I’m being frank in my answer: Humans haven’t lost their tails since we never had them. Also, there will be no point in talking about something if it is owned and lost. because and much less for what.

Its original function was to propel itself through the aquatic environment.

Surprising to some, the tail is one of the five major features of chordates, and therefore vertebrates. It is the elongation of the posterior end of the body and its beginning is just behind the anus.

When the vertebrae emerged, the tail (it was only an extension of the notochord, spinal cord and musculature in the postal region) was reinforced by the end of the vertebral column, the caudal vertebra. Its function, although more efficient, continued to be to advance movement in the aquatic environment. Right now, we can appreciate it in the typical undulation of a swimming shark.

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Difficulty getting out of the water

The anatomical and physiological revolution that led to the conquest of the terrestrial environment also included the tail. First of all, for the most obvious: the tail no longer advances the movement, the legs do. But there is another, much more interesting hidden aspect. Gravity is a problem when we wish not to live dragging ourselves, as we do not have the force of repulsion against the force of gravity (as occurs in a dense medium such as water).

“Lifting” the body was a complex task, but evolutionary innovations adapted biological designs, leaving the most competent road, canal, and port engineers speechless. In fact, a skeletal morphology very similar to Forth bridges emerged: the trunk would hang between two pairs of legs. columns), muscles and ligaments (elastic and flexible) resist tensions, and bones (hard and rigid) resist compressions.

It was very important to avoid flattening and adopt the curved shape to support the weight. For this reason, and as in suspension arch bridges, the arched column form was chosen. But a new problem has arisen: our wonderful biological bridge it cannot be static as an animal has to move. had to be one mobile bridge here the tail will play a key role, heading towards the opposite side where the support is made. Thus, overloads are prevented by acting as a counterweight that oscillates to the right and left.

Even more interesting was his role in reptiles that rose up to their feet. Bipedalism of dinosaurs like that of iguanodontid ouranosaursBiomechanically, a child is nothing more than a seesaw with the tail against the weight of the front half of the body. The balance point will be the hips.

More amazing queue features

The tail also serves as a “third support”, which we appreciate in bipedal mammals such as kangaroos, contributing to reptiles’ increased standing efficiency. At rest, the legs and tail form a tripod that guarantees perfect balance.

In addition to these basic qualities, the tail can interfere with a wide variety of functions such as defense, predation, sexual attraction, food reserve, flight direction control (in birds), social communication, thermal care, and even situational. Arboreal species with pioneer tails, suspension, and branch-to-branch movement.

Everyone agrees, then, that the tail is a tremendous morphological invention. So why have we given up on this highly plastic and multifunctional biological tool?

We humans didn’t lose our tails, we never had them

The evolutionary line that gave rise to the hominids was characterized by three major transitions relative to the axial skeleton: tail loss and adaptation to orthograde (upright) stance, and bipedal locomotion.

But these three big changes did not happen at the same time. In fact, tail loss occurred in a pronograde (movement supported by four limbs) context, and this is how gorillas and chimpanzees move without showing a tail. Its loss, then, is an evolutionary phenomenon independent of upright posture and occurred before the first hominin appeared.

In other words, we humans didn’t lose our tails because tails disappeared long before we appeared in our evolutionary lineage.

On the other hand, and as Xia et al recently published, the tail has largely disappeared. It was simply due to a mutation consisting of the addition of an Alu element to the genome of our hominid ancestors (Alu sequences are motile non-coding DNA fragments associated with different evolutionary processes of primates). They demonstrated this easily and simply by inserting the Alu sequence into an intron of the TBXT gene of mice, and surprisingly, the little mice were born tailless.

Finally, it should be noted that mutations are random, that is, there are no mutations. because. They just happen to be, and if they don’t affect the fitness of the species, they’re not negatively selected, they’re not beheaded by natural selection, and keep moving forward. No finalism, so for whatnor any path followed excellence nothing preset. In fact, Alu additions have been associated with several inherited diseases in humans such as hemophilia A and B, familial hypercholesterolemia, neurofibromatosis type 1 or hereditary colon cancer.

Given all this, unfortunately we have no queue! To the wonderful functional applications we have commented on, we must add what it means to avoid these pathological risk factors driven by Alu arrays. What he really misses, though more than one, is the idea of ​​having a bright and sensual tail, acting thought-provoking and captivating those who think. with ties, piercing or simply, with a brightly fluffy pom-pom… What a powerful weapon of seduction we humans have missed!

A. Victoria de Andrés Fernández, professor in the Department of Animal Biology, University of Malaga

This article was originally published on The Conversation. Read the original.