Modern Human Brains Have More Neurons Than Neanderthals

The field of paleoanthropology is known for its hotly contested debates, and one that has raged for decades concerns the evolutionary origin of the modern human family. One of the biggest enigmas in paleoanthropology is why our species seemed to do nothing noteworthy, or interesting for the first 300,000 years, and was not even able to cross the Red Sea and leave Africa. Then suddenly our species conquered the entire planet in only 30,000 years or so. Around 100,000 years ago, a new subspecies of humans called anatomically modern humans, or Homo sapiens sapiens, mysteriously appeared. The out-of-Africa hypothesis frequently depicts our own ancestry as a superhuman race, at the pinnacle of human evolution, the outcome of the two-million-year encephalization process of the human brain. Due to the enigmas and numerous unanswered questions surrounding our ancestors, this is very intriguing. There are important implications to the theory, though, when a pure, human race first emerges on one continent and then spreads to supplant all others. In the United States it is known as Manifest Destiny. Nonetheless, starting around 75,000 years ago, tools and weapons started to develop, becoming sharper and more resilient. As forms of artistic expression, cave paintings, jewelry, and sculptures that reveal a previously unheard of degree of sophistication and culture start to appear. Indeed, it appears as though a spark ignited the modern human brain all of a sudden. In terms of complexity, originality, and artistic and symbolic accomplishments, the spiritual belief systems of the first modern humans were far superior to those of their ancestors. Spiritual practices have evolved alongside the advancement of the human brain of early man and woman. As a result, the first modern humans experienced what has been referred to as a symbolic explosion, a significant increase in their understanding of an ability to symbolically express the spirit world. Early anthropologists thought that modern humans might have been created in the image of the gods, because they were so far ahead of everyone who came before them and the Neanderthals who were still present in the area in terms of physical and intellectual, technological, cultural, and genetic development. One of the great puzzles of human evolution is how culture suddenly appeared in such a short amount of time. The Neanderthals were probably outwitted by the rewired modern humans when they first arrived in the Levant, driving them to extinction by 40,000 years ago and leaving an enduring cultural imprint on the region. Although modern humans and Neanderthals both develop brains of comparable size, little is known about whether modern human and Neanderthal brains may have produced various numbers of neurons during development. Recent research has shown that the modern human protein TKTL1, which differs from the Neanderthal protein only by one amino acid, causes an increase in basal radial glia, a particular type of brain progenitor cell. Under a microscope, a basal radial glial cell, a kind of progenitor cell that creates neurons throughout brain development, can be seen dividing. Modern human TKTL1 increases the amount of basal radial glia and neurons, but Neanderthal TKTL1 does not. Basal radial glial cells produce the majority of the neurons in the developing neocortex, an area of the brain crucial for many cognitive functions. Because TKTL1 activity is particularly high in the frontal lobe of the fetal human brain, the researchers conclude that this single human-specific amino acid substitution in TKTL1 underlies a higher neuron production in the developing frontal lobe of the neocortex in modern humans than Neanderthals. Only a small number of proteins, or amino acids, which are the building blocks of proteins, are different between modern humans and our extinct ancestors, the Neanderthals and Denisovans. What these differences mean biologically for the development of the modern human brain is largely unknown. In actuality, the neocortex of modern humans and Neanderthals has brains that are similar in size. Some researchers believe the neural mutation hypothesis is the most cost-effective way to explain the sudden increase in brain power, though it is unclear whether this similarity in neocortex size implies a similar number of neurons. One of these proteins, called TKTL1, differs from Neanderthals by just one amino acid in almost all modern humans. Particularly, the TKTL1 of modern humans contains an arginine at the sequence position in question, whereas the TKTL1 of Neanderthals contained lysine, a related amino acid. The gene is found in neocortical progenitor cells, which develop into all cortical neurons in the developing human neocortex. Notably, the frontal lobe's progenitor cells have the highest concentration of TKTL1. The significance of these effects for the development of the human brain was then examined by the researchers. Human brain organoids, which can be created from human stem cells in cell culture dishes and mimic some aspects of early human brain development, were used to accomplish this. They substituted the lysine present in the Neanderthal gene for the arginine present in the modern human gene. The Neanderthal-type amino acid in TKTL1 was found to produce fewer basal radial glial cells than the contemporary human type, and consequently, fewer neurons. This shows that even though it is unknown how many neurons exist in the Neanderthal brain, we can assume that modern humans have more neurons than Neanderthals in the frontal lobe of the brain, which is where TKTL1 activity is greatest. The researchers also found that modern human TKTL1 affects metabolism by enhancing fatty acid synthesis, and stimulating the pentose phosphate pathway. In this way, it is hypothesized that modern human TKTL1 boosts the production of particular membrane lipids necessary for basal, radial glial cells to undergo a protracted process that stimulates their proliferation and, as a result, increases the production of neurons. These results suggest that modern humans, especially those in the frontal lobe, have a higher rate of neuronal formation in the neocortex during fetal development than did Neanderthals. It is entirely conceivable that this has improved frontal lobe-based cognitive abilities in contemporary humans. A crucial genetic mutation in the recent past led to a sudden improvement in our ancestors' brainpower. The number of brain cells in modern humans has significantly increased as a result of this mutation, according to researchers, giving them a cognitive advantage over their large-browed relatives. What specifically caused this mutation is the question. Tools and weapons began to change in shape and form beginning around 75,000 years ago, becoming sharper and more durable. The earliest modern humans were skilled hunters and warriors. Modern humans have an advantage because they have a strong sense of competition, are skilled at killing with projectile weapons from a distance, and most likely cooperated better in large groups. Cave paintings, jewelry, and sculptures that attest to an unprecedented level of culture and sophistication also begin to emerge as forms of creative expression. It seems as though the modern human brain was suddenly ignited by a spark. But the evidence suggests that this spark did not happen in the brains of our brothers and sisters, the Neanderthals and Denisovans. Interbreeding between closely related species is known in evolutionary theory as adaptive introgression, and it is not a new idea. When a species expands into a new region, it encounters a completely new set of challenges, such as a new environment, food source, predators, and infections. Natural selection, as we know it today, is the process by which advantageous spontaneous mutations gradually spread throughout the population, enabling species to adapt. However, the process is incredibly slow because these mutations don't happen very frequently. A faster solution is to breed with species that have adapted to the area and inherit some of their advantageous DNA. However, another mystery is the complete void in the modern human fossil record of Africa from the critical period between about 70,000 and 40,000 years ago. A number of genetic studies, especially those on the mitochondrial DNA, of living people indicate that modern humans evolved in sub-Saharan Africa and then left to colonize the old world. But other genetic studies, generally on nuclear DNA, argue against the African origin and exodus model, according to researchers from the Max Planck Institute for Evolutionary Anthropology. The earliest European modern human skulls from the last ice age, commonly referred to as the Cro-Magnon people, sit statistically very close to Aboriginal Australians, Papuans, and a 36,000-year-old skull from South Africa, known as the Hofma Skull. But the mysteries and issues surrounding our distant relatives have clear solutions. The history of our species evolution is a convoluted web of adaptive introgression. Thus, the most cost-effective theory to explain the unexpected rise in brain power is adaptive introgression. In comparison to those who came before or after them, the first modern humans were intellectual giants when they first appeared on the scene, they may have even been regarded as gods. The fact that these intellectual giants had indeed consumed fruit from the tree of knowledge is, however, obvious and apparent.