Here's an interesting video about evolution.
(via Daniel Fincke)
To me, it's more interesting in what it says about evolution than as a rebuttal to Paley's argument against evolution. What I really get from this video is that major changes appear to be abrupt, not gradual. We see the "pendulum era" for hundreds of generations, and then in only a few generations we get the "single-handed clock era"; the pendulums almost completely die out. It's an important illustration of one mechanism of punctuated equilibrium. There are, of course, other mechanisms in the much more complicated and varied world of both biological and social evolution, but the model is interesting nonetheless.
While punctuated equilibrium in biological evolution seems strongly (but not exclusively) associated with allopatric speciation, the idea of some internal more-or-less "abrupt" transitions (in "geological" time) seems more pronounced in social evolution, and the mechanism from the video (the accumulation of neutral variation) also seems to have special application to social evolution.
Basically, there's a lot of neutral variation in our ideas. People think up new ideas (or variations on old ideas), and they more-or-less float around the population with no positive or negative selective effect. There are a lot of people, so sooner or later some fortuitous combination of neutral variations comes together into an "ideology" that really takes off; its prevalence now indirectly exerts a negative selective effect on the old dominant ideology.
Which is why, I think, I don't worry too much about numbers, both of atheists or communists. I don't know that either atheism or communism (or, more precisely, some ideology that includes atheism and/or communism) will actually dominate human society, but if it does, it will probably do so very abruptly. Thus I'm not too worried about my recent commenter's boast that atheism is on the decline, and not just because any statistics coming from the religious are probably outright lies. There isn't really anything at all we can infer from day-to-day or even year-to-year numbers; social evolution happens on a generational time scale.
Furthermore, evolution happens only when there's real negative selection pressure against some ideology. In the clock model, the selection pressure is a constant and fairly simple part of the experiment; in social evolution, selection pressure is considerably more complex and non-obvious. Therefore, one of the prerequisites for the growth of both atheism and communism is the removal of direct negative selection pressure for these ideas. Atheist activists have been especially successful — as have racial, gay and women's rights activists — at eliminating this selection pressure. More work in all these areas still remains, of course, but reducing and eliminating simple selection pressure (it is much less intrinsically shameful today than a generation ago to be an atheist, woman, gay, or a racial minority) is an essential first step.