[S]ome form of secular humanism [...] argues that humans are genetically programed not to lie, murder or steal, therefore this is both the right morality & the one they practice. This, to my mind, is committing the naturalistic fallacy.

It is naturalistic fallacy. You should avoid murdering people not because evolution programmed you to do so, but because it's the behavior you prefer to implement. That you were also (causally) created as you are by evolution is another issue entirely: the difference becomes important where you see some of the features implemented by evolution as (normatively) undesirable. It doesn't even have to be something to do with change in the environment, it may well be something that works as "intended". See Which Parts Are "Me"?, and more generally the Metaethics sequence.