There was an interesting article in Der Spiegel a little while back, about the rise of secularism and the study of what non-believers do/don't believe in. Secularists, according to the article, make up around 15 percent of the global population (about a billion people). The source for the 15% figure was adherents.com.
Obviously, any figures about rival belief systems and their popularity come with a massive health warning. Playing God's advocate for a moment, the figures show that a lot of the non-believers come from China. Although the Chinese Communist Party has officially implemented a 'free religious belief policy', the CPC is an atheist body that has historically been hostile to religion and, as far as I know, still maintains that religious belief is incompatible with party membership.Under those circumstances, it's safe to assume that some of China's avowed non-believers came to secularism under duress.
Having said that, the most successful religions have had hundreds of years in which to exterminate rival faiths or intimidate their followers, indoctrinate children too young to think for themselves ('give me a child until the age of seven'), threaten apostates, appeal to tribal/caste loyalty, apply guilt and moral blackmail and enforce respect for the clergy and their interests with authoritarian sanctions. This has only changed relatively recently in liberal, more or less secular, states where clergy are now limited to using soft power, in the form of religious education or subtle social pressures like guilt and harnessing the desire to conform.
More conservative Islamist states, however, still retain old-time religion's historical prerogative of coercive power, ranging from fines and ostracism to physical threats against people of rival faiths, non-believers and apostates.
In short, I'll see your hundred million-odd Chinese who might have been pressured into atheism and raise you as many Pakistanis and Iranians who'd be ill-advised to big up any doubts they have about Islam, not to mention the millions of folk who are Christians or Muslims only because these imperial religions spent a lot of time and effort crushing whatever local belief systems they encountered in conquered lands.
Anyway, even taken with such a large pinch of salt, the figures are interesting in themselves. The main thing that strikes me is that, in global terms, playing belief systems is a winner-takes-all game. I knew that Christianity and Islam were the world's largest religions, but the degree of their relative dominance surprised me. The figures stack up like supermarket market share data, with a handful of massive oligopolies dominating and the smaller players being left to scrabble around for crumbs.
If the world's belief systems were UK supermarkets,* Christianity would be Tesco, the massive steroid-pumped market leader, with Islam coming in second, like a slightly more successful version of either Asda or Sainsburys (which ever one is in second place these days). At around the 15% level, Secularism and Hinduism come in nearer to where Asda/Sainsburys have actually been in terms of market share.
Once you're down below Hinduism, the market share figures drop off a cliff. Buddhism and Chinese traditional religion combined come in at around 12% (slightly more market share than Morrisons). Then you've got "primal-indigenous / diasporic" at give or take 6% - this would be bigger than Waitrose's 3.9% market share if "primal-indigenous/diasporic" was one belief system, but, of course, it's split into hundreds of local traditions
The columns of the Big Few tower over the tiny right hand column of "Other" belief systems which includes what I'd previously thought of as relatively "big name" religions (Sikhism 0.36% and Judaism 0.22%), along with a surprisingly large number of Spiritists, a less surprisingly large number of Juche-sts,** plus assorted Baha'is, Zoroastrians, Jains, Shintoists, and so on.
It doesn't surprise me that secularism has less of a voice than the other big belief systems. Although the studies quoted in Der Spiegel suggest that many secularists broadly share certain characteristics and attitudes, they're not united by any doctrine other than rejecting assertions that come without evidence, however often or loudly such assertions are made. With no unifying dogma or programme other than not privileging unprovable assertions above any other point of view,*** they're never going to present the same united front as an on-message corporatist religion with everybody quoting from the same holy mission statement.
What does surprise me is how much overwhelmingly successful winners of the belief system game, like Christianity with its billions of followers, fear what they're apocalyptically calling "the unrelenting march of secularism". Given the immense tracts of humanity's mental space they've successfully colonised, this looks less like the fear of the marginal and oppressed than the paranoia of a once-potent tyrant whose grip on absolute power is slowly slipping.
* I know the figures are out of date, but they'll do for what's only a rough comparison.
**Less surprising, because I imagine that the N. Korean alternatives to Juche tend to involve labour camps or a bullet in the back of the head, (assuming the basket-case regime can still spare the bullets).
***Individual secularists may have very strong views on particular issues, but with the term "secularist" embracing people as diverse as Bertrand Russell, Billy Connolly, Barry Manilow, Ayn Rand, Frank Zappa, Freidrich Neitzsche, Katharine Hepburn and Warren Buffet, I don't think we can assume there is one rigid ideology to bind them all. Hat tip to My Daily Trek for finding the diverse list of the ungodly and thanks, too, for feeling so sorry for we benighted infidels. I'll be giving your expression of pity pride of place on the mantelpiece, right next to the chocolate teapot.