How Much of the Reality of the World Can Be Explained by Nature?

To be a human being in our modern world, you always have to be immersed within a particular culture. But what is a culture other than an elaborate collection of norms and taboos that we abide by? We can easily look to different cultures around the world presently, and all throughout human history,. To see that a culture can function and flourish when things are completely different. So it makes grampsy wonder, to what extent is the current set of cultural norms serving to reinforce itself?