There's considerable speculation in this book, but the author shows a through understanding of evolutionary theory and the literature. I enjoyed reading about the author's intellectual journey into a scientific field that he initially knew little about but that over the years entirely changed his understanding of human vulnerability to both physical and mental illness, especially the so called diseases of civilization. The scientific revolution that is transforming psychology, psychiatry, and even the social sciences owes a lot to the pioneering scholars from the U. of Michigan (Alexander, Neese, Axelrod, Low, Betzig) and to the many who visited or spent some time there (Hamilton, Williams) . I especially liked the discussion of substance abuse. I amuse my students by telling them that THC and nicotine are natural insecticides but far less harmful to them than ingesting DDT. Now I can refer them to the author's book.