Thursday 25 April 2024

Why humans don't have tails. Genetic basis for our tail-loss evolution.

Unlike our domestic cat companions we don't have tails. You've probably noticed! ๐Ÿ˜‰๐Ÿ˜Ž But we might have had tails and think how different the world would be if we had retained our tails like our primate cousins. The mind boggles. One's imagination can run riot with that image. All the chairs and all the sofas and all the seats on trains and buses would have to be changed.

Human with a tail in X-ray. Image by DALLE.

So what happened? Well, firstly, unlike Tucker Carlson, you've got to believe in evolution to believe in this scientific explanation. In fact, I hope Carlson reads this article because it might make him see sense about evolution. He believes that God created humans and animals under the creationist theory. He says there is no evidence for evolution which is wrong but he believes creationism about which there is certainly no evidence whatsoever. Tucker Carlson is irrational.
"It has long been speculated that tail loss in hominoids contributed to orthograde and bipedal locomotion, the evolutionary occurrence of which coincided with the loss of the tail" - quote from the study - see citation at base of page.

The reason

In summary, a genetic parasite altered a crucial gene related to tail development when our lineage diverged from other primates around 25 million years ago. This alteration ultimately led to the disappearance of tails in apes, including humans. Our tailless state owes its existence to this ancient genetic twist.

In some more detail: over millions of years, DNA undergoes changes that drive evolution. One intriguing element is the Alu element, a repetitive DNA sequence found exclusively in primates. These “jumping genes” can insert themselves randomly into the genome, potentially disrupting or enhancing gene function. In this case, the Alu elements reside in the TBXT gene, specifically within introns (DNA sequences flanking exons). Introns were once considered the “dark matter” of the genome, assumed to serve no purpose. However, when cells use the TBXT gene to generate RNA, the repetitive nature of Alu sequences causes them to bind together.

The researchers discovered two Alu elements in the TBXT gene, present in great apes but absent in monkeys. Remarkably, these elements reside in introns, not in the protein-coding exons. When RNA molecules are generated from the TBXT gene, the Alu sequences bind together, potentially influencing tail development.

Now, that is highly technical and I don't fully understand it but that is the current explanation as to why humans don't have tails. You can boil it down to the way evolution works and the way genetic mutations sometimes arise during evolution which leads to the creation of a different kind of animal and that animal does very well in terms of survival and therefore this alteration to the appearance and physiology sticks around and doesn't disappear.

Bo Xia, is the first author of the study (formerly a graduate student at New York University and now a principal investigator at the Broad Institute).

RELATED ARTICLE: Feline Evolution in Brief.

Study Citation

Xia, B., Zhang, W., Zhao, G. et al. On the genetic basis of tail-loss evolution in humans and apes. Nature 626, 1042–1048 (2024).

P.S. please forgive the occasional typo. These articles are written at breakneck speed using Dragon Dictate. I have to prepare them in around 20 mins.

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