Humans and other mammals are said to have shared the same ancestor about 80 million years ago. Can the genetic pathway help chart how we have changed along the way? Or, near home, how close are we to our closest relatives, the chimpanzees, or even our closest, but extinct relatives, humans, or humans, such as Neanderthals or Denisovans? What are the differences that helped humans thrive and others perished?
We can now map the entire genome of humans, chimpanzees, or even insects and microbes. But we can’t do that with extinct species because we don’t have living tissue. The information must come from traces of DNA that we find in scraps of fossilized remains. Material samples are very small and contaminated over time and upon handling.
DNA scarcity can be dealt with by amplifying what is available, using a method that became well known during the Covid-19 virus crisis – the polymerase chain reaction (PCR) technology, in which portions of DNA are made to join or polymerize, repeatedly, in a series of Feedback, over cycles.
The first time the DNA of an extinct creature was recovered was in 1984, from a museum specimen of the koga, a zebra-like animal last seen a century ago. A few years later, using polymerase chain reaction (PCR), we were able to recover DNA from parts of 7,000-year-old soft human brain tissue found in peat bogs in Florida. PCR is a powerful tool that makes it possible to work with minimal traces, even to bones or teeth. As for contamination, new methods, such as multiple experiments and statistical analyzes, have made it possible to sequence the DNA of a series of humans that are 30,000 to 100,000 years old.
With further improvements, a draft 38,000-year-old Neanderthal genome sequence was published in 2010. Neanderthals are an extinct subspecies first identified in 1856, from bones discovered in a limestone cave in Neanderthals, a small valley in western Germany. Bones were immediately recognized as different from the bones of modern humans, but half a century passed before Neanderthals were considered a legitimate species.
Another breed of early human ancestors was the Denisovans, named after the Siberian Denisova Cave, where the remains were found. They were the bones of a young female, and in 2010, DNA was extracted from only a finger bone, using methods recognized in this year’s Nobel Prize.
“Neanderthals and Denisovans, or so-called ‘rich’ humans, shared ancestry with the ancestors of modern humans about half a million years ago,” says a research paper in the journal. science progress, authored by Dr. Svante Papu and his associates. The diagram illustrates this point at A, where modern humans are separated. According to the research paper, since an exact sequence of parts of the DNA of Neanderthals and Denisovans has been determined, it is possible to “identify the changes that characterize modern humans.
Genetic change occurs through changes in DNA. DNA is made up of millions of units, each of which is made up as a chain of only four building blocks. An accidental change in any of them would alter the DNA and the way the organism functions.
We share most of our DNA with most other organisms. But where there are differences we branched out. With our knowledge of the Neanderthal and Denisovan genomes, which constitute the last extension leading to humans, we found about a hundred cases in which a change occurred in one building block of the DNA of most humans, but not in the known parts of the DNA of Neanderthals and Denisovans. These may be signs of a genetic parting, but was the parting final?
While Neanderthals and Denisovans originated in Europe and Asia, the genetic line that came down as humans originated in Africa and became dominant. The paper says that when the breed left Africa and met a Neanderthal, there was interbreeding and some variants of Neanderthal DNA were introduced into the human gene pool. The paper says that signs of contact with Neanderthals can be detected to this day.
irritable bowel syndrome
The challenge for oxygen-dependent organisms, such as mammals, is to overcome cell damage through a reactive form of oxygen. Animals at the bottom of the evolutionary chain were able to manage it with the help of the antioxidant glutathione. Glutathione consumes reactive oxygen which preserves important cell components. Then, it is recycled with the help of an enzyme, glutathione reductase, or GR.
The research paper says that among the 100 individual genetic differences between humans and Neanderthals it is the one that influences the shape of GRs. The variant in most humans contains glycine, an amino acid that is one of the four building blocks, in the sequence that codes for GR. But Neanderthals have serine instead of glycine. As a result of gene flow from Neanderthals to humans, the Neanderthal, or ancestral form, of GR is found in a small percentage of humans, 1-2% in the Indian subcontinent and much less in Europe.
The authors say the analysis shows that the inherited form of GR is associated with circulatory disease and irritable bowel syndrome, or IBD. Both conditions are associated with oxidative stress, in which overproduction of reactive oxygen causes inflammation of the vascular membrane, and reduced availability of glutathione is a feature of IBD. GR is found in many parts of the body and oxidative stress is the cause of other diseases as well. Thus, the modern human form of GR may play a protective role in more areas than have been identified.
The paper says it’s possible that this difference in GR shape gave humans an advantage, enabling them to dominate, while the so-called archaic humans became extinct.
(The author is the founder of simplescience.in)