Saturday, April 1, 2023

How mutations made us human – DNA analysis identifies multiple episodes of genetic evolution in Homo sapiens

Irregular Evolution: The genetic basis of our humanity has evolved in many cosmic directions, as shown by comparative DNA analysis. According to this, several genetic variants important to Homo sapiens appeared 300,000 years ago. Then, about 50,000 years ago, there was another wave of genetic innovation. It primarily affects the brain and behavior and coincides with the spread of Homo sapiens in Eurasia.

At the beginning of human history, there were still many different species that existed before and from the beginning of humans. But only sane people survived and became the only human species on our planet today. but why? What made our ancestors so successful and what set them apart from their predecessors and contemporaries? To date, this question has only been partially clarified, and the genetic basis of many of the characteristics of “ordinary humans” remains partially.

Mosaic instead of linear growth

But what seems clear is that, contrary to what has long been believed, human development did not proceed in a straight line and in one direction. Alejandro Anderco of the University of Barcelona and his colleagues explain that “the anatomical features that differentiate us as a species did not appear in a bundle and in one geographic space, but gradually and evolved into a mosaic that spanned the entire African continent.” spread over.” For example, fossils show that many early humans did indeed develop parts of modern human anatomy.

Behavioral traits and mental abilities previously thought to be unique to Homo sapiens were identified by anthropologists in close relatives of our ancestors, such as Neanderthals. This includes rock art, jewelry, and funeral rituals. “The diversity of early humans surprised anthropologists,” Anderko said. On the other hand, some early Homo sapiens fossils still show ancient features.

Distinctive human genetic variant traced

But what about the genetic evolution of Homo sapiens? When did the genes that make us human and set us apart from all humans evolve? Andirko and his team have now investigated this using genome comparison. They evaluated a database for this purpose of human genetic variants that records more than 4.4 million point mutations in the genomes of people living around the world today.

From these genetic variants, the researchers mainly selected so-called high-frequency genetic variants for analysis. This region of the genome is characterized by recurrent mutations occurring only in Homo sapiens. Through comparative analysis and with the help of specialized algorithms, Andirko and his team determined when this genetic form appeared and how it relates to the chronological basis of Homo sapiens evolution.

two clear peaks of genetic innovation

Result: Our ancestors experienced two distinct episodes of genetic change – one between 300,000 years ago and another between 90,000 and 40,000 years ago. The scientist explains: “The distribution of occurrence of these high-frequency genetic variants corresponds to two periods that are very important for the evolutionary history of Homo sapiens.” “We are able to clearly identify the different eras and the variables associated with them.”

Through more detailed analysis, the team was able to identify affected functions and organs in some of these genetic variants. In addition to bones, muscles, and other physical characteristics, it also involves hormone metabolism and the brain. “We found that brain tissue specifically differed in its expression at different times in our history,” Andirko said. “So some neurodevelopmental genes are sometimes more active than others.”

From Early Humans to Homo Sapiens

The first peak of genetic variation occurred only 300,000 years ago, so around the time that Homo sapiens diverged from the rest of the human race. At that time, our ancestors developed, among other things, a straight face without a prominent jaw and other physical features of modern humans. This was proved in 2017 on Mount Irhad, Morocco. They have found the oldest Homo sapiens fossil ever found.

Also, genetic variants emerging today may give Homo sapiens new mental and behavioral abilities. Andirko and his team found evidence of this in several genetic variants from this period that promote brain tissue. Newly acquired skills may have allowed our ancestors to better cope with environmental changes.

left for the world

The second phase of a large number of new genetic variants occurred about 90,000 to 40,000 years ago. This corresponds to the stage at which Homo sapiens left Africa and began to colonize other continents. At that time, our ancestors notably developed some new mental and coordination skills, a functional analysis of genetic variants suggests. Several mutations that occurred about 50,000 years ago caused the corpus callosum, which connects the two halves of the brain, to increase dramatically in size.

A gene variant that increases gray matter volume in the cerebellum also emerged around the same time. Unlike long-term thinking, the cerebellum is not only responsible for controlling and coordinating movement, but it also plays an important role in many higher brain functions – from attention to decision making.

human gene missing

According to the research team, their findings explain how and when genetic innovation shaped the evolution of Homo sapiens. However, at the same time they also explain that the emergence of modern humans is not the result of one or more genes. “We found no evidence of evolutionary change based on one or more dominant mutations,” Andirko said.

On the contrary, many small changes and their accumulation at certain times made us who we are today. (Scientific Reports, 2022; doi:10.1038/s41598-022-13589-0)

Source: University of Barcelona

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