My guess is that when humans came to be the largest “animal” around, the Neanderthals may have taken to catching and eating their sapiens neighbors. We sapiens then proceeded to kill Neanderthals whenever possible except for keeping some of their women.
I’ve heard that the Native Americans engaged in cannibalism, and I know that in Irian Jaya, there were many tribes that were head hunters and practiced cannibalism well into the 20th century.
The book, The Peace Child documents it.
I doubt *globull warming/cooling/climate change* was the factor that *pushed* them into it.
It was their culture.