With his bestseller Guns, Germs, and Steel, Jared Diamond stimulated discussion over the forces that have shaped humanity. In The World Until Yesterday, the Pulitzer Prize-winner examines tribal and pre-tribal societies for what they can tell us about our own WEIRD (Western Educated Industrialized Rich Democratic) world. He finds that in most traditional cultures, the elderly are better treated and less socially isolated (even if life expectancy is shorter) and that on-demand breastfeeding (rather than at mom's convenience) has much to recommend it. Diamond has spent much of his life doing field research in New Guinea. At his first encounter in 1964, most inhabitants ate a low salt, low sugar diet and were lean, muscular and physically active. The introduction of Western ways has resulted in paunchy New Guineans suffering from diabetes and heart disease.