The modification of a single gene could have caused our ancestors to lose their tails 25 million years ago. This is the conclusion of research published this Wednesday in the journal Nature, which describes for the first time a genetic mechanism that explains the anatomical change, considered key to the evolution of bipedalism among hominids.
The authors consider that the loss of the tail must have provided an enormous evolutionary advantage to our ancestors, because, in return, it increased the risk of suffering from neural tube defects, a set of congenital malformations that currently affect one in every thousand newborns. If the absence of a tail has been favored by evolution, it means that the benefits of losing it had to far outweigh the harm posed by the increased risk of suffering from these conditions.
“It is surprising that such a large anatomical change can be caused by such a small genetic change,” Itai Yanai, the researcher at Langone Health in the United States, who coordinated the work, said in an email to La Vanguardia. The authors assume, however, that other mutations had to contribute so that the loss of the tail was stabilized as a permanent trait among hominids, but this is something that will have to be confirmed in subsequent studies.
“We have wondered for a long time why hominids, including humans, do not have tails,” reflects Miriam Konkel, a researcher at Clemson University in the United States, who did not participate in the study, in statements to this medium. “This finding provides clues about how we evolve,” which we will be able to confirm and complement “as the genomes of other tailless primates become available.”
The scientists, coordinated by Tanai, analyzed in depth 140 genes that previous research had linked to tail development in vertebrates. In a remote region of one of them they identified a small segment of DNA unique to hominids. Tailed primates lack it.
The segment itself, called the Alu element, is nothing new. In fact, these types of sequences are a common trait among all primates, with and without tails. The human genome, for example, contains about a million copies of these segments spread throughout it. In many cases they have no function, but in other cases, depending on their location, they can promote large-scale changes.
In this particular case, the Alu element, located in an a priori unimportant segment of a specific gene, alters the formation of a key protein in tail development. The change is minuscule, since it does not change the components of the protein, but only its shape. However, it is enough to make the queue disappear.
To verify this, American scientists modified the genome of a group of mice in such a way that it contained the Alu element in question. The babies were born without a tail, or with a shorter appendage than usual.
Additionally, some of the mice that lost their tails developed a condition similar to spina bifida, one of the most common neural tube defects in humans. The authors conclude that losing the tail increased the risk of suffering from these malformations, a risk whose effects we may be suffering even now, 25 million years after the genetic and anatomical change.
Knowing to what extent this modification influences our current health, however, “will require many additional studies,” Bo Xia, researcher at the Broad Institute in the United States, and leader of the study, tells this medium. “For now it is difficult to know if the discovery can help prevent these conditions,” he emphasizes.
“The proposal of this type of genetic mechanisms will lead to the study of interesting questions about the development and evolution of tail loss and locomotion styles in the hominid lineage,” concludes Xia. The development of genetic sequencing techniques, which allow genomes to be analyzed with increasing quality and ease, is key to this.
