Saturated fats have long straight tails of fatty acids, while unsaturated fats have kinks in their tails created by the double bonds. the kinks prevent the fatty acids from packing together as tightly. ectothermic (cold blooded) animals need to keep their membranes fluid at cooler temperature and thus contain their membranes.

Which of the following best describes the expensive tissue hypothesis? brains require more energy, so the gut had to be reduced, and larger brains and tool use led to higher quality diets. increasing body size means that homo neanderthalensis had to include more fat in its diet. brains require more energy, so the gut had to be reduced as brains got bigger. brains require more fat, so the gastrointestinal viscera (gut) had to expand, and hands were needed to acquire more food.