Abstract: <br /> Many aspect of human behavior are attributed to culture, but the <br /> dynamics of cultural evolution are poorly understood. Biologists have <br /> often claimed that culture is largely shaped by a genetically <br /> determined human nature. Social scientists, in contrast, claim that <br /> culture is "free", meaning "free from genetic influences" but also <br /> "free to take any direction". Here I show, with simple mathematical <br /> models, that culture does not freely evolve, even in the absence of <br /> genetic influences. The models show that culture itself generates <br /> forces that systematically bias the direction of cultural evolution. A <br /> short review of ideas about cultural evolution within the social and <br /> biological sciences introduces the talk. <br />