Why are there absolutely no three-legged creatures on Earth?

Science answers the question “Why?” and “Why not?”. Occasionally, scientists will find it extremely worthwhile to find out why some things never exist: A creature with three legs, for example.

Tracy Thomson, an Earth Science graduate from the University of California, USA, recently published an article in the journal Bioessays to discuss this interesting topic.

Why are there absolutely no three-legged creatures on Earth?
Meerkats stand on their tails.

Thomson shared that he got the idea to research during a lecture by paleontologist Geerat Vermeij. In it, Vermeij challenged his students to find a model of a creature that didn’t exist. And he immediately thought of animals with three limbs .

Thomson knew that some species, such as the Meerkat, stood on their hind legs and put their tails behind them for stability. The same has been observed in woodpeckers, when they use their tails against tree trunks.

Having an extra third limb to support when standing can help the creature save energy. For example, with the Meerkat and the woodpecker, they can stand without too much force. Most of the whole body can then be relaxed.

Unlike us humans, standing on two legs requires a lot of muscle groups that need to be used continuously for balance. If you try to relax as much as possible while standing, you will feel the loss of balance and fatigue of the rest of the muscle groups that are keeping you from falling.

This is a pretty popular yoga exercise, and if you’re really curious you can try it for a moment and ask: Why didn’t I grow an extra leg in the back?

Why are there absolutely no three-legged creatures on Earth?
Woodpeckers also use their tails to stand.

In fact, a third limb can not only assist in standing, but can also be useful while the animal is moving.

Thomson said he’s observed six-legged insects move in a three-legged pattern: Two lateral legs and one opposite leg lift off the ground to move forward, while the other three hold. allow the animal to stay in position.

Many animals when monkeys also use their tails to climb. While parrots also use their strong beaks to grasp and pass branches.

One of the closest models of three-legged animals that can be seen in real life are the kangaroos . The extremely strong tail can make it difficult for them to ” walk “, but is extremely supportive when they jump or move like this:

So obviously, having an extra third leg is sometimes an advantage for the creature. So why isn’t there an animal that actually has three legs? Thomson said the answer to the question probably existed millions of years ago.

Most animals develop with bilaterally symmetrical bodies,” he says. Symmetrical ” codes ” have probably been embedded in the genomes of all species since the very early stages of life’s evolution – perhaps even before the advent of creatures with legs.

And once this evolutionary trait is incorporated into the DNA, it is very difficult to remove it from the genome of an organism.

Mutations can sometimes cause creatures to have a third extra limb, such as in the case of Frank Lentini , an Italian man who lived in the late 19th and early 20th centuries. But apparently, evolution was not in favor of him. protect this mutation direction and natural selection will shut down the inheritance of those DNA, preserving the bilaterally symmetrical ” codes” .

Why are there absolutely no three-legged creatures on Earth?
Frank Lentini, an Italian three-legged man who lived in the late 19th and early 20th centuries

Since evolution has favored symmetric creatures, triplets will only exist in the human imagination. In science fiction novels or movies, aliens are sometimes built with strange shapes and walk on three legs.

They exist on planets like Enceladus, Alpha Centauri or Mars, but absolutely in real life, you will not be able to find a creature with three legs.

Thomson says imagination in this regard plays an important role. ” If we want to learn about the evolution of life, we need to understand what evolution can do and also what it can’t ,” he said.

And imagining three-legged creatures and then finding the answer to the question of why they don’t exist is not just a hobby. It deserves a real scientific study.