In some cultures, swear words are drawn mainly from sex and bodily functions, whereas in others, they're drawn mainly from the domain of religion.

In fact, the book shows that language is in a rough state of equilibrium: some words disappear and some structures are eroded, but new ones are created at the same time, and these do the job just as well as the old ones, ... It is true, of course, that decay is one prominent force in the course of language evolution. But there are also forces of creation and generation operating at the same time.

and people believed that swearing falsely by a god would bring the terrible wrath of that god upon them.

This is a very tricky question, because ultimately no one knows where the original homeland of the Indo-Europeans was, and when they started spreading into Europe and Asia,

So if you, O subsequent ones, ever deign to look down at us from your summit of effortless superiority, remember that you have only scaled it on the back of our efforts. For it is thankless to grope in the dark and tempting to rest until the light of understanding shines upon us. But if we are led into this temptation, your kingdom will never come.

The Moral is that gardeners pine, Whene'er no pods adorn the vine. Of all sad words experience gleans, The saddest are: "It might have beans." (The did not make this up myself: 'Twas in a book upon my shelf. It's witty, but I don't deny It's rather Whittier than I.)