https://en.wikipedia.org/wiki/Dolmen

I understand very little is known about dolmens at all, but are there any theories out there amongst historians about how/why this same basic structure popped up all across such a huge part of the world? Would it make sense to assume that they are all the product of a single culture that managed to spread right across the three continents at some point in prehistory?

(I posted this same question a few months ago but didn't get any replies, so I just wanted to try once more.)