All mammals have about one and a half billion heartbeats in their lifetime. Scientists wondered why animals have the same lifespan, equal to this number? Kenya Wildlife Service specialists monitored heartbeats and found out that the interval between heartbeats depends on the weight of an animal. The bigger the weight is, the slower the heart beats. An elephant weighing four tons has a heart rate of about 30 beats per minute, with its heart beating about once every two seconds. A lion weighing 200 kg has a heart rate of 60 beats per minute. A rat weighing 25 grams has a heart rate of 800 beats per minute. The heart pumps blood, which carries oxygen throughout the body. The end goal is the cells. This is what enables metabolism. All cells are the same size, but larger animals have more of them. Let’s say one animal has grown in height, so its length and width have increased, but its body shape has remained the same. Scientists have calculated that if these figures are doubled, the body volume will increase eightfold. The number of cells will also increase by the same amount. All these cells need energy. Small animals use a lot of energy, while large animals use less. Why so? It all depends on the fact that large animals have low cellular activity. Let’s imagine that if an animal becomes 10 thousand times larger, the metabolic rate will drop tenfold, and only 0.1 of the metabolic energy will be needed per second. The heart rate will also decrease tenfold. A whale’s heart beats several times a minute, while a shrew’s beats more than a thousand times. Smaller animals require more energy because they have fewer cells that constantly function at a high rate. Therefore, their heart works more intensively. With larger animals, the situation is the opposite. The heart rate is directly proportional to the square of one-fourth of their weight. If the weight increases tenfold, the heart slows down to half of its initial rate. This rule is applicable to all mammals. All of that says that there are mathematical laws of nature.

The dependence of heart rate on body size also correlates with human biorhythms. The heart of an infant beats quickly – about 130 beats per minute. The increased heartbeat causes the blood to circulate at a high speed. The circulatory system also works quickly. All biorhythms are accelerated, so everything that happens around the child seems slow to him. But as it grows and matures, the heart slows down. The biological clock slows down, and changes in the surrounding world seem to be quite fast to an adult. In childhood, metabolic processes are fast – time outside the body seems slow in contrast. With age, metabolic processes and the heart slow down – time seems fast in contrast. In absolute terms, time is the same, but biorhythms are different. This rule applies to any living organism, including humans. Even if they are at the same spot, time is perceived differently. If a person can feel the difference between chronology and biorhythm, then how do animals perceive time? For example, rats have a high heart and breathing rate. They grow quickly and so they die. For small animals, time flies quickly. Large animals seem slower in comparison, for them time flows more slowly. Life expectancy also depends on size: the larger the species, the longer it is. The fact that all mammals have the same number of heartbeats from birth to death suggests that the entire course of life is subject to certain rules – the mathematical laws.