[a-priori]

You're right that religion seems to be a human universal. I believe that every human population ever studied practices it in some form or another.

But, what may be declining is not religion per se, but rather monotheism. Zoroastrianism, one of the first monotheistic religions, emerged only in the 2nd century BCE. For the entirety of human history before that, about 200 millennia, humans practiced some form of nature worship, ancestor worship or polytheism.

It may be that the age of monotheism is coming to an end, but what comes next is anyone's guess.

[phamilton]

2nd Century BC? What about the Jews? While exact dates are not very well known, Jerusalem was invaded around 600 BC. The dead sea scrolls have been dated back to well before the 2nd Century BC.

[a-priori]

You're right, my mistake. I had it in my head that Zoroastrianism was first, then looked up its origins to get a date, but didn't double-check it. It looks like Judaism pre-dates Zoroastrianism by a couple centuries, and Atenism (emerging in the 14th century BC) preceded both.

The argument still stands. We're still talking about 4 millennia of monotheism, preceded by 200 millennia of various other forms of religion.