Bering's main thesis is the "theory of mind" - the trait that, among all species, humans alone possess. The theory depends on our evolved ability to:
1. Mind-read - to predict what others are thinking and what they're likely to do. 2. Participate in and dissect gossip (the most widespread hobby humans have). 3. Learn to co-operate or be ostracized by the group. 4. Contemplate our own mortality.
These evolved abilities were responsible for the cohesiveness of early humans and their ability to survive. Bering says a by-product was the "instinct" to believe in supernatural agents.
The theory is not his own but Bering makes good use of it in applying it to belief in gods. He says, "Theory of mind is as much a peculiar trademark of our species as is walking upright on two legs, learning a language, and raising offspring into their teens."
Aside: I might add, from personal experience, this last project can extend into the twenties or later.
Thing is, religion is not the major emphasis: the theory of mind is and it evolved simultaneously with language and religion. Commitment to religion - at least in the early evolution of humanity - wasn't even costly. It was a by-product and proved helpful in enforcing social compliance. It was part of the package.
As Bering writes about the evolution of the mind, he develops the idea of a "Belief Instinct." Many atheists believe that "religious ideas amount to a sort of cultural virus, the human brain being parasitized by virulent concepts that children catch like a bug from infected adults." Not so, says Bering: "Just like a crude language sprouting up, at least some form of religious belief and behavior would probably appear spontaneously on a desert island untouched by cultural transmission, particularly beliefs involving purposes and origins." Then he says, "....since natural selection works without recourse to intelligent forethought, this mental apparatus of ours evolved to think about God without need of the latter's consultation, let alone His being real."
Bering says all this without sounding derogatory about any particular belief system - he doesn't try to talk anyone out of their religion. As to an afterlife - when you die your kidneys die, as does your heart, your liver, your spleen, and yes, your brain. Since your mind is what your brain produces, it's gone too, along with that 21 contested grams of soul. Like Occam said, the simplest answer is likely to be correct. Like Ecclesiastes says, the solution to life is to enjoy it while you can while doing all the good you can because it will soon be over. And that's all there is.
Our mind, our identity, is something the brain has provided for us. It is able to perceive for us our mortality - an apparent unique condition only we possess within the animal and plant kingdoms. It's not particularly comforting that our mind dies with our bodies. Like religious people, I, too would like it to be different, but there is no scientific evidence to justify any other conclusion. This scenario is unacceptable enough to guarantee the invention and persistence of belief systems that offer more pleasant alternatives. I would not deny that comfort to anyone despite overwhelming evidence for the sad truth. Our parts may be (and are) broken up and used by nature elsewhere but our minds will die. No wonder we invented gods.