I don't think the disposition to evil needs a "fertile soil". For instance, there are evil men in convents--and in quite a high degree too--that harm others in order to break the monotonicity of their life; now, would you say a convent is a "fertile soil" for growth of evil--should be the contrary. The artificial spite is a product of, as I've mentioned, a boring and monotonous life, and it so happens the easiest mode available to break this is harm towards others.

In case of natural malignity, the influence on the actions lies not in something mundane as boredom but other natural causes--be it from parental abuse, &c. but I concur that I've no scientific knowledge in this field. And, thus I believe that the ones that hold malignity through nature (in contrast with the artificial one) are able to create an environment that accomplishes, or perhaps, breaks, as I've said above, their disorder's whims. And the chans happen to be a pre-existing place with like minded people that nurture each other's "seeds", but even in the lack of these imaginary soils, the seeds will grow without any problem.