Savannah: We owe our vision to bacteria. Specifically, the bacteria that gave early vertebrates a gene we need for how our vision works - over 500 million years ago.

This gene makes interphotoreceptor retinoid-binding protein, or IRBP. And IRBP is a part of the retinoid cycle, a process unique to vertebrate eyesight.

See, when light triggers the photoreceptors in our eyes, it causes a certain signaling compound to change shape, which turns the light into electrical signals that go to our brains. And IRBP is what helps those compounds change back into their original shape, so the process can happen all over again.

And early vertebrates probably got the gene for this protein directly from bacteria through a process called "horizontal gene transfer." In bacteria, the gene made an enzyme, but after those vertebrates grabbed the gene, it mutated to produce our IRBP protein. And the rest is history.

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