# Rate of living theory  The rate of living theory grounds itself in the observation that larger animals have a lower metabolic rate than smaller animals. Metabolic functions include breathing, circulating blood and maintaining body temperature. For instance, mouses have to expend more energy than elephants to keep their bodies warm since their surface to volume ratio is much greater. Metabolic rate is here thought of as a "rate of living": slower rate of living would yield a longer lifespan. --- ## 📚 References - "Can Calorie Restriction Extend Your Lifespan?" Science in the News, 2 Aug. 2020, <https://sitn.hms.harvard.edu/flash/2020/can-calorie-restriction-extend-your-lifespan/>.