Why do we blink both eyes at the same time rather than winking each eye as needed?

Why would winking independently be better?

The benefit would be a minor improvement whereby a person would receive continuous sight of the area of vision shared by both eyes. I'd also assume that it would be more likely for the wink-as-needed mechanism to evolve than the blink-as-needed mechanism were there no benefit to blinking over winking.

Why then has evolution favoured blinking?

My guess at why is that the overhead on our brain of switching between binocular vision to monocular vision is more significant than the overhead of momentarily pausing our visual processing.

I also believe that some animals don't blink, but wink; e.g. chameleons. This supports my theory as their eyes operate independently, so their brains would have to cope with the variance in each eye's information anyway. That said, their wink is different; i.e. they roll their eye inside their head, rather than having an eyelid.

Research so far

I found a couple of Reddit posts:


1 Answer 1


Looking at it completely in terms of evolutionary pressure:

1.1 The whole idea of binocular vision for humans, (and some other species) is depth perception. If you suggest continuous, alternate winking, the cognition of the individual would be seriously affected. The 'wink as needed' mechanism (assuming all other visual processes are as they have evolved today) would be like continuously alternating between a pair of binoculars and a telescope while still trying to move forward.

1.2 If you are suggesting that there would still be an evolutionary pressure for winking, then its very likely that the evolutionary pressure for coordinated motion/ efficient cognition acting together with the evolutionary pressure for depth perception would be much higher as compared to it. (This would especially be true if eye-brain coordination evolved before the blinking mechanism, as is seen to be the case, which explains your point on 'how we are rather than how we got here'. Obviously fish have evolved some eye-brain coordination, but don't blink)

This link explains evolutionary pressure for depth perception/stereopsis to an extent https://en.wikipedia.org/wiki/Depth_perception#Survival

2.1 As for the chameleon, the winking/ eye rolling mechanism might be very closely linked to the evolution of chameleon vision. It is seen as the link for studying evolution of binocular vision and stereopsis(depth perception) from monocular vision.



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