[sorry for the long blog! Complex and sensitive issue]

An apostate is someone who renounces or changes their religion, and is often treated with various forms of punishment, such as shunning, ostracism, violence and even death.

This distressing story makes me think, why would a cultural belief system that so often espouses love, compassion and understanding, and is so keen to make you feel you belong, be so willing to violently punish you for changing your mind? I think many religions have thought this way, so I don't think this just applies to the Islamic example of this story. I also think we cannot understand this phenomenon if we restrict ourselves to thinking about Islam, for two reasons, there are many other religions, and all religions vary within themselves. So how can we better understand this?

Well, perhaps things will become clearer by applying the principles of Darwinian natural selection to the features we'd expect 'successful' religions to possess and exhibit. In this context a successful religion is one that is long-lasting and widespread.

What’s Darwin got to do with it? Well the beauty of Darwin's theory is that it can be applied to any system of replicators (that have high enough fidelity, i.e. copies are similar to originals) that exhibit variation and have to compete, and I think that these facets may apply to religion, so let's try to apply Darwinian logic to the spread of religions (this is a very rough sketch as I simply don't know enough about all the different religions and their history).

First, is this a justified approach? Well, religions replicate by converting other people to adopt their beliefs and practices, they do this both 'vertically', by converting naive children of believers, and they replicate horizontally, by converting other adults. Children will typically have no prior religion, adults may have an alternative already. Religions also replicate reliably, in that converts tend to adopt the same practices and beliefs as their teachers, although perhaps with some mutation, which creates more variation (other variation has to come from independent origins). This will lead to descent with modification, and thus a Tree of Religion (family tree) could be formed, analogous to the Tree of Life that Darwin used as his metaphor to describe the branching of lineages over time. Such branching reflects diversification, which will be more common when the mutation rate is higher, such as when the bible was translated into local languages across Europe leading to the plethora of Protestant denominations. Finally, they compete to occupy the hearts and minds of the finite human population, so yes, it seems Religions are subject to Natural Selection.

So, what features would we predict Darwinianly successful religions to have? That is, religions that are widespread and have persisted for a long time (and are probably 'organised'). Such religions will have high Darwinian fitness, which basically means they have high survival and high reproduction, but how will this be achieved?

Maximizing reproduction: religions should maximise both their vertical and their horizontal transmission, but focus on what is more profitable. Therefore, to maximise vertical transmission, one would predict that they actively promote biological reproduction, and will actively resist abortion and contraception. This is because children are likely to adopt the religions of their parents. This then is a sure way to increase growth and persistence (children are younger so will live longer into the future than you). This means that successful religions are unlikely to promote abstinence or castration, which is why you have probably never heard of the Skoptsy (http://en.wikipedia.org/wiki/Skoptsy)! As for abstinence, you may counter, ‘but what about monks and nuns?’ Well similar to how worker bees increase their overall reproduction not through having offspring but through helping their relative's offspring, Monks and Nuns could be argued to specialise in horizontal transmission, that is, they are a dedicated caste that specialises in helping the conversion and stability of others' beliefs, i.e. an educated caste that helps spread the word.

Horizontal reproduction tends to be more difficult than vertical transmission, because adults are less pliable, and may already have another religion. Therefore we would predict that coercion is more necessary, and that converting others would be a prestigious but arduous ‘mission’. Also, the most influential members of society may be targeted first, as they can convert others (like a pyramid scheme). This may explain why Christianity sent missionaries and the best medical practitioners to Norway to impress and convert King Olaf of Norway, who subsequently enforced that the whole of Norway, and then Iceland convert to Christianity in 999 AD. Hostile takeovers of opponent religions will also be favoured when competition is intense, as this has the double value of increasing reproduction and decreasing your rivals. Finally, murder within your religion will be a complete no-no, but murdering somebody in another religion will be relatively neutral or even positively valued.

Maximizing survival: survival for religion requires being immune to outside influences of other ‘belief systems’ (including science), and therefore one would predict that they praise blind, unquestioning faith (“Blessed are those who have not seen and yet have believed”, John 20:29), and strongly resist facts that they find to be contradictory, such as the Earth goes round the sun (time from Galileo to acceptance by Catholic Church – 350 years http://www.nytimes.com/1992/10/31/world/after-350-years-vatican-says-galileo-was-right-it-moves.html)

And this is where apostasy comes in, as it is akin to death, and therefore anything that reduces it will be favoured, such as extreme punishments such as death. It is worth noting that the punishment of death was delayed for 3 days, to give the woman the chance to recant and return to Islam (+1 compared to losing her). After refusing, the death penalty was sentenced (will result in 0, but prevents a -1 if she became Christian, and also acts as a deterrent to others), but will only be applied after she gives birth (offering another +1 for reproduction if the child is brought up Muslim). Of course when other religions are trying to convert each other, then a process of co-evolution will occur, whereby religions become better at converting others, and being immume from persuasion. This probably makes it easier to convert followers of less successful religions, rather than members of well established, Darwinianly successful religions, and why coercion is required in the latter case.

So in summary, even if religions start out as full of love for your fellow man and altruistic principles, and even if they are based on the truth, Darwinian Natural Selection would predict that the most successful religions will be those that have the following features; they favour reproduction, disfavor abortion, disfavor contraception, never favour universal sterility, but may perhaps have specialized ‘sterile’ casts that focus on horizontal transmission, and esteemed members that go out on special missions to convert others. They will actively fight opponent religious groups, use coercion to convert adults who have alternative beliefs, praise blind faith and disfavor skeptical inquiry, and will severely punish, perhaps with death, anyone who attempts to join another religion.

Of course this is a purely speculative academic exercise of little bearing on real-world issues, but evidence could come from seeing how religions change. If religions change, then we can see if they change to fit the above predictions. If they have not systematically changed, and truly reflect a creator, then maybe that creator makes things in accordance with evolutionary principles. What I really think would be interesting is to see where and when the above predictions (once ironed out theoretically) coincide with evolutionary predictions of human behaviour, i.e. maximising reproduction is clearly compatible with human evolution, but being a sterile monk is not, so how is this incompatibility reconciled? Can we predict who is more likely to become a monk, based on their biological circumstances? Is it people who were relatively more able to help their relatives in some way?