Modern humans have a unique evolutionary story. While our ancient relatives like Neanderthals and Denisovans disappeared, we thrived. Recent research suggests a special enzyme in our brains may explain why we became more adept at finding water.
About 600,000 years ago, modern humans branched off from the lineage that gave rise to Neanderthals and Denisovans. During this time, a specific enzyme, adenylosuccinate lyase (ADSL), developed differently in Homo sapiens. A tiny change in its makeup—one amino acid swapping from alanine to valine—set us apart. This modification created a unique type of ADSL found only in our species.
This enzyme plays a crucial role in producing purine, a fundamental component of DNA and RNA. Missing ADSL can lead to behavioral issues like hyperactivity. Researchers explored how this single amino acid change might influence our behavior, and their findings were published in the journal PNAS.
“Understanding how small genetic tweaks from our past shaped what makes us human is thrilling,” said Dr. Xiang-Chun Ju, the lead author of the study. He emphasizes that studying our origins is like piecing together a puzzle. Every genetic shift may shed light on how our brains and behaviors formed.
Previously, it was thought that this specific ADSL version in modern humans is less stable and efficient than that of our extinct relatives. The Neanderthal version is more effective at creating certain proteins, while in Homo sapiens, these proteins gather, especially in the brain.
To explore the effects of ADSL on behavior, researchers conducted experiments using mice. Some had a modified version of ADSL that mimicked humans. After restricting their water access, the “humanized” mice tended to seek out water more frequently than their unaltered counterparts. This suggests that our enzyme might help modern humans compete better for vital water resources.
The researchers also analyzed the modern human genome and found several variants associated with ADSL that are common in 97% of today’s humans. These could make ADSL even less effective, indicating that this mutation likely provided some evolutionary advantage.
Dr. Maanasa Raghavan, a human genetics expert at the University of Chicago, noted that the study hints at how our ancestors might have gained the upper hand over Neanderthals and Denisovans during hard times. She remarked, “We’re moving from identifying genetic differences to understanding how they shape us as a species.”
In 2010, the first complete Neanderthal genome was sequenced, followed by the Denisovan genome two years later. By examining genetic data from modern humans across the globe, scientists aim to understand the factors that allowed us to survive while other hominins went extinct. Ju added, “These changes influence how our brains develop and function.”
While these discoveries are groundbreaking, it’s important to remember that humans are not mice. Dr. Ingrida Domarkienė from Vilnius University pointed out that the study alone cannot fully explain human behavior, as there are numerous amino acid differences between Homo sapiens and Neanderthals. She noted, “It’s a complex mix of genetic, environmental, and social factors that shaped our evolutionary journey.”
Domarkienė emphasized the uncertainty surrounding how these findings could link ADSL to specific human behaviors. Future research aims to address these questions and further explore the consequences of these genetic changes.
