Today we are starting a series of three extremely interesting articles explaining the basic principles of living organisms on our planet. Among them, the rule of the 3/4 comes to the fore.
The respiratory system of insects consists of a system of gaps - tracheas and spiracles - holes scattered over the surface of the body through which air under atmospheric pressure is pushed into the body. It is a simple and reliable system, but it only works well over a distance of a few centimeters. 300 million years ago, in Carboniferous, while dragonflies with a wingspan of 75 centimeters flew over the earth, those days the air contained more oxygen than today.
Today, a two-meter cockroach is the same as a strangled cockroach. And also a cockroach with broken legs, because if the insect was enlarged to the size of an elephant, its legs would collapse under the weight of the body.
The strength of bones and muscles depends on their thickness. If we enlarge an animal four times, its bone strength increases sixteen times. However, the weight will grow more, because it is proportional to the volume, i.e. as much as 64 times. Larger bones, though stronger, will not hold him.
About cooking elephants
The dung beetle can carry a load of 400 times its weight, but a human can hardly lift another human, and an elephant will not be able to walk with another elephant on its back. In turn, miniaturized octopuses would sink in water like in honey, unable to move - because at these sizes they would be bound by the forces of water cohesion.
If a human wanted to use the surface tension of the water to walk on its surface like a water explorer, he would have to stretch his limbs seven kilometers (!).
These examples show that in biology, the concept of "the same, only greater" is irrelevant. Knowledge of the rules governing ant life is of no use to us when we want to infer anything about whales. Elephants are not big ants. Size matters and that's enough!
How different the laws of physics are against this background. Big and small balls fall from the tower in the same way, and gravity does not treat bread crumbs and large space bodies differently. Simple scaling laws do not work in biology.
Are there any principles in the science of life that would work on all scales of magnitude?
When looking for fundamental laws, let's start with what drives life. Where do animals get their energy from? From burning in the cells. The greater their volume, the more cells they have, and the more energy and, by the way, more heat. However, you need to know how to properly manage it, which is why the cooling capacity seems to be equally important. This in turn depends on the surface of the body through which the heat can be radiated.
Small animals have a large body surface area in relation to their volume, so they do well where excess heat is a problem, for example in equatorial regions, and much worse in cold climates. That is why there are large animals in the polar regions: seals, walruses, or bears, not mice or butterflies. Relatively small penguins "cheat" nature, gathering in herds during the winter, thanks to which they become one large organism.
What is the conclusion of this? The smaller the animal, the greater its heat loss and the more calories it has to burn to replenish the lost energy.