[ksk]

You are severely misreading what is being said here. "very likely to be of use" is not the same as being provably true. The point being made is that of usefulness and correlation. Those two things are essential to the way humans have and continue to think. In day to day life, nobody does 'studies' to prove every single thing to be true. That is why customs that survive time can sometimes have a grain of truth to them. And what's interesting is that even if they didn't it could be that blindly following something for years has created an evolutionary pressure on the body to adapt.