In his book "A Short History of Nearly Everything," Bill Bryson explores various aspects of human biology and behavior, using the growth rate of a man's beard as an example. He notes that this physiological change is influenced by psychological factors, specifically the connection between sexual thoughts and physical responses in the body. When a man thinks about sexual ideas, his testosterone levels rise, which can accelerate the growth of facial hair.

This observation highlights the intricate relationship between mental states and physical changes in humans. Bryson’s work encourages readers to consider how various aspects of human life, such as hormones and thoughts, intertwine to shape our biology and experiences. It serves as a reminder of the complexity of human existence and the unexpected ways in which our minds can influence our bodies.