Modern humans are evolutionary survivors and will flourish after generation while our ancient relatives die. Now, our new research in brain chemistry suggests that enzymes native to Homo Sapiens may have become more efficient water seekers than our closest extinct relatives.
About 600,000 years ago, modern humans diverged genetically from the lineage that produced Neanderthals and Denisovan. At some point after the division, an enzyme called adenylglyceae (ADSL) evolved differently in HOMO SAPIENS. In the enzyme chain of 484 amino acids, one amino acid at position 429, called alanine, was replaced by valine. It’s a small change, but I created a version of ADSL that only modern humans have.
Enzymes are important components in producing purines, which are components of DNA and RNA. If ADSL is not present in modern humans, it can lead to behavioral abnormalities such as hyperactivity and aggression. Scientists have investigated how that change in a single amino acid shapes our behavior. Their research was published in the PNAS Journal on August 4th.
“It’s exciting to uncover how small genetic changes from the ancient past helped shape the brain properties that make us human,” said Dr. Xiang-Chun Ju, a postdoctoral scholar at the Human Evolutionary Genomics Unit at the Okinawa Institute of Science and Technology in Japan.
“Studying our ancient origins is like putting together a huge puzzle, where each genetic change in our ancestors may provide clues about how our brains and behaviors evolved,” Ju told CNN via email.
Previous studies have shown that variations in ADSL in modern humans lead to less stability and less effectiveness in enzyme production. By comparison, the original version of ADSL carried by Neanderthals and Denisovans is more efficient in the synthesis of specific protein molecules. In Homo Sapiens, these molecules accumulate in organs, especially in the brain.
To learn how this affects behavior, researchers conducted experiments on mice. Some people were genetically modified to carry a less efficient version of ADSL and mimicked human ADSL. They made water available by gradually restricting access to water over the first 12 days, along with these “humanized” mice and a control group of unchanged mice, and then adding signals through the presence of sound and light. Scientists have discovered that female mice carrying human mutants of the enzyme visit the water distribution area more frequently when they are thirsty.
Perhaps scientists have hypothesized that this low version of ADSL has positively impacted access to water, increasing the competitiveness of Homo Sapiens against this important resource.
In the second study, researchers looked at the modern human genome and focused on ADSL genes that produce unique versions of the enzyme. They discovered clusters of genetic mutations carried by at least 97% of today’s humans. The location of the genes is located in an evolutionarily preferred genome region in humans, suggesting that alterations in ADSL expression continued to be passed on because it was likely that they provided some advantage to humans, the study authors reported.
“It’s really exciting to see through research like this not only identifying the genetic changes that make modern humans unique, but also understanding how these changes shape our uniqueness,” said Dr Maanatha Raghavan, assistant professor of human genetics at the University of Chicago, who was not involved in the research.
“This study raises the interesting possibility that our ancestors may have achieved advantages over contemporaries like Neanderthals and Denisovan in unstable environments with limited resources,” Raghavan said in an email.
The first complete genome of the Neanderthals was sequenced in 2010, and scientists sequenced the first Denisova genome two years later. By comparing their genetic data with modern people across Africa, Asia and Europe, scientists identify behaviors that may have helped modern people succeed while other human species disappear, researchers reported.
“Many of the changes that have happened in modern humans add to the photo of how our brains develop and function,” Ju said. “This is a step towards understanding these changes and ultimately how they work together.”
Of course, humans are not mice, and new discoveries alone cannot directly explain human behavior, said Dr. Inglida Domarchien, a senior researcher in the Department of Human and Medical Genetics at Vilnius University in Lithuania. In addition to ADSL, there are approximately 80 amino acid variants between Homo Sapiens and Neanderthals, she added.
“But this doesn’t necessarily mean that these changes defined who we are,” Domarkienė, who studied ancient DNA but was not involved in the study, told CNN via email. Rather, our amino acid variations create opportunities to combine with other conditions such as environment, intelligence, disease resistance, and social structure, shaping evolutionary success, leaving modern humans as the last surviving species of humanity.
“I believe that modern human ‘solitude’ was determined by a complex set of factors in that it is the only surviving lineage. “The results of this study bring us closer to understanding how we came here.”
According to JU, the findings raise other interesting questions about the link between ADSL and behavior. Scientists are not yet sure how the precise molecular and cellular mechanisms of ADSL form their effects on the human brain. It is unclear why experimental changes in ADSL affected behavior only in female mice.
“Can other behaviors not considered in this study also be affected by this amino acid change?” asked Ju. “Most importantly, what are the functional consequences of humans? Those are the questions we and others are trying to address now.”
Mindy Weisberger is a science writer and media producer who appeared in Live Science, Scientific American and How It Works Magazine. She is the author of “Rise of the Zombie Bugs: The Suprising Science of Savarasitic Mind-Control” (Hopkins Press).
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