Homo Sapiens: Genetic advantage over Neanderthals?

Homo sapiens is the only species of the human genus to have survived into the modern era. Our closest relatives, the Neanderthals, lived at the same time as our ancestors—and even interbred with them. But around 40,000 years ago, they disappeared from the Earth. The Denisovans, who lived in Siberia and were similar to the Neanderthals, died out somewhat later, but just as definitively. Why is it that only one human species was able to survive? Homo sapiens must have had an evolutionary advantage—but why exactly?

Scientists have been searching for answers to this question for decades. A key part of this research involves comparing genetic material from extinct human species with our modern-day DNA. A team from the Max Planck Institute for Evolutionary Anthropology and the Okinawa Institute of Science and Technology (OIST) in Japan has now made an important discovery. They discovered a gene mutation that may have significantly differentiated Homo sapiens from its closest relatives.

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It's only a small DNA variation found in Homo sapiens but absent from Neanderthals and Denisovans. It results in us having lower amounts of an enzyme, adenylosuccinate lyase (ADSL). To determine the significance of this mutation, the researchers implanted the altered gene in the Homo sapiens variant into laboratory mice. They then observed that not only the animals' brain metabolism changed, but also their behavior. The female mice with the altered gene were significantly more successful in gaining access to drinking water than their female counterparts.

In nature, this would be a clear survival advantage for every animal, including early humans. Did Homo sapiens prevail on Earth thanks to this mutation and displace Neanderthals and Denisovans? It is still too early to directly extrapolate the findings from animal experiments to humans, according to a press release from the OIST . However, the genetic modification could indeed have given modern humans an evolutionary advantage in certain tasks.

Exactly how the enzyme works in the brain and why it changes behavior is not yet understood. One theory is that its mutation improves signal transmission between nerve cells. Behavior is complex, the Japanese researchers write in a press release: "Finding access to water requires processing sensory information, learning which actions lead to rewards, controlling social interactions, motor planning, and many other processes. Each of these factors can involve multiple brain regions. Therefore, further studies are needed to understand the influence of ADSL on behavior."

What is known, however, is that the enzyme ADSL, which occurs in lower quantities in Homo sapiens than in earlier human species, must not become too inactive. A severe ADSL deficiency can even have a negative impact on brain performance, promoting aggressive behavior, speech disorders, and autism. The evolutionary advantage therefore appears to be that the enzyme is less active than in earlier human species. However, enough of it is present to prevent a deficiency, according to the OIST report.

According to the researchers, it has been approximately 600,000 years since Homo sapiens genetically diverged from the lineage that later gave rise to Neanderthals and Denisovans. During this period, relatively few genetic changes occurred. However, some of these must be responsible for the differences between modern humans and earlier human species.

Changes that affect the brain and behavior are the most significant, the new publication states, because they best explain why only modern humans have managed to develop rapidly changing, complex technologies and cultures.

So far, the true effects of only a few of these genetic differences have been clarified. One, for example, concerns the protein NOVA1. Researchers assume that this gene helped Homo sapiens make an evolutionary leap and develop complex language. Mice implanted with the Homo sapiens variant of this gene subsequently squeaked in more complex patterns . Another genetic mutation appears to influence cell division during brain development and led to the development of more nerve fibers in the cerebral cortex—making it more efficient.

What's clear is that there was not just one, but several genetic adaptations that helped Homo sapiens secure a survival advantage over other human species. They are still in the process of piecing the puzzle together, write the Japanese researchers, and have now found another piece with ADSL.