Human-Specific Molecular Features Provide Clue Behind Brain Evolution, Set Us Apart From Other Primates

In terms of size and shape, the human brain is three times bigger than a chimpanzee's and more spherical than a Neanderthal's. Neurons communicate in distinct patterns within a maze of bumps and grooves, which give us unique cognitive abilities.

These patterns are still not fully understood, but University of Texas Southwestern Medical Center experts are determined to solve the mystery that makes us human.

Human Versus Primate Brain

The brain sets modern humans apart from other primates. Humans can learn languages that chimpanzees cannot speak and learn of government and religion that do not exist in the animal kingdom.

The human brain has a type of cell that may help it adapt based on new experiences and heal from injury. There are also human neurons containing genes that affect language development. Although scientists have compared the cell types and genes in the brains of humans and other primates, they still do not have complete knowledge of their evolutionary changes.

Understanding the Complexity of Human Brain Evolution

In a new study, UT researchers compared brain cell types and activities among humans, rhesus monkeys, and chimpanzees. Genevieve Konopka has long investigated the molecular mechanisms that lead to brain disease. She believes that understanding the inner workings of the human brain could help researchers in developing treatments for conditions like Alzheimer's and schizophrenia.

Konopka's inquiry into brain evolution stemmed from her investigation of brain disease, although she could not pursue her study further because of technological limitations. In recent years, brain studies have been supported by single-cell technology, which enabled scientists to capture cells in a piece of brain tissue and study their genetic activities.

Konopka used this technology to focus on a part of the brain in the posterior cingulate cortex. This region is implicated in schizophrenia and is associated with the way humans think about themselves.

Her team compared the gene activity and oligodendrocyte amounts of human, rhesus monkey, and chimpanzee brain tissue. In a separate study, they also compared human DNA with the genetic information from Neanderthals and Denisovans.

The researchers hoped to find more oligodendrocytes in human brain tissue than chimpanzees and rhesus monkeys. Instead, they saw a human-specific increase and gene activity changes in pre-oligodendrocytes, or the brain cells that have not yet evolved to perform mature functions. Konopka concluded that the presence of these brain cells may help the human brain adapt in response to change or injury and may enable humans to continue learning into adulthood.

A gene associated with human language development was also found to have higher expression in two types of human neurons. This human-specific increase could contribute to the language of human thoughts.

Additionally, the team identified hundreds of genes that may function differently in humans, Denisovans, and Neanderthals. Such differences explain how the human brain evolved over the last 300,000 to 500,000.

What makes this research remarkable is that instead of focusing on the brain's structure, the team looked at its genetic activities. In the future, Konopka plans to use single-cell technology to investigate brain tissue from people who suffer from brain disorders such as schizophrenia.