I often hear people speak of democracy as the next, or the final, inevitable stage of human social development.  Its inevitability is usually justified not by describing power relations that result in democracy being a stable attractor, but in terms of morality - democracy is more "enlightened".  I don't see any inevitability to it - China and the Soviet Union manage(d) to maintain large, technologically-advanced nations for a long time without it - but suppose, for the sake of argument, that democracy is the inevitable next stage of human progress.

The May 18 2012 issue of Science has an article on p. 844, "Ancestral hierarchy and conflict", by Christopher Boehm, which, among other things, describes the changes over time of equality among male hominids.  If we add its timeline to recent human history, then here is the history of democracy over time in the evolutionary line leading to humans:

1. Pre-human male hominids, we infer from observing bonobos and chimpanzees, were dominated by one alpha male per group, who got the best food and most of the females.
2. Then, in the human lineage, hunter-gatherers developed larger social groups, and the ability to form stronger coalitions against the alpha; and they became more egalitarian.
3. Then, human social groups even became larger, and it became possible for a central alpha-male chieftain to control a large area; and the groups became less egalitarian.
4. Then, they became even larger, so that they were too large for a central authority to administer efficiently; and decentralized market-based methods of production led to democracy.  (Or so goes one story.)

There are two points to observe in this data:

• There is no linear relationship between social complexity, and equality.  Steadily-increasing social complexity lead to more equality, then less, then more.
• Enlightenment has nothing to do with it - if any theory makes sense, it is that social equality tunes itself to the level that provides maximal social competitive fitness.  Even if we agree that democracy is the most-enlightened political system, this realization says nothing about what the future holds.

I do believe "progress" is a meaningful term.  But there isn't some cosmic niceness built into the universe that makes everything improve monotonically along every dimension at once.