Amazon calculates a product’s star ratings using a machine learned model instead of a raw data average. The machine learned model takes into account factors including: the age of a review, helpfulness votes by customers and whether the reviews are from verified purchases.
I really liked David Reich's online talks and bought this book to get a recent summary of everything. It covers origins on all continents and in the Pacific, and looks at a few philosophical issues: racism, use of burial remains, indigenous reactions. I read this book straight through and finished it - I definitely enjoyed learning it all.