If you happen to know about evolutionary peaks, good. If not I will briefly try to explain it though it is best if you know about evolutionary theory.
An evolutionary peak is a possible genome in the vicinity of which there is no other more fit genome. All mutations that could happen would result in a less fit genome (i.e. genes that replicate less than the genes in the peak genome). If evolution reaches a peak, it will stay there as it does not ‘have foresight’ (or ‘sight’) to move down the hill to another and higher peak even if there is one relatively nearby. Evolution is blind. The genome is evolutionary stable once at the hill. This continues until a change in the environment happens and another genome becomes more fit. Then evolution continues to change the genome to whatever is more fit. It is rare that a mutation occurs and thus gives evolution an opportunity to evolve change the genome into a more fit one. Evolution takes lots of time. It is even more rare that multiple mutations arise at a time.
Consider now webs of belief. A person’s web of belief is the entirety of all his beliefs. A web of belief may be more justified/warranted/better than another web of belief for a number of reasons (simplicity, coherency, lack of contradictions, mutual support, etc.). A person may change (at will but not completely free at will) his web of belief by changing its parts, either one belief at a time or many beliefs at a time. It is rare that a person changes his belief, if it is in the middle of his web of belief (=connected with many other beliefs). It is even more rarely that a person changes a lot of beliefs at one time.
The analogy is this:
|Part of evolution||Part of web of belief|
|Genome||Web of belief|
|Fitness||Justifiedness, warrantedness, goodness|
|Mutation||Change in belief|
|Evolutionary peak||The web of belief that is more justified than all other nearby webs of belief|
Do you see the analogy? It is quite interesting I think. Similarly to evolution not having ‘foresight’/'sight’, most people do not have the necessary foresight/sight to see that another web of belief although a bit away from their current web of belief is better than their current one. And if they are at a peak or close to a peak, they will not move towards a higher peak if it is a bit away and they only change a few belief at a time. In a way it is rational to change one’s web of belief toward the nearest peak one can spot. Though ultimately it is more rational to try to spot the highest peak and then move towards it. But it is so hard to spot the highest peak (=discover which web of beliefs is the best), that we for all practical purposes cannot do so and thus stay near a local web of belief. Further, it is not humanly possible to discover with a high degree of certainty which webs of belief are the peaks and which are not. There is no known formula in which one can input all one’s beliefs (there are too many of them too) and in the output is the web of belief’s goodness rating.
But if we cannot do this with much certainty, how should we be able to say that another person has a worse web of belief than we have with much certainty? We cannot. Though we can do rough analyses and make somewhat justified claims about other people’s webs of belief. It is vary hard if not impossible for two rational and sophisticated people to discover which of them has the best web of belief. If their webs of belief are very different and are both near a local peak, then there is no way for one of them to move towards the other while continuously getting a better web of belief. He would need to change many/a lot of beliefs at once, and this very rarely happens. Arguments usually only change a single/small number of belief(s) in a person at a time. What would need to be done to change one’s web of belief so drastically, rationally, is an evaluation of all relevant arguments ‘viewed’ from both webs of belief. In the case of atheism/theism, doing so will take at least several years. It would be much better if one simply found oneself closer to the atheism peak to begin with (I did), or changed to moving toward the atheism peak without first moving towards the theism peak. But then, a person who happened to be a theist (because of, say, his parents) would most probably first move towards the theist peak than the atheist peak. That is the most rational way given a conservative principle like “change as little beliefs at a time as possible to continue gaining a better web of belief.”.
Still, given the above, I’m relatively sure that, say, a thomist (in fact it was a thomist that inspired me to write this essay) has a worse web of belief than I do and that the highest thomism peak is much lower than the highest atheism peak. But I should not claim much certainty about this.