Renowned MIT linguist Steven Pinker engaged an audience of 400 in the classic nature versus nurture debate last night—saying heredity plays a more dominant role than many behaviorists of the last century have asserted.

Speaking at the Askwith Forum at the Graduate School of Education, Pinker denied the possibility of poet Philip Larkin’s well-known adage that your parents “f--- you up, your mum and dad / They may not mean to but they do”—a passage he quoted, to the delight of the crowd.

He said the role of nurture is often overestimated.

Pinker’s talk focused on the material in his new book The Blank Slate. Currently at number 10 on the New York Times Best-seller list, the book explores the notion of human nature and its moral and political implications.

Pinker synthesizes research in language, cognitive science and evolutionary psychology to produce a theory of human nature that repudiates long-standing doctrines such as the “blank slate,” “the noble savage” and “the ghost in the machine.”

During the hour-and-a-half discussion, Pinker explained how these ideas, which he analyzes in his book, have led people to see “human nature as dangerous.”

Pinker attempts to refute this modern denial of human nature.

Pinker emphasized that while critics have argued that attributing humanity to genetics alone results in a determinism that diminishes peoples’ sense of responsibility, the implications of his theory don’t automatically lead to pessimistic assumptions.

He said that politics and social theory need to be recast in a way that takes into account evidence that humans are in large part products of our unchangeable genetic makeup.

One of Pinker’s most controversial assertions last night was that family environment has no significant effect on variations in character or personality, and that “virtually all the differences in parenting within a family can be explained as reactions to the genetic differences that the children were born with.”

Pinker said evidence from the study of adoptive children and identical twins is particularly important in that identical twins reared apart are often very similar and “adoptive children reared in the same environment are not at all similar.”

He went on to say that “virtually everything—save factors such as religion or language—have a degree of inheritability greater than zero but less than 100.” Pinker addressed his critics’ objections that a theory rooted in biology suggests that if there were no long-term consequences, then parental treatment of children is inconsequential.

“Of course it matters how one treats their children,” he said. “It matters to the degree that the quality of every relationship, in order to build deep and satisfying relationships, hinges on mutual respect.”

Pinker added a material incentive to the moral imperative.

“Children grow up with memories of how they were treated and one should be weary because, ultimately it is your children who will be choosing your nursing home,” he quipped.