Sorry to jump in half way and mostly uninformed, but maybe that's an early form of sky burial? Burial by carrion birds is still practiced today.
(a) is such a belief really compatible with what we think is the selective force of evolution, i.e. stay alive long enough to make sure your children have children? In other words, is this something people truly feel when it comes down to it, or is it just a story they tell each other in low-stakes situations? and
(b) even if I believed in this, that's orthogonal to my belief that every human has a valuable role to play in this, current-life society!
Your argument about selective pressure would by the same logic lead one to conclude chaste nuns can't exist and monestaries and vows of celebacy are fiction.
Religious belief just needs to be useful on average for there to be selective pressure.
Also evolutionary psychologists can't really explain the existence of gay people (attempts to do so have been a stretch, according to the evolutionary psychiatrist author of The Moral Animal) which demonstrates the limits of declaring things are impossible due to thought experiments about evolutionary pressure.
The Aztecs sacrificed an estimated tens of thousands of people a year, because they believed it would postpone the next apocalypse in which everyone would die
incentives drives us
overpopulation was controlled by sacrifice and infanticide
Through virtually all of history, there's a strong correlation between "more people" and "better living conditions".
We are a social species. We're practically made to effectively make use of as many of us as possible to preserve ourselves.
That's survivorship bias. Populations always try to grow, not to shrink. However, growth will only occur when possible (due new technologies or more resources being available).
The last agricultural famine in England was only in the 17th century.
“Another unnerving oddity is the curious number of carvings which show people with six fingers. Is this symbolic, or an actual deformity? Perhaps the mark of a strange tribe? Again, there are more questions than answers. Crucially, however, we do now have tentative hints as to the actual religion of these people.
In Gobekli Tepe several skulls have been recovered. They are deliberately defleshed, and carefully pierced with holes so they could – supposedly – be hung and displayed.
Skull cults are not unknown in ancient Anatolia. If there was such a cult in the Tas Tepeler it might explain the graven vultures pictured ‘playing’ with human heads. As to how the skulls were obtained, they might have come from conflict (though there is no evidence of this yet), it is quite possible the skulls were obtained via human sacrifice. At a nearby, slightly younger site, the Skull Building of Cayonu, we know of altars drenched with human blood, probably from gory sacrifice.”