Scientists are often materialistic totalitarians, arguing (sometimes rather presumptuously) that this is strictly a stuff and energy universe. Mysticism that involves the supernatural--that is, things not just made of stuff and energy--is sneered at. Everything is causal: if you see an outcome, there must be a cause, and it is often argued at least implicitly that any cause is essentially inferrable. Nothing is left to chance, even if it may superficially appear so.
When it comes to life, material fundamentalism argues that all that we are, including all we think, is stuff and energy, cause and effect. If so, then molecular genetics will eventually be able to account for everything (and, it's often argued, in terms of Darwnian natural selection).
Science regularly discovers new kinds of natural factors, and they then join the panoply of materialist causes. We must be open to the possibility that our understanding of what is 'material' may change if we discover some truly other phenomena which we can call 'dark matter' as a general kind of term: factors not previously known or suspected. What we think of as 'material' may have to include new things.
On the other hand, scientists don't accept explanations that argue on the basis of such unknowns. That's often characterized as 'mysticism' or 'superstition'. In the absence of evidence acceptable from a marialistic point of view, that's one major reason scientists oppose or don't accept religious explanations of the natural world.
If every instance of a phenomenon, say every case of a certain type of cancer, has a different material explanation, then the usual kinds of cause and effect approaches don't work very well as explanations. Science is currently based largely on repeatable observations. Individualism can therefore be a problem.
These thoughts were triggered in part by watching a video of a BBC television series called The Impressionists. It is a very fine dramatization of the 19th century French impressionism movement in art: Degas, Manet, Monet, Cezanne and others. At the same time these painters were working, realist painters were working as well (and there was conflict between the two groups, of course). So why did impressionism arise? Why is impressionist art so impressive (to some, at least)? Can anyone seriously argue that groups looking at the same object saw it in such different ways as a result of having different genotypes?
In what meaningful sense is impressionism to be explained in material terms? Certainly Monet saw through a retina made of cells and photoreceptors, and his brain was made of neurons that connected via neurotransmitters and receptors. At least, we need not argue literally that Monet got his impression directly from God (or, as realists might have argued, from Satan!). And why are eyes that evolved to perceive the real world also vulnerable to liking rather than fearing blurred and hence untrustworthy interpretations of Nature?
Explaining things that are strictly material may not always be possible in meaningfully material terms. This message uses 'ink' and images of 'letters', but cannot be understood in terms of ink and letters. It is understandable both from cause and effect viewpoints in its organization, the higher-level interactions (which may include true probabilism), and these are indeed also 'purposive' in some senses--Degas painted for a reason, saw things as he did for a reason.
Accounting for complexity, for the way that countless interactions yield, or cause, coherent and unitary outcomes, is a major challenge for science, and perhaps especially for biology, because although we're made of atoms that act as automotons--each hydrogen is the same, so far as we know--at least for practical purposes, our components change and react to circumstances.
So genetic variation, if properly understood, may account for very general traits like 'fidgetiness' or 'anger', but not for the higher-level or more specific aspects of culture. Culture evolves in its own way (a subject for future posts), and constitutes environments in which traits like impressionism arise.
But esthetics are a good example of things we should not expect to be explicable in molecular terms, even if Manet and Monet were made of nothing but atoms.