you found how the specific metabolic rate (food consumption per unit mass) varies with mass. If all animal heart volumes and blood volumes are proportional to M, then the only way for the heart to increase the oxygen delivery to the body is by increasing the frequency of the heart rate. [Schmidt-Nielsen (1984), pp. 126150.] (a) Using the result from problem 41, if a 70 kg man has a heart rate of 80 beats min1, determine the heart rate of a guinea pig (M = 0.5 kg). (b) To a first approximation, all hearts beat about 800,000,000 times in a lifetime. A 30 g mouse lives about 3 years. Estimate the life span of a 3000 kg elephant. (c) Humans live longer than their mass would indicate. Calculate the life span of a 70 kg human based on scaling, and compare it to a typical human life span.