A Genetic Tweak Led Human Ancestors to Lose Tails 25 Million Years Ago, Study Finds
In a groundbreaking study, scientists have discovered that a single genetic tweak caused human ancestors to lose their tails approximately 25 million years ago. This genetic mutation not only led to the loss of tails but also provided evolutionary advantages such as the ability to walk upright. However, it may also be responsible for a birth defect called spina bifida that still affects babies today.
The Mystery of the Disappearing Tail
Humans’ ancestors originally possessed tails, but around 25 million years ago, they shed this appendage, leaving it to other tree-dwelling primates like monkeys. Interestingly, human fetuses start growing a tail in the womb but lose it after about eight weeks, leaving behind only the coccyx, a nub at the end of the spine where the tail used to be. Scientists have long been puzzled by the fact that humans still possess the genes to make a tail, yet our bodies refuse to do so.
Cracking the Genetic Code
Researchers at the NYU Langone and Grossman School of Medicine have finally unraveled this mystery. They discovered that a type of “jumping gene” called an Alu element played a crucial role in the loss of tails. These Alu elements are known for moving around the genome. The scientists found two Alu elements near a specific part of the TBXT gene, known as Exon 6. The insertion of these DNA sequences seemed to result in the loss of tails. To confirm their findings, the researchers inserted Alu sequences in mice and observed that some mice had shortened tails or no tails at all.
The Unanswered Questions
While this study provides valuable insights into why humans lack tails, there are still unanswered questions. Experts Miriam Konkel and Emily Casanova, who commented on the research, suggest that there may be other factors at play in tail formation that work in conjunction with the Alu elements in the TBXT gene. Nevertheless, they describe the findings as “deeply compelling” and believe they open a new chapter in understanding our evolutionary history.
The Dark Side of the Mutation
While the loss of tails brought evolutionary advantages, it also came with a cost. Scientists discovered that adding Alu sequences to the TBXT gene in mice not only truncated their tails but also led to an unusually high level of neural tube defects. In humans, this defect manifests as spina bifida, a condition where the baby’s spinal cord fails to close completely, leaving parts of the spine and nerves exposed on the back. Spina bifida can result in paralysis or incontinence and affects approximately one in 2,000 births in the US each year.
The Debate Continues
Some scientists argue that losing the tail was a necessary sacrifice for humans to walk upright. They suggest that a tail would have hindered the delicate balance required for bipedal locomotion. However, others believe it may not be that simple. Early research suggests that humans may have lost their tails while still living in trees and that the tail could have actually aided our two-legged lifestyle. These scientists propose that the mutation arose when humans’ and apes’ ancestors were isolated from other primate groups, and the loss of the tail was more of a unique trait rather than an evolutionary advantage.
In conclusion, this groundbreaking study sheds light on the genetic tweak that caused human ancestors to lose their tails millions of years ago. While it provided evolutionary advantages such as walking upright, it also led to birth defects like spina bifida. The research opens up new avenues for understanding our evolutionary history and raises intriguing questions about the role of tails in our ancestors’ lives.
