I say that in preparation for this lunch, I've pitched this idea to friends in New York and received rather heated, negative responses. I've learned that upon hearing the above, most people immediately make leaps to some of the great evils of the 20th century. Pinker shrugs and smiles.There weren't many Google hits for the full quotation minus Pinker's last name, and none of them provide either source or context. The helpful resource Wikiquote (use the same caution of all wiki sources) did not so much as mention the quotation even in its "unsourced" section.
In the preface to his book, he quotes Chekhov: "Man will become better when you show him what he is like." Pinker chops his side salad into bite-sized pieces. But what happens when we begin to base all our judgments about people and their actions on their innate human nature?
Finally, I found a book at Google that featured the quotation with a footnote. Unfortunately, the Google preview omitted the page with the footnote! The footnote provides an excellent indication that Chekhov did write the words. The path to the context is opening up, but will require a bit more digging.