[The_Colonel]

> It seems like this article just lists a bunch of facts about sloths.

It's because there's no singular reason for it. Evolution is blind (pun not intended), doesn't have motivation or reasoning. I think the article makes a good job explaining the set of evolutionary forces which likely pushed sloths into this direction.

> But doesn’t say why being nearly blind

The article mentions that this mutation already happened to the sloth ancestors, which lived on the ground. It's possible that it provided some advantage to those, or perhaps it didn't actually matter much (perhaps they were nocturnal?)

[Log_out_]

Evolution happily trades everything away that would allow to escape the niche your stuck in. And one day, you are a koala, unable to recognize leaves when they are not on branches, a planktonwhale beaching yourselves, a panda who needs electric help to procreate, or a sloth to slow and calorie low to eat. Moral of the story: High effort Low Energy diets are a evolutionary swamp - never eat all your veggies.