Man adapted physically as well as culturally to the new surroundings into which he moved. Those who stayed in or moved to equatorial climates developed dark skin to protect them from the rays of the sun. Those 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.