Why Don’t Humans have Tails? Scientists Find Answers in an Unlikely Place

A common feature amongst most animals with backbones is a tail, something that humans lack. This has been mystery and questioned by many. In animals with tails, they are used for balance, propulsion, communication, and defense against biting insects. About 25 million years ago, primates said goodbye to the tails when they split from Old World monkeys. They no longer had a use for the tail. Our transition to bipedalism was thought to be connected to the loss of our tails, but we hadn’t known the genetics behind it. 

Now researchers have found new information that changes the trajectory of our thinking. They have found that our tail loss was due to a short sequence of genetic code that is abundant in our genome but was seen as junk DNA. Junk DNA is a sequence that serves no biological purpose for us. The identified snippet is an Alu element which is in the regulatory code of a gene associated with tail length called TBXT. Alu can switch their location in the genome which can trigger or undo mutations. At some point the Alu jumped into the TBXT gene in great apes and humans. Evolution is an interesting topic because it explains a lot of the world around us today. It was interesting to learn how we evolved to have no tail and how it no longer became any use to us. 

Main Article: https://www.cnn.com/2024/03/23/world/humans-tails-genetic-mutation-junk-dna-scn/index.html

2nd Link: https://www.nature.com/articles/s41586-024-07095-8 

Our Genetic Basis of Endurance Running

Humans have been long heralded for their ability to run for long distances, an ability that separates us from other mammalian species. As we learned from biodiversity and evolution, several key structural changes of early hominid species led to the development of humans being able to walk and run upright with ease. Some of these changes include: angled femoral bone head, s-shaped spine, and placement of foramen magnum directly under the skull. Although these structural changes have aided humans greatly in efficiently traveling on two legs, not much is known about the genetic mechanism of our endurance prowess. Not until a study done by Okerblom et al., did a genetic link to our long distance running ability was found.

The researchers pinpointed a mutated gene that they believed served as a catalyst to running, called CMAH, whose mutation coincided with a change in lifestyle from more primate to more human (2-3mya). Current mutations in CMAH have been most commonly linked with several disorders, such as muscular dystrophy and diabetes, however, Okerblom et al. hoped to shed light on the positives of this gene with their study. To conduct their study, the researchers utilized two groups of mice, one with and the other without mutations in the CMAH gene. To test the effects of mutation in this gene on endurance, they had the two groups of mice run on a small treadmill for a period of time. What they found was that the mice with the mutated version of the gene ran faster and further than the mice without mutations.

With the results of this study, Okerblom et al. sought to find the genetic basis of human's ability to run for long distances. Although several professionals advise caution in making an immediate link with the mutated CMAH gene to increased endurance, it is a promising step forward in finding an answer to our history of endurance.

As a distance runner myself, I often marvel at some of the athletic feats of elite distance runners when they smash a record at a certain distance. The record breaking marathon ran recently by Eliud Kipchoge at Berlin, for example, is one of the most impressive endurance feats I can think of. Eliud nearly clocked a sub two hour marathon, for a 4:38 average for each mile, which is faster than most of us can run for one. Eliud has been close to breaking two hours at this distance, which has long been thought to be impossible. That makes me wonder if he, in fact, carries a mutated version of the CMAH gene.

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