The Mismeasure of Man written by the Harvard paleontologist Stephen Jay Gould (1941-2002) is a controversial book. Gould criticises the methods and motivations underlying biological determinism, which means that biological factors such as an organism's individual genes completely determine how a system behaves or changes over time. The book also attempts to critique the principal theme of biological determinism, that "worth can be assigned to individuals and groups by measuring intelligence as a single quantity". Furthermore Gould discusses two techniques used to measure such a quantity, craniometry and psychological testing.