two cones, which would suggest a different development path. The article does not touch on this.
Or did distinct cones were reduced, and then one of them split into two again? It's also interesting whether chemical structure of cones is similar. I guess I gotta do some research on my own.
As for genetically engineering an extra cone, they did that with mice, mainly to address the chicken-and-egg question: if you get an extra cone, does the brain learn to see extra colours? It seems like it would[1].
What you propose would be almost impossible to test though. Sure, you can test for distinction quite easily, but measuring the cost/benefit of it in evolutionary terms is a lot harder. There is a trade-off to make here in what perception the eyes and brain are optimised for, perhaps other forms of perception will suffer to the point of it not being worth it.
Also, bad news regarding UV: our cones can perceive it, but our lens filters it out, suggesting it has too many disadvantages. The main reason is likely because UV light creates too much chromatic abberration in a single-lens system, making it hard for us to focus properly[2]. This is not a problem for the kind of vision required by a honey bee, but it would be for humans.
[0] http://science.sciencemag.org/content/343/6169/411
If anyone knows anything like that that's been tried I'd be really interested.
Have you never noticed how colour blind people always complain that so many interfaces use red and green as two opposing colours? Or how those colours are overused in carthography? Because we do.
That's because you just described traffic lights.
Now, I don't think a lot of biological research have been done when deciding the colors of traffic lights, there is research about why they feel so obvious.
The idea is: Red is the most noticeable color, good for signaling danger or requiring attention. Green is distinct from red, it is also the brightest color, so it is good as a complement for red. Yellow is simply the intermediate between red and green.
Boy that's some next level webpage design!
[1] https://aeon.co/ideas/the-red-and-green-specialists-why-huma...