【答案解析】Nature began a new experiment. Instead of adapting to a specific environment, man has the capacity to adapt himself to any specific environment. They spread throughout the globe, changing as they moved, until they became the most widely distributed species on the earth. Man adapted physically as well as culturally to the new surroundings into which he moved. People who lived near equator developed dark skin to protect themselves from strong sunlight; people who moved to colder climates developed light skin to take advantage of the sunlight for the synthesis of vitamin D; people in cold dry climates became stocky to conserve heat. People in hot dry climates tended to become tall and thin to dissipate heat.