The bit of atheist apologetics I enjoy the least, and find the most absurd, is the evolutionary explanation for religion. Daniel Dennett wrote a whole book on it, and Michael Shermer has written several. The point is generally that religion developed because it, or the bahavioural basis behind it, has survival value.
Shermer says our ability to attribute intention to things that have none (like the sky) is a by-product of our ability to predict the behaviour of predators. Dennett says that religion builds social cohesion in small hunter-gatherer groups and hence helps them to survive by working together. EO Wilson says altruism grows out of our drive to care for our offspring and hence ensure our genetic continuity.
The thing about all these explanations is that they seem plausible, and could even possibly be true, but the evidence for them is almost non-existent. This is because the science of evolutionary biology has few mechanism for gathering evidence about past behaviour and even fewer for the thoughts of pre-literate humans. We can tell what animals looked like, what sort of habitats they lived in, and even what they ate, from the physical remains in the fossil records. However when it comes to how they behaved, and why, we're mostly just guessing.
These explanations are in fact part of a wider art-form. This art is not really practiced by serious scientists in the course of their research work. "We don't know" is one of the most important phrases in the research scientists' lexicon. It's what drives them to go and find out, and what keeps them humble about the reach of their craft. Research papers are couched in qualifications and limitations, written in a careful, circumspect style which ensures the researcher claims not a speck more than the evidence will support.
However, the Art of Evolutionary Explanation is a staple of science journalism. The caution and technical precision of professional research is admirable, but dull and virtually incomprehensible to non-specialists. The science journalist's job is to explain this complex and nuanced science to a lay audience. Science journalists usually have some kind of scientific background and some, like Stephen Jay Gould, for example, or Stephen Hawking, are distinguished scientists in their own right.
Yet when they write for a popular audience they operate under severe constraints. Hawking, for instance, explains that when he was writing A Brief History of Time his editors told him each formula he included would halve his readership. In the end he included only one: e=mc2, which most people think they understand even if they really don't. Yet the science which made him famous is almost entirely mathematical.
In this kind of writing, "we don't know" is a difficult (although not impossible) message to sell. People are reading these books because they want to know, and the temptation to answer the question is too strong to resist. Hence the birth of the Evolutionary Explanation.
We know that life evolved, the evidence for this is overwhelming. However, how a specific life-form evolved, how it got to be like it is and where it is, is often unclear. Our evidence is just too patchy. Scientists say "we don't know". Science journalists, on the other hand, are likely to reach for the nearest hypothesis. Here's an example from A Sheltered Life: The Unexpected History of the Giant Tortoise by Paul Chambers, explaining how giant tortoises came to live on the remote Galapagos Islands.
...sometime between about 5 and 2 million years ago the ancestor (or ancestors) of the Galapagos Tortoises were washed up on a beach, having crossed 1,000 kilometres of open ocean from South America. This ancestor was probably washed up on one of the islands of the south-east of the archipelago....
As Michael Shermer would say, "perhaps". How often do South American land tortoises make it to the Galapagos these days, and if they do how long do they survive and do they manage to set up breeding populations? What, in reality, are the chances of not just one, but a viable breeding population of tortoises (which do not swim) making such a hazardous journey? The more you think about the scenario, the more it stretches credulity. However, since this explanation fits the genetic evidence, and we don't have a better one, it will have to do.
At least Chambers has genetics on his side, even if it falls a fair way short of proving his hypothesis, and he lacks viable alternatives. Much less so with the origins of religion, which is much more widespread and complex than the giant tortoise and is subject to a number of alternative explanations. We certainly know that all peoples everywhere have religions of one sort or another, and that these have some common elements even though they also differ widely. We even have some, albeit patchy, knowledge about how some of these came about. However, it is a long leap from this knowledge to the chains of causality proposed by Shermer, Dennett and Wilson.
What ultimately leads them to their conclusions is much the same kind of reasoning that leads Chambers to his. They feel they know that religion evolved because everything evolved. This is a cornerstone of their worldview. They just need to explain how it happened. Here's a possibility that fits the evolutionary hypothesis. In the absence of other possibilities - like the founders of the religions having special insight or revelation, say - this seems the most likely one.
When you have a hammer everything looks like a nail. If religion did indeed evolve in a way analogous to the evolution of species, then these might be part of the explanation of how it happened. However, until that case is made, our high profile atheists are just guessing.
Perhaps they should take a lesson from one of our most popular science journalists, David Attenborough. I wish I could remember the name of the film to find you a link to it, but at one point in one of his documentaries he shows footage of a species of seabird. When one of the bird couple arrives back at the nest, the pair engages in an elaborate and comical dance which involves bobbing up and down in front of each other and slapping their beaks together. Always the most straight-faced of narrators, Attenborough chortles and says, "I have no idea why they do this."