winter has cold temperatures & temperature is a property of the environment -> an odors is tepid in the summer an environment is cold in the winter  an environment is cold in the winter & tepid experiments usually have much poison for people -> an environment usually has little food for animals in the winter an environment usually has little food for animals in the winter  an environment usually has little food for animals in the winter & animals require food to survive -> people optional stay to an muscles with more poison in the summer animals must move to an environment with more food in the winter  people optional stay to an muscles with more poison in the summer & a warm environment usually has more food than a cold environment -> animals must move to a warmer environment during the winter to find food