You know Darwin's theory of evolution? I've been thinking about this recently, and have found that the principles of this theory, with little modification, can apply to ideology as well:

Darwin's original theory of evolution, as dissected by Ernst Mayr, is quoted here:
OBSERVATION 1: All species have such great potential fertility that their population size would increase exponentially if all individuals that are born reproduced successfully.
OBSERVATION 2: Populations tend to remain stable in size, except for seasonal fluctuations.
OBSERVATION 3: Environmental resources are limited.
INFERENCE 1: Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of offspring surviving each generation.
OBSERVATION 4: Individuals of a population vary extensively in their characteristics; no two individuals are exactly alike.
OBSERVATION 5: Much of this variation is heritable.
INFERENCE 2: Survival in the struggle for existence is not random, but depends in part on the hereditary constitution of the individuals. Those individuals whose inherited traits best fit them to their environment are likely to leave more offspring than less fit individuals.
INFERENCE 3: This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over the generations.

Now, let's change the wording slightly to apply to ideology. "Survival" is an idea's ability to be believed, and an idea "reproduces" when another person begins to believe it:
OBSERVATION 1: All ideas have such great potential acceptance that their number of people who believed them would increase exponentially if the idea was accepted without question.
OBSERVATION 2: Only a percentage of the human population buys into a particular idea.
OBSERVATION 3: Some ideas contradict: accepting one idea means rejecting another.
INFERENCE 1: Production of more ideas than the environment can support leads to a struggle for credence among different ideas, with only a fraction of ideas being accepted.
OBSERVATION 4: Ideas vary extensively in their characteristics; no two ideas are exactly alike.
OBSERVATION 5: Much of this variation springs from derivative ideas.
INFERENCE 2: Survival in the struggle for acceptance is not random, but depends in part on the constitution of the idea. Those ideas whose traits best fit them to their audience are likely to take better hold than less fit ideas.
INFERENCE 3: This unequal ability of acceptance will lead to a gradual change in our ideology, with favorable ideas accumulating over the generations.

This idea has other implications as well: Classes of ideas (species) can die out, ideas can "interbreed", ideas can die out but still be known (fossils), etc. Tell me what you think about this.

Observation one for your metaphor on ideology seems unsupported.

How did you arrive by that observation?

Good point.

And I suppose even if ideas were accepted at a linear rate, not exponential, it wouldn't have much bearing on the argument.