To answer this question, we must trace back to the source from the perspective of evolutionary chemistry and understand the evolution of vertebrates.
The earliest vertebrate Kunming fish appeared 530 million years ago, 423 million years ago, fish evolved into upper and lower jaws, which is the first full-jawed fish with a "mouth", and 375 million years ago, the most quadruped-like fleshfin fish TiTaleq fish appeared. Their fins have evolved into fleshy fins with wrist bones, which can support the body and crawl to land. They are small steps. 367 million years ago, the fleshfin fish finally landed on land with its strong fleshfins and breathing lungs, and evolved the first terrestrial vertebrate-ichthyosaur. Fishbone was also the first amphibian.
The main characteristics of amphibians:
Abnormal development, such as tadpoles breathing with gills, no limbs, a tail, living in water, and growing four feet in adulthood, each with five toes; It has primitive lungs evolved from swim bladder; Long eyelids; It has a fish-like tail fin, which is oblate; Amphibians began to develop the middle ear and could hear the sound coming from the air; You can only see horizontal prey, such as worms and insects; It has two atria and 1 ventricle (two merged and completely connected ventricles), belonging to a three-cylinder heart; Arteriovenous blood mixed circulation; Thermotropic animals have hibernation habits; Based on the neck, there is a movable joint between the head and the body; Move your eyes to your head.
This first amphibian, ichthyosaur, has four limbs, each with five toes. This is the result of biological evolution and natural selection, because limbs are symmetrical and easy to balance and move. Five toes are most suitable for crawling and supporting the body on the ground, and natural selection is often the best choice. With one toe, the ankle becomes inflexible, which is not conducive to crawling. Without one toe, it is not conducive to paddling and supporting weight.
With the different living environment and niche, the limbs of vertebrates have changed, but their shapes have also changed. For example, in birds, only the forelimbs have evolved into wings, and the toes and claws of the forelimbs have obviously deteriorated, but the hind limbs have become strong and powerful. With the acceleration of running during takeoff, the hind limbs have only four toes and claws, because they live in trees.
A cat has five toes in each forelimb, four toes in each hind limb, five toes in each forelimb for catching prey and four toes in each hind limb for running.
The evolution of horses, on the other hand, is the increase in size, the increase in crowns and the decrease in the number of toes, from the initial four toes to three toes (the famous three-toed horse), and finally evolved into a real horse with only one hoof, which is conducive to galloping on the vast grassland.
And humans are the earliest primates, (Achilles monkey), passing through forest apes, Chad apes, ancestor apes and Afanan apes. They are all higher primates with four limbs and five toes. From the earliest arboreal life, they can walk on the ground with their toes. For example, chimpanzees walk with forelimbs and knuckles.
The forelimb has five fingers, which is convenient for grasping and is beneficial to making and using tools; The hind limb has five toes, which is convenient for supporting the body to carry heavy objects.
Therefore, the number of toes of vertebrates, whether it is a toe (hoof), a horse that is good at galloping grassland, a bird with only two limbs and four toes, and the most intelligent human being, can not only manufacture and use complex and precise instruments and tools, but also go into the sea from the sky, which is almost omnipotent. Now is the era when human society is highly civilized and science and technology are extremely developed. The speed of progress is getting faster and faster, and the prospect is almost unpredictable. Let's look forward to the future together!