Why don’t humans have tails? Scientists find answers in an unlikely place
Why don’t humans have tails?
Humans possess numerous remarkable characteristics, yet one trait commonly found in most vertebrate animals is notably absent: a tail. The reasons behind this absence have long remained enigmatic.
Tails serve various functions such as aiding in balance, propulsion, communication, and defense against insects. However, approximately 25 million years ago, humans and our closest primate relatives, the great apes, bid farewell to tails when they diverged from Old World monkeys. Although the loss of tails has been linked to our transition to bipedalism, the precise genetic factors responsible for primate taillessness have remained elusive.
Recent research has shed light on the genetic basis of our tail loss, pinpointing a brief segment of genetic code abundant in our genome that was previously disregarded as "junk DNA" – sequences seemingly devoid of biological function. Scientists identified this segment, referred to as an Alu element, within the regulatory code of the TBXT gene, which governs tail length. Alu elements belong to a category of genetic sequences known as jumping genes, capable of relocating within the genome and initiating or reversing mutations.
In the distant past, an Alu element known as AluY inserted itself into the TBXT gene of the ancestor of hominoids, which includes great apes and humans. According to a report published on February 28 in the journal Nature, scientists found that when they compared the DNA of six hominoid species with that of 15 non-hominoid primates, AluY was present exclusively in hominoid genomes. Through experiments involving genetically modified mice, a process spanning approximately four years, manipulation of Alu insertions in the TBXT genes of the rodents resulted in varying tail lengths.
Lead study author Bo Xia noted that prior to this research, numerous hypotheses existed regarding the evolutionary reasons behind taillessness in hominoids. The most prevalent theory linked the absence of tails to the development of upright posture and the evolution of bipedal locomotion.
Reference:
https://edition.cnn.com/2024/03/23/world/humans-tails-genetic-mutation-junk-dna-scn/index.html