In this talk I will describe how long-forgotten measures of linkage disequilibrium can be used to detect and measure past population structure. I will show how these can be used to infer population structure among early humans in Africa [mostly described in our paper A weakly structured stem for human origins in Africa], but also consider more recent extensions to detect natural selection and other demographic effects. Finally, I will describe an unexpected mathematical connection between population genetics and quantum mechanics that has unveiled new and (hopefully) informative measures of genetic diversity.