And an interactionist. From Obedience to Authority:

A potential for obedience is the prerequisite of such social organization, and because organization has enormous survival value for any species, such a capacity was bred into the organism through the extended operation of evolutionary processes. I do not intend this as the end point of my argument, but only the beginning, for we will have gotten nowhere if all we can say is that men obey because they have an instinct for it.

Indeed, the idea of a simple instinct for obedience is not what is now proposed. Rather, we are born with a potential for obedience, which then interacts with the influence of society to produce the obedient man. In this sense, the capacity for obedience is like the capacity for language: certain highly specific mental structures must be present if the organism is to have potential for language, but exposure to a social milieu is needed to create a speaking man. In explaining the causes of obedience, we need to look both at the inborn structures and at the social influences impinging after birth. The proportion of influence exerted by each is a moot point. From the standpoint of evolutionary survival, all the matters is that we end up with organisms that can function in hierarchies.

I’d take Milgram’s endorsement of interactionism one step further and say that “the proportion of influence” isn’t just moot – it’s nonsensical. You don’t have a human mind unless you have inborn mechanisms and social influences working in concert with each other.