Why do eyes blink in unison? (Details)

Because our vision is lined up in such a way that we only see correctly with both eyes, unless we turn our heads slightly. If we blinked one eye at a time, everything would appear to jump back and forth.

That’s a good question. It’s true we are for a moment vulnerable when we blink (and sleep for that matter) but a blink is quick, and if you only close one eye every 4 seconds your view would constantly shift left and then right. You would have trouble walking, driving, reaching out for a hug, it just wouldn’t work well.

I’ll guess it takes fewer brain cells to blink both rather than have the ability to blink independently. Maybe that additional circuitry cost more than that ability was worth.
Humans now move at speeds much greater than they did historically. We drive, fly planes, fly in planes. A blink, ¼ second, can make a difference. How many times have we been driving, started to sneeze and both eyes closed? How many accidents does that cause?
For that reason you cannot be a fighter pilot if you sneeze when suddenly exposed to the sun.

Perhaps because our vision is set up in a more predatory fashion than at the sides like prey animals? Do deer and such blink in unison?

^I’ve worked with deer before, I think they blink in unison as well… Like I said, I couldn’t think of an animal, capable of blinking, that doesn’t blink both eyes together.

Chameleons’ eyes move independent of each other, but I don’t think they blink differently…

Well otherwise we’d be frequent winkers & everyone would feel they were been flirted with.
Ewwww, imagine though, would be like you were the only woman on board a navy boat during the war.

^I know that you’re kidding, but maybe you’re onto something. Maybe it’s a body language thing…

No. If our eyes blinked independantly, winking would never have become a thing.

Well. A wink, is different from a blink…