You're presenting group selection, natural selection at the level of the group, as an established theory. But that's not the case.

From Wikipedia, quoting evolutionary biologist Jerry Coyne: "Group selection isn't widely accepted by evolutionists for several reasons."

https://en.m.wikipedia.org/wiki/Group_selection

>All that's required for a trait to persist is that it benefits the pool.

Or that it's less bad than whatever beneficial trait it's coupled to.

Humans consume a lot of water in order to shed heat. Our backs are pretty f-d up. Our brains waste a lot of energy and require a very long childhood. But on the flip side we're basically terminator compared to the African fauna our primitive ancestors hunted.

I'm assuming you're right since I don't know much about this subject, but how does that mechanically work? How does a trait, even if it is beneficial to the community, get passed down if the members that have that trait don't have offspring?

It could be recessive, so it only gets expressed if an individual has two copies of the recessive gene.