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Don't we have single celled organisms with more than one 'eye' now? We've been able to sense light and shadow even before we became multicellular, didn't we? And this article seems to be implying rather otherwise.
What benefit is an eye unless there is also the capability of processing and using the information? How would both evolve simultaneously?
And note that box jellyfish have 24 eyes, some of them highly complex, but no brain. You can look into their behavior to find out what they do with the information.
Darwin was not puzzled. “To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree. When it was first said that the sun stood still and the world turned round, the co…
I think Darwin might be, despite everything, underrated. I wish more people had this level of both intellectual and emotional strength and honesty.
Gift link: https://www.nytimes.com/2026/02/23/science/evolution-vertebr...
https://www.cell.com/current-biology/fulltext/S0960-9822(25)...?
What benefit is an eye unless there is also the capability of processing and using the information? How would both evolve simultaneously?
A photosensitive patch of cells could be wired directly to motor cells/muscles on the opposite side, which would allow the organism to swim toward the light (maybe useful for feeding or migrating, etc.)
Earlier quoted context omitted.
A photosensitive patch of cells could be wired directly to motor cells/muscles on the opposite side, which would allow the organism to swim toward the light (maybe useful for feeding or migrating, etc.)
How would the photosensitivity and wiring to muscles come about at the same time?
Each piece, light-sensitive proteins, cell-to-cell signaling, contractile cells, evolved independently and for other reasons long before being co-opted into anything resembling vision. The question "how could A and B arise simultaneously?" dissolves once neither A nor B was new.
my question has always been why (I think most vertebrates) stop at two? It seems that an extra eye here and there could be really helpful. Maybe it's because all verterbrates evolved from an ancestor that had two eyes, and once the template is in place, it was simply too deep a local maximum to evolve out of? Similar to the 5-digit hand design that all vertebrates share.
Spiders have 8 eyes. As with vertebrates, this number doesn't change, but there is variation in what it means.
A "normal" spider doesn't really use its eyes. It just has them.
Some spiders are different and rely on their vision. Those spiders have two primary eyes, which they rely on, and six secondary ones, which they don't.
Moving to insects, they often have compound eyes. Two compound eyes. A mantis has two primary compound eyes and three secondary non-compound eyes.
All this convergence suggests to me that even if you have the option to grow more eyes, the correct number is two.