Razib has a little post on cultural cladism, but I think he gets it quite wrong.
He repeats the usual
trope canard that culture isn’t like biology in terms of its evolution. I think it is exactly like it, and that the “analogy” between cultural traditions and species is quite exact. All that differs is the frequency of the various kinds of evolution.
For instance, take Razib’s example. He says that because Judaism is very unlike Christianity in some respects, and much more strictly like Islam in its monotheism, it should be seen as a sister taxon to Islam and not Christianity, and the term “Judeo-Christian” should be dismissed. I have my own objections to “Judeo-Christian”, which I’ll get to in a minute, but let’s consider the philosophies of classification used here.
The historical tree might seem to be this (figure, A). Judaism coalesced with the “reforms” of Hezekiah, and most historical scholars think that was the foundation of that religion. It was when the Torah began to be formed and the rituals were established, although something akin to modern Judaism didn’t develop until the end of the 7th century BCE with the reign of Josiah after the return from exile.
Christianity developed, as is well known, out of the messianic cult that had strong connections with the P’rushim (pharisees) in Judaism of the first century CE, and which was eventually melded with classical culture of the Roman era. Islam was a reaction to the polytheistic folk religions of the Arabian peninsula, and to the Jewish and Christian communities in that region. Mohammed was something of an eclectic, in that he adopted the Jewish form of monotheism, but he also adopted the universalism of Christianity. Islam was for all people, as was Christianity, not merely a given ethnic group. Depending on what you choose to measure each religion against, you get differing historical connections.
Now with three “taxa” there are three different cladograms. Note that a cladogram is not the same as an evolutionary tree – it is a classification. It roughly says that “A is more closely related to B than either is to C”, but “closely related” can mean “more recently descended from a common ancestor” or “more similar” or a bunch of other things. If you have n taxa, there are (2n-3)!/[2n-2(n-2)!] possible trees, so with 3 taxa you get 3 trees. I give them here as B – (Judaism, (Christianity, Islam)), C – (Christianity, (Judaism, Islam)), and D – (Islam, (Christianity, Judaism)). What these man in terms of evolutionary history is another matter.
If we classify according to the overall totality of characters – monotheism, ritual, law, doctrine, and so forth, based on modern religions, then we might think that Razib is right – Judaism and Islam are both strongly monotheistic, while Christianity, with its Trinitarian doctrine, is compromised, and both Judaism and Islam have strict ritual requirements of their adherents, while Christianity doesn’t, such as ritual washing and the like. But this would overlook the fact that initially Christian traditions fought violently, literally and metaphorically, over their monotheisms, and what we have under the so-called Nicene version of Christianity is actually a much derived form of religious belief compared to earlier schools of thought (the Trinitarian doctrine is late – 3rd century). Moreover it will overlook that there are many kinds of rituals, and no Christian tradition has been free of rituals until fairly recently. It is very much a matter of what you choose to call a “ritual”. So if you drew a tree in the 2nd century, catholic Christianity and Judaism might pair up against a third alternative (say, the Paulicians, a form of gnosticism) or even against the much later Islam.
Moreover, we can usefully see the rigid monotheism of Islam as inheriting a “plesiomorphy”, which is to say an underived or ancestral state, from its Jewish heritage, rather than seeing the evolution of these religions as irrelevant to their classification. Plesiomorphies in cladistics are uninformative – having four limbs is not informative about the evolution of tetrapods. Not having limbs is informative about the snake clade. To find tree C intuitive, as Razib does, you have to focus on those character states that are more similar, but I wonder if the history of those religions really does support C rather than B. I take it that nobody (but extremist Muslims, perhaps) thinks that tree D has any cogency.
Classification of this kind is intended to use the totality of evidence to group historical groups. There is, as Razib noted, another kind of classification – phenetics. Phenetic comparisons are useful, in a way, because they make explicit the similarities used, and they are able to mark the degree of difference, but they are arbitrary in their divisions, and worse, they are highly sensitive to the characters used. If you use one set of components in your analysis, you get one grouping, but the very same taxa or specimens can be regrouped in a radically different manner by choosing other characters.
The difference between phenetic and cladistic classification can be summarised thus: a cladistic classification allows you to identify groups within which you can predict that many characters will be shared, compared to the outgroup, even if those characters were not used in the initial classification; while phenetic classifications are only good for the characters used in the analysis. You can inductively generalise a cladogram, but you can only deductively infer from a phenogram.
On the other hand, a cladogram is only good when you actually have independently evolving lineages. Cultural evolution is thought by many to be constantly recombining, and this would swamp a phylogenetic signal. If Islam is a “hybrid”, then the historical tree would look like this (E):
Which side of the hybrid lines one makes dotted will depend on which side contributes the most. I think that the Jewish element is influential but less so than the Christian. Mileage may vary. If the matter is not decideable, or is arbitrarily reliant upon choices of characters, then we have an unresolved tree, in this case a trichotomy.
The point of all this is to show that intuitions here are not reliable when it comes to classifying in either biology or culture. There are issues that need to be resolved in a fair bit of detail. I haven’t even begun here to discuss the varieties of sects in each religion – the CHristian and post-Christian sects number around 1500 in the US alone, and the number is probably much higher. There is a kind of cladogram of Christian religious denominations, the main ones, here. Islam has its own separate traditions, at least five. And Judaism has numerous diverging traditions, usually grouped into the Orthodox, Conservative and Reform, but also including such things as the Kabbalist traditions, and Karaites, and so on.
Two final points: The “Judeo-Christian tradition” is a construct in itself. It doesn’t really give much in the way of characters, nor is it a coherent tradition. On cladistic grounds, it would be a paraphyletic group, formed by excising the Islamic lineages arbitrarily. If we adopt the less offensive “Abrahamic religions” (since they all claim Abraham as their founder in one way or another) we lose what the Judeo-Christian term is supposed to capture. If we adopt a crown clade definition, then you might have the Christian-Islamic tradition, which makes more sense of a lot of the interactions between the West and Arabian East. Sibling fight more than cousins…
Finally, we should note that we can identify these traditions, irrespective of occasional cross-lineage borrowings, just as we can for languages, styles of art, and so on. There are “species”, or at any rate, taxa, in culture as in biology, and they are tolerably salient. Given the complexity of biological taxa once you stop obsessing on things with fur and feathers, it should come as no surprise that culture has taxa too, and that we can use cladistic methods to analyse it. As a postscript, let me direct readers to
Mace, Ruth, Clare J. Holden, and Stephen Shennan. 2005. The evolution of cultural diversity: a phylogenetic approach. London: UCL Press.
as an example of how this can be done formally (in this case on a variety of case studies).