A recent study led by researchers at NYU Grossman School of Medicine has uncovered a genetic change in our ancient ancestors that may provide insight into why humans lack tails, unlike monkeys. The study, published in the journal Nature, compared the DNA of tail-less apes and humans with that of tailed monkeys, revealing an insertion of DNA shared by apes and humans but absent in monkeys.

The research team focused on a gene called TBXT and found that the insertion of a DNA snippet called AluY into the gene’s regulatory code in the ancestors of apes and humans led to the loss of tails. To investigate the impact of this insertion, the team engineered mice to express both full-length and exon-skipped isoforms of the Tbxt gene, mimicking the expression pattern of its human counterpart, TBXT. The results showed that mice expressing the exon-skipped Tbxt isoform exhibited a complete absence of the tail or a shortened tail, indicating that this transcript is sufficient to induce a tail-loss phenotype.

The study’s corresponding author, Bo Xia, expressed excitement about the findings, stating that the research begins to explain how evolution removed human tails. The researchers also discovered that mice expressing the exon-skipped Tbxt isoform developed neural tube defects, affecting approximately 1 in 1,000 human neonates. This suggests that the evolution of tail loss may have been associated with an adaptive cost of potential neural tube defects, which continue to impact human health today.

The study’s findings provide a significant step forward in understanding the genetic mechanism behind the loss of tails in hominoids, shedding light on a notable anatomical change along the evolutionary lineage leading to humans and anthropomorphous apes. The research offers insights into human evolution and highlights the potential adaptive costs associated with evolutionary changes.

References

• NYU Langone Health. (2024, February 28). Change in gene code may explain how human ancestors lost tails. Phys.Org; NYU Langone Health. https://phys.org/news/2024-02-gene-code-human-ancestors-lost.html
• Xia, B., Zhang, W., Zhao, G., Zhang, X., Bai, J., Brosh, R., Wudzinska, A., Huang, E., Ashe, H., Ellis, G., Pour, M., Zhao, Y., Coelho, C., Zhu, Y., Miller, A., Dasen, J. S., Maurano, M. T., Kim, S. Y., Boeke, J. D., & Yanai, I. (2024). On the genetic basis of tail-loss evolution in humans and apes. Nature, 626(8001), 1042–1048. https://doi.org/10.1038/s41586-024-07095-8