> We know that but would a Neolithic person know that babies are curled in the womb? Babies don't come out curled up.
All it would take for the Neolithics to find out for sure would be to cut open a pregnant woman. A ghastly experiment for sure, but not beyond the powers of Neolithic mankind to dream up.
Even easier would be to observe the growing foetus as it develops in its mother's womb: after a few months the position of the head, the legs, the arms become pretty evident -- as anybody who has had a pregnant wife will know.
I suspect Neolithic cultures were far more self-aware than our modern cultures would give them credit for.
And they did this enough that an entire culture was influenced to bury their dead that way for thousands of years?
Doubtful.
More likely is that people tend to sleep curled up and that was what influenced it.