Surely there could not be an equivalent ensemble of fitness in nature for some other type of life.
As every medical student comes to learn when first dissecting the human body at medical school, our limbs are almost entirely composed of muscles.
It is very doubtful that any beings in the universe could develop a civilization remotely comparable with our own without the use of metals.
Self-evidently, the gravity on the surface of a planet limits the maximum size of large terrestrial organisms.
As we have seen so far in this series, fire was an absolutely crucial component in humanity’s rise to civilization and technology.