Recent discoveries about the ADSL (adenylosuccinate lyase) gene, a critical enzyme involved in purine metabolism, are revealing important insights into human evolution. A new study published in Proceedings of the National Academy of Sciences (PNAS) investigates this gene’s role in distinguishing early humans from Neanderthals, shedding light on the possible evolutionary advantages it conferred. These findings, based on research involving genetically modified mice, could offer clues about why Neanderthals disappeared and why humans outcompeted them. Specifically, the gene’s interaction with brain function may have given modern humans cognitive advantages, especially when it came to tasks requiring adaptability and resource competition. Understanding this genetic difference could help clarify the survival mechanisms of early humans and highlight the biological factors behind the extinction of Neanderthals.
The Importance of ADSL: How a Single Gene Sets Us Apart
The ADSL gene, though seemingly small in its differences between humans and Neanderthals, plays a key role in purine metabolism, which is integral for DNA synthesis and energy production in cells. Researchers have noted that this gene differs between humans, Neanderthals, and other hominins, with subtle but significant effects on cognition and behavior. Unlike Neanderthals, early humans possessed a variant of ADSL that might have been linked to enhanced cognitive abilities. Such abilities are critical for problem-solving, social interaction, and survival, which may have given humans the upper hand in competing for resources. This genetic variation, while minor in terms of amino acid differences, could have had profound consequences on the survival and adaptability of Homo sapiens.
Mice Experiment: Exploring the Impact of Human-Specific ADSL
To understand the effects of the human version of ADSL, researchers introduced the gene into mice. The results were revealing: female mice expressing the human variant exhibited enhanced learning and memory abilities compared to those with the Neanderthal version of ADSL. This suggests that the human version of the gene may have offered a neurocognitive advantage, particularly in tasks requiring quick adaptation or strategic thinking. Although these findings in mice are compelling, it’s important to note that they are not directly translatable to humans due to the vast differences in neural circuitry between the species. As Xiangchun Ju, study lead author, emphasized, “It’s too early to translate these findings directly to humans, as the neural circuits of mice are vastly different.” Nonetheless, the study provides a tantalizing glimpse into how the ADSL gene could have shaped human evolution and brain function.
Female mice humanized for ADSL access water quicker after water restriction. (A) The proportion of visits by hAdsl (humanized) mice among the first 10 visits at the four corners on each day as the water was progressively restricted (12, 8, 6, 4, 3 h a day). Upper and Lower panels correspond to female and male cages (5 each). Mean ± SD across cages are shown. Green dots indicate significant differences from shuffled datasets at α = 0.05 level (two-tailed test with Bonferroni correction). A dotted horizontal line at 50% indicates equal access by hAdsl and WT (wild-type) mice. (B) The proportion of days on which hAdsl mice visited the four corners first when water became available (at 22:00). The total number of days was 9 d for each cage. (C) The percentage of days upon which hAdsl mice visited the indicated corners after water became available at 22:00. The total number of days analyzed was 14 d for each cage. (PNAS)
Evolutionary Implications: Why Neanderthals Didn’t Make It
The enhanced cognitive abilities linked to the human version of the ADSL gene may have been crucial in the survival of Homo sapiens over Neanderthals. Neanderthals, although genetically similar to humans, faced ecological and social challenges that early humans might have been better equipped to overcome. The cognitive edge provided by the ADSL variant could have made early humans more adept at navigating complex social structures and resource competition. Additionally, as the world’s climate changed and new challenges arose, those early humans equipped with this genetic advantage may have been more adaptable to shifts in their environment. This highlights a key aspect of evolutionary success: not only physical traits but also the neurological and cognitive tools that can help a species thrive in rapidly changing conditions.
Potential Pathways to Understanding Extinction
Svante Pääbo, a co-author of the study and a Nobel laureate, pointed out that “There are a small number of enzymes that were affected by evolutionary changes in the ancestors of modern humans. ADSL is one of them.” This statement underscores the importance of ADSL as a critical evolutionary adaptation. The idea that such small genetic variations could have shaped the survival of species is a compelling aspect of evolutionary theory. The human-specific variant of ADSL may have played a pivotal role in human adaptability, cognitive flexibility, and social structure, traits that might have contributed to the extinction of Neanderthals.