An extinction event is not a 'cause' of evolution. The only cause of evolution (change of form), is genetic mutation, and it's effects are always gradual.
Well you have put your finger on the crux of my disagreement with Darwinism. It has to do with the nature of causality itself.
Darwinists are methodologically committed to locating causality at the smallest possible level. In fact this micrological approach is the definitive characteristic of Darwinism. For Darwin himself, the smallest possible level was that of the individual organism. Today, Darwinists like to locate causality at a yet more micrological level--that of genes.
But throughout the history of Darwinism, the basic assumption remains the same: events are best explained by looking at the smallest possible causal elements.
I take the opposite view. I think explanations are at their fullest and most convincing at the largest possible level. So I would say that the final cause of evolution is the collision of distant galaxies that produced the comet that smashed into the earth that made the dinosaurs extinct.
Part of the problem is the conceptual poverty of the English language. We only have one word for "cause," whereas classical Greek had at least four. So we are basically unequipped to make the fine distinctions between various kinds of causality that questions such as evolution demand.
But I don't really want to get into a philosophical discussion about causality here. For the purpose of this thread, I just want to note that Darwin's method is borrowed wholesale from Adam Smith. Smith thought the actions of individuals was the key to understanding what he called the "economy."
Obviously no socialist or anti-capitalist of any kind can endorse that assumption. And yet they seem happy enough to endorse the very same assumption when it occurs in biology. I suspect the reason is that few of them have much knowledge of biology. Either that or they are so paranoid about appearing metaphysical that they miss this vital contradiction in their thought.
And make no mistake, this contradiction is indeed vital. I would go so far as to say that it explains the failure of the Western Socialist project
tout court. If I can bothered I will return later on to explain why.