Assuming we agree the theory of mind applies to monkeys and apes, what could prevent us from thinking that, much like our early human ancestors, they too lend significance to external phenomena they have no control over? Thunder, fire, the moon, the sun, waterfalls can stir awe, wonder or fear in humans. Why couldn't the same natural phenomena stir similar emotions in animals?
In "J.T., JR, The Biography of an African Monkey" (1928), Delia J. Akeley, first wife of the famous taxidermist Carl Akeley, recounts her life with J.T. the female vervet monkey she adopted and whom she studied. She writes: "While the porters were busy cutting down the undergrowth to clear a site for the tents, I gathered an armful of flowers and maidenhair ferns. I was arranging them in a paraffin tin (my safari vase) when J.T., who was tied to the limb of a tree, attracted my attention by her excited manner and peculiar cries. In an effort to learn the cause of her agitation I climbed up beside her. To my dying day I shall not forget the remarkable sight that rewarded my climb. Scattered over the great roof, singly and in groups, were assembled hundreds of monkeys. With arms raised above their heads they sat like statues, facing the setting sun. Everyone in camp, even the porters who were hurrying to finish their task before dark, climbed into the trees to view the monkey assembly. We had not been watching long when an indescribable medley of sounds rose on the air and echoed through the forest. The animal world, led by a mighty monkey chorus, was voicing a hymn to the setting sun. Although I did not see chimpanzees among the distinguished gathering in the treetops, their piercing screams rose shrilly above the trumpeting of elephants and the babel of strange calls and cries that resounded on all sides. Almost as suddenly as the animal ritual began, it ended."
She goes on to explain that she does not think monkeys are sun worshipers but believed they may raise their arms to dry their armpits. This, she said, solved the riddle to her satisfaction.
In Egypt, baboons were worshiped because large troops were regularly seen greeting the sun with vocalization. (For more details, refer to one of my previous posts on Hamadryas baboons).
Other reports mention baboons gathering on rocks in South Africa, looking at the ocean in total silence.
Jane Goodall reports witnessing displays of chimpanzees during thunderstorms over a waterfall - as if they were trying to make sense of it all and maybe try to stop it.
How did spirituality become part of human life? How did it evolve into religion?
I am certainly not qualified to answer these questions, but learning about non human primates makes me wonder.