Homeothermic birds and mammals maintain a constant body temperature by behavioral and physiological adjustments. The latter includes changes in heat production, blood flow, and evaporative water loss. Poikilothermic reptiles also maintain a stable body temperature (often higher than that of mammals) when environmental conditions allow, by using behavioral and physiological mechanisms. Both modes of life have advantages and disadvantages. Neither poikilothermism nor homeothermism is unquestionably advantageous under all conditions; therefore, neither group of animals is indisputably better suited for survival than the other. God created all animals equally fit to live in their respecitve niches.