I don't think it
should be surprising if biologists are the least likely group to believe in God.
One common reason for believing in God is how ingeniously designed living things often are. The reason why this turns out not to be a very good reason is that evolution explains this better (dealing e.g. with cases where the design seems needlessly complex, malicious, etc.). Biologists are more familiar with evolution and spend more time thinking about it than other scientists.
Relatedly, evolution has frequently been the target of attack from religious people and groups. Biologists are likely to notice this more and be more bothered by it (imagine a world where there's a strong anti-technology lobby motivated by religion; engineers would likely be more likely to be opposed to religion in that case).
Pure mathematicians are used to thinking of intangible things like numbers, sets of sets of sets of sets, equivalence classes of functions from manifolds to abelian groups, etc., as real things even though they clearly don't "live" in the physical universe, and perhaps even as more perfect than the tangible inhabitants of the material world. I think this may make the idea of a sort of spiritual universe with inhabitants like a Most Perfect Being Imaginable particularly congenial to pure mathematicians.
(On the other hand, pure mathematicians ought to be less vulnerable to some varieties of philosophical flim-flam used by religious apologists. For instance, the so-called "ontological argument" is composed mostly of logical errors, and I would expect pure mathematicians to notice this more readily than anyone else. ... But: Kurt Goedel, who was one hell of a good logician, actually put some effort into coming up with a logically sound version of the ontological argument. Of course it's no good because it relies on axioms there's no reason to think apply to the actual world, but it does indicate that a sufficiently ingenious mathematician may react to a terrible argument not by dismissing it but by finding a way to make it less terrible.)
[In case anyone cares: I am a pure mathematician, or at least I was one before moved into industry where one gets paid more for doing easier work. I was a religious believer for many years but am not any more.]