Big history examines history across long time frames using a multidisciplinary approach to understand changes in the human experience. It looks at how scientific discoveries fundamentally altered civilization's perceptions of the world. Key events that transformed humans included a genetic mutation that improved brain organization, allowing symbolic thought, and competition between groups that forced technological innovation. A major catastrophe around 535 AD caused global climate changes, famines, and plagues, likely due to a large volcanic eruption. Differences in continents' long term histories were not due to innate qualities but environmental factors, as locations like Europe and Asia advanced more quickly than areas like New Guinea. Global trade spread new resources and diseases between continents.