The gene which differs between humans and Neanderthals could shed light on the disappearance of the species, suggests the study of the mouse
A protein that helps to synthesize DNA is different in modern humans than in Neanderthals and Denisovans – our most extinct parents – and new experiences on the genetically modified mouse to express the modern human version indicates that this may have made us behave differently.
This discovery, in turn, could shed light on the reasons why Neanderthals and Denisovans have disappeared, researchers offer in a new study.
But the meaning of the results for humans is not yet clear.
“It is too early to translate these results directly into humans, because the neural circuits of the mice are very different”, the main author of the study, Xiangchun JuPostdoctoral researcher at the Okinawa Institute of Sciences and Technology in Japan, said in a press release. However, this work suggests that the variant observed in modern humans “could have given us an evolutionary advantage in particular tasks compared to ancestral humans”, such as competition for rare resources.
Key protein
Previous research has revealed that modern humans diverge from their evolutionary parents, their nearest neanderthals and Denisovans, About 600,000 years ago. We do not know why modern humans have survived while our nearest parents died.
To seek potential genetic indices to resolve this mystery, the researchers analyzed the ADSL (Lyase adénylosuccinate) enzyme. This protein helps to synthesize the purine, one of the fundamental constituent elements of DNA and other vital molecules.
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“There are a small number of enzymes that have been affected by evolutionary changes in ancestors of modern humans. ADSL is one of them”, co-author of the study Svante Pääbo,, Nobel Prize winnersaid a press release from the Okinawa Institute for Japan Sciences and Technology, and director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, in a statement.
ADSL is made up of a chain of 484 amino acids. The version of this enzyme found in virtually all modern humans differs from that observed in Neanderthals and Denisovans by a single amino acid – 429th Amino in ADSL is valine in modern man but alanine in our extinct parents.
Scientists noted that the ADSL mutation is observed in modern humans and not our nearest parents, and therefore probably appeared after our separation from the line that led to Neanderthals and Denisovans. This led researchers to study the possible behavioral effects of this mutation.
Previous research on laboratory cultivated cells has revealed that the ADSL variant observed in modern humans resulted in a more unstable version of the enzyme which fell faster compared to that of Neanderthals and Denisovans.
Behavior changes
The new study, published on August 4 in the journal PNALikewise, I found that, in mice, the modern variant leads to higher levels of chemicals on which ADSL acts normally to synthesize the purine in several organs, in particular the brain. This observation argued that the modern human version of ADSL is less active than the variant observed in Neanderthals and Denisovans.
In the experiments where the mice learned that they could have a glass of water according to specific lights or sounds, the genetically modified female mice to have a version of ADSL similar to that observed in modern humans were better to obtain water than their litter without this variant. This could suggest that the human variant has made female mice better to learn to connect the points between water and lights or sounds, or more motivated to search for water in one way or another.
The behavioral changes and the ADSL levels observed in female mice with the modern human variant of the enzyme have not been observed in male mice. “We do not know why only female mice seemed to gain a competitive advantage”, co-author of the study Izumi FukunagaA researcher at the Okinawa Institute in Sciences and Technology, said in a statement. “The behavior is complex.”
Statistical tests analyzing the Neanderthal; Denisovan; And African, European and modern DNA in Eastern Modern has found that the mutations of the ASDL gene appeared in modern human genomes at higher rates than random variations over time, which makes it likely that these changes provide a certain evolutionary advantage.
Perhaps by running against new discoveries, previous work has revealed that genetic disorders leading to an ADSL deficiency in modern man can lead to intellectual disability, a disability of speech and language and other problems. This suggests that during evolution, modern humans had to balance the potential advantages of reducing ADSL activity with the problems that could arise from an ADSL deficiency, co-author of the study Shin-yu leeAlso of the Okinawa Institute of Sciences and Technology, said in a statement.
Unclear implications
Not everyone thinks that the study has direct implications to explain why modern humans have prospered or why Neanderthals or Denisovans have disappeared.
These results on mice “do not say too much about human evolution at this stage”, ” Mark CollardPaleoanthropologist at Simon Fraser University in Burnaby, British Columbia, who did not participate in this research, said in Live Science.
However, the strategy for using mice to study the behavioral effects of genetic differences between modern humans and our closest parents “seems very promising as a means of studying the evolution of our brain and our behavior,” said Collard. “I expect that we will see a waterfall like this in the coming years.”
Future research can study the specific mechanisms by which changes in ADSL activity influence behavior. Scientists can also explore how changes in ADSL activity are associated with other behaviors and how multiple genetic changes could work in concert, study authors wrote.
