Climate Change in Prehistoric Times May Have Contributed to the Increase in Brain Size of Human Ancestors, Study Suggests

Throughout history, human adaptations have evolved in response to various environmental factors. Anthropologists studying human evolution have suggested that climate change during prehistoric times might have influenced the body of our ancestors, especially their brain size.

Evolution of Brain Size

At Washington University in St. Louis, researchers developed a computer simulation to show the effects of mating habits and 'parental cooperation' in the survival of ancient hominins. They also investigated the contribution of the inhospitable Ice Age in speeding up the evolution of human brains.

The simulation reveals that hominins looked for partners similar to their kind due to the importance of basic necessities such as food, fire, and shelter needed to survive the harsh cold weather. These new mating habits, 'positive assortative mating,' are attributed to advanced critical human abilities, such as developing fire and language-based communication skills.

In addition, greater creativity and parents' willingness to cooperate could have contributed to our ancestors' adaptation in preventing cold-related deaths such as hypothermia. This means that the interruptions in Ice Age wars between the sexes increased the chances for intelligent parents to get along with each other and teach their children well.

Lead study author Bruce Petersen used anthropological and climate data to develop the computer simulation. He discovered that periods of severe climate change starting from a significant glacial freeze would have led to a phase of increased sexual pickiness. This period between 676,000 to 621,000 years ago may have led to 'positive assortative mating.'

The mathematical models generated by the research team found that positive assortative mating produced the fittest offspring possessing the genes needed to survive the harsh glacial freeze. It also suggests that survival pressures brought by climate change would have triggered physical changes, which had a bigger impact on natural selection.

The Future of the Human Brain

In the future, the brains of modern humans are expected to get smaller. This was revealed by a 2021 study published in Brain, Behavior, and Evolution, where the researchers identified decreasing encephalization levels in the brains of modern humans.

Study author Jeff Morgan Stibel examined the changes to the human brain using matched body remains in determining the encephalization levels across a period in human evolution. Specimens were only included if there were enough remains to generate independent estimates of body and brain mass.

Encephalization is used to represent the cognitive faculty of prehistoric humans. In mammals, increasing encephalization is believed to be the main driver of higher cognitive ability. Over the past 4 million years, the body size of hominins has increased, with the human brain growing at an inconsistent rate about the rest of the body.

The result of the study reveals that the brain mass of modern humans has been declining since 50,000 years ago. Stibel attributes these declines to human's adaptive response to changing physiology, such as obesity. Although this theory is still not proven, Stibel believes that this significant decrease in the size of the human brain will significantly affect the cognitive abilities of humans in the future.