r/evolution • u/UselessCommon • 1d ago
question How did sleep evolve in almost all land animals?
Sleep, or at least the very common form of it where sleep involves being almost entirely unaware and defenseless at nearly regular periods, appears to be a completely devastating disadvantage. I get that there presumably are overall performance gains from such a total rest, and I get that operating at night is less calorically efficient due to a greater need to warm the body, but it baffles me that predators that did not need to sleep did not hunt everything that needed to sleep like that into extinction. It does not matter how much smarter and faster and stronger you are if you are caught sleeping, with all those capabilities out of the picture, and promptly eaten. Why does being somewhat more efficient at performing tasks outweigh automatically losing any fight a third of the time, at exploitable regularly scheduled periods?
It is especially baffling since, say, dolphins, descendants of land mammals, evolved to functionally never sleep and function just fine as they are - they have half of their brain rest at all times, and appear plenty capable with just the other half of it. That this path was possible but so very rarely taken implies that this isnt the case of a locked-in quirk from some ancient common ancestor (like ie eye blind spots are), but that regular nearly-defenseless sleep is a systematic advantage on land. How?
I understand that animals like moles and squirrels can just recuperate in very small, hidden and secure places, and that for very herding animals it is okay to lose some members of their herd to predators if the rest can wake up and reliably defeat the predators (even then, its also baffling that some kind of a rotating-keep-watch instinctual behavior pattern isnt common). I do not understand it being nearly-ubiquitous, not at all.
