Why there are no three-legged animals?

Some animals living mainly inwildlife, have a unique feature - they use their tail as an additional support when standing on trees. Vivid examples of this behavior can be the sloths that inhabit the jungle of South America. Why did evolution endow these animals not with an extra, more stable foot, but only with a “standard” tail? Well, let's try to sort this issue out together.

Why doesn’t three-legged creatures exist in nature? It seems that the DNA of sloths can answer this question.

Why do animals have four legs?

As you know, most animals in natureuses a pair of limbs, designed to meet certain needs. So, meerkats in an upright position rest on their tail and hind legs, and well-known woodpeckers use tail feathers to lean more firmly on a tree trunk.

However, the ability to stand on only twothe hind limbs requires a fairly large expenditure of energy, since vertical standing imperceptibly does a certain muscular work. Despite the fact that the hypothetical presence of a third hind limb in a living creature does not require any energy expenditures, researchers believe that the pair of legs and paws of all living creatures on the planet is recorded by nature in our DNA.

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Many woody animals use their a specific tool for additional grip and support when climbing trees. The presence of two long legs prevents the kangaroo from walking, like many other mammals. That is why they use their strong tail and forelimbs as “tools” to help the kangaroos push their hind legs off the ground during grazing.

Kangaroo tail helps the animal push off from the ground when “walking”, playing the role of an additional supporting limb

According to scientists, so widespreadthe peculiarity of the living creatures of our planet was built into our DNA at one of the earliest and oldest moments in the process of evolution of life, even before the first living creatures that populated our planet had their first appendages, which later became legs, fins, paws and fins. Once this feature of bilateral symmetry was captured in our DNA, it was already impossible to change.

If you carefully observe nature, thenwe can see the law of symmetry literally in everything, not only in the paired structure of most organs of living organisms. Most likely, the presence of just a pair of limbs helps animals acquire better mobility and ability to survive. In addition, this type of symmetry is in excellent agreement with the structure of our central nervous system, since it is the spinal cord that controls the pair of legs and feet, passing through the very center of our body. The third functional limb, in this case, would sooner or later turn into a useless rudiment from which mother nature favorably protected us.

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Despite the fact that a person used toto observe the two-legged creatures that inhabit our planet, it can be difficult to imagine the mechanism of movement of the three-legged creature, such unusual organisms may well live in distant stellar systems that humanity has yet to study. If so, then biologists of the future may be able to rewrite the entire theory of evolution that exists today.