Proteins that help in DNA synthesis are Neanderthals and Denisovan (our closest extinct relatives) unlike modern humans, new experiments in mice are genetically modified, expressing hints from modern human versions of the art, which could have made us different.
The findings can shed light on why Neanderthals and Denisovans disappeared, researchers suggest in a new study.
However, the importance of human discoveries remains unknown.
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“It is too early to translate these findings directly into humans because the neural circuits in mice are very different,” said Xiangchun Ju, the researcher, postdoctoral researcher at the Okinawa Institute of Science and Technology in Japan, in a statement. However, this work suggests that variants found in modern humans “compete with rare resources, especially for evolutionary benefits compared to ancestral humans.”
Important proteins
Previous research found that around 600,000 years ago, modern humans diverged from their nearest evolutionary relatives, Neanderthals, Denisovan. It is not clear why modern humans survived while our closest relatives died.
To search for potential genetic clues to solve this mystery, researchers analyzed the enzyme ADSL (adenylglyconuclear lyase). This protein helps in the synthesis of purines, one of the basic components of DNA and other important molecules.
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“There are a few enzymes affected by evolutionary changes in modern ancestors. ADSL is one of them,” the statement.
ADSL is made up of a chain of 484 amino acids. This version of the enzyme, found in virtually all modern humans, differs from what is found in both Neanderthals and Denisovan with just one amino acid. The 429th amino acid in ADSL is valine in modern humans, but in our extinct relatives it is alanine.
Scientists noted that ADSL mutations are seen in modern humans, and said that they likely appeared after they were separated from the strains linked to Neanderthals and Denisovan, rather than our closest relatives. This has led researchers to investigate possible behavioral effects of this mutation.
Previous studies of lab-grown cells found that ADSL variants found in modern humans result in more unstable versions of the broken enzymes faster than those of Neanderthals and Denisovan.
Changes in behavior
A new study published on August 4th in the Journal PNAS similarly found that modern variants in mice lead to higher levels of chemicals that ADSL normally acts to synthesize purines in some organs, particularly the brain. This finding supported the idea that modern human versions of ADSL are less active than mutants found in Neanderthals and Denisovan.
In experiments where mice learnt that they can drink water following specific light or sounds, female mice genetically modified to own a version of ADSL, as well as the kinds found in modern humans, were better at getting water than littermates without this variant. This may suggest that human-like variants are motivated to learn to connect dots between water and light and sound, or to find water in some way.
The behavioral changes and ADSL levels seen in female mice carrying modern human variants of enzymes were not seen in male mice. “It is unclear why it appears that only female mice have achieved a competitive advantage,” said Izumi Fukunaga, a researcher at the Okinawa Institute of Science and Technology, in a statement. “The behavior is complicated.”
A statistical test that analyzes Neanderthal. Denisovan; and modern African, European and East Asian DNA discovered that mutations in the ASDL genes appear in the modern human genome at a higher rate than random variation over time, and that these mutations likely provided several evolutionary benefits.
Perhaps rebutting new findings, previous research has found that genetic disorders leading to ADSL deficiency in modern humans can lead to intellectual disability, language and language disorders, and other issues. This suggests that during evolution, modern humans had to balance the potential benefits of reducing ADSL activity with the problems that could arise from ADSL deficiency, said in a statement.
Meaningless
No one believes that this study will have a direct effect on why modern humans flourished or why Neanderthals and Denisovans disappeared.
These results were told Live Science by Mark Collado, a paleontologist at Simon Fraser University in Burnaby, British Columbia, who did not participate in the study.
However, strategies to use mice to study the behavioral effects of genetic differences between modern humans and our closest extinct relatives “looks very promising as a way to investigate the evolution of our brains and behaviors,” Collard said. “We hope to see a series of research like this over the next few years.”
Future research can investigate the specific mechanisms in which changes in ADSL activity affect behavior. Scientists can also explore how changes in ADSL activity are related to other behaviors and how multiple genetic changes work in concert, the study authors wrote.
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