In the first chapter of his 2003 book The Essential Difference, he discusses the bestseller Men Are from Mars, Women Are from Venus, written by John Gray in 1992, and states: "the view that men are from Mars and women Venus paints the differences between the two sexes as too extreme. The two sexes are different, but are not so different that we cannot understand each other."
In his 2003 book "The Essential Difference," he critiques John Gray's 1992 bestseller "Men Are from Mars, Women Are from Venus" by stating that the notion of men being from Mars and women from Venus overemphasizes their differences.  He argues that while there are distinctions between genders, these differences aren't so profound as to preclude understanding each other.