The appeal to “nurture” as a cause of behavior is nothing more than a sentimental appeal to magical belief in “conscious” control of the biology which determines behavior. A biology that is immune to any conscious awareness, let alone influence and control.
The claim that “nurture” determines the effects of nature or biology, via epigenetics, for example, is special pleading while trying to obscure the remaining determinism of the genetics and biology of behavior.
But the magical/faith-based ideology and set of cultural beliefs in both conscious control of behavior, and the accompanying biology of the genes, body physiology and brain, and the ability of every individual – using everyday language (mainly academic English) – to perceive and accurately describe the biological and environmental factors causing behavior! It is a silly idea but no more silly then belief in gods and voodoo.
By definition, the molecular structure of the genes is the foundation of all behavior (phenotype). Sure, the environment, “nurture”, effects the expression of the molecular basis – but that molecular basis remains the main determinant of the behavior – the “first cause.” How much the environment changes the expression of the genes is an empirical question but I would guess it is a smaller effect. Is it 80% – 20%? 80% genetics. I’ll bet.