Last week, in a lecture presented by the Non-religion and Secularity Research Network, Jon Lanman set out to explore the evolutionary origins of atheism. Lanman, who is originally from St Louis, Missouri, recently completed his DPhil in anthropology at Oxford. His thesis explores atheism in the west including both non-theism (a general lack of belief in the existence of supernatural agents) and what he calls "strong atheism", defined as "the moral disapproval of and active stance against such beliefs".

"Is a science of atheism possible?" he asked, noting that there is a "great diversity of atheisms" and refusing to get tangled up in defining the term too closely. For him, the important thing is to ensure that the phenomenon being studied is not viewed as a constellation, which is only a pattern a human perceives while looking at a group of stars from a particular location and angle.

If most explanations of the origins of religion are simplistic – fear of death, an attempt to explain the universe – the same is true of explanations of the origins of atheism. Explanations such as intelligence, rationality, education or rebellion are too pat.

For one thing, there are significant national differences. Non-theists make up 43-80% of the Scandinavian population and 13-44% of the UK, but only 3-9% of the US. Ethnographic data disputes the notion that people turn to religion for comfort in a frightening world.

The most comfortable places – San Francisco, say, or parts of London – tend to have the most comforting religion, stripped of punishment and instead focusing on close, personal relationships with God. Non-comforting ideas can be found all over the world, but mainly in existentially non-comfortable places – Africa, for example – where people care about following rules. In any event, comparing Scandinavia, the UK and the US shows that non-theism can't be simply associated with education or with IQ.

The rationality explanation is countered by behavioural and cognitive literature: humans are good at seeing patterns where they do not exist. Basketball players believe in the "hot hand", the idea that a player who has scored a number of shots in a row should be given the ball because he's "in the zone" and is less likely to miss. This theory can be disproved by statistical analysis, but coaches and players still believe it.

Confirmation bias, for another example, inclines humans to look for confirmation of what they already believe rather than for evidence disproving it.

The conjunction fallacy leads people to believe that multiple conditions are more probable than single ones. Given that I am a sceptic, is it more probable that I am a feminist or that I am both a feminist and an agnostic? Associating scepticism and agnosticism, you're likely to pick the second option; but the probability that I am both a feminist and an agnostic is actually lower than that I'm just a feminist.

Turning to sociology, the literature indicates that threatening environments increase superstitious behaviour and strengthen commitment, communities, and attachment to ideologies. In many places, Lanman said, "religion is often the only game for social insurance".

At the same time, he cited Joe Henrich's work on "credibility-enhancing displays" (Creds). Before we had language we were taught by demonstration.

Once you have language, "you need a bullcrap detector".

That is often watching people's actions: they say they're religious, but do they practise or go to church? More Creds, less scepticism. Here Lanman cited Roger Dudley's study of Seventh Day Adventists that showed a greater likelihood of becoming apostates if during their adolescence their parents were not practising.

So consider those national statistics again: the US has massive inequality and a weak welfare state and a very small percentage of (open) non-theists. In the mid-20th century, Scandinavia built a very strong welfare state and now has a high percentage of non-theists.

Strong atheism, however, is a different matter: "Atheism can also be an identity," he said (just as religious beliefs can serve as markers for social groups), "though I wouldn't call it a religion." As an ideology, strong atheism tends to emerge under the threat of theocracy. Strong atheism found its public voice in the US under the twin stresses of George W Bush's second term in office and 9/11's demonstration of the worst dangers of fundamentalism.

"The UK," Lanman concluded, "seems right in the middle between Scandinavia and the US." The UK had Blair, and has blasphemy laws [see footnote], a growing perception of the dangers of militant Muslims, and increasing numbers of faith schools – "but you don't have Sarah Palin and Mike Huckabee".

• This footnote was appended on 15 April 2011: it should be noted that the blasphemy laws in England and Wales were abolished by the Criminal Justice and Immigration Act 2008.