After travel through Alaska during the Second World War, in 1947 I went to Barrow with a very lively group of biologists. From their productive research developed the Arctic Research Laboratory. While we examined the rather surpris ingly modest metabolic rates of arctic warmblooded animals in cold, PER SCHO LANDER proposed and then carried out measurements of metabolism of some tropi cal animals in Panama. The differences could be formulated to show the basis of adaptation to arctic cold and to tropical warmth. Imagination and logic were required to formulate the comparison so that it could...