In a finding that could change our understanding of human evolution, recent studies revealed that modern human brains are approximately a 13% smaller than those of their ancestors from 100,000 years ago. This decline raised an intriguing question for researchers: Is it a consequence of climate change or is it related to some of the cognitive abilities we have developed?
Traditionally, the scientific community held that the “big brain” is the distinguishing characteristic of our species compared to other animals. Our ability to think and innovate allowed us to create the first artistic expressions, invent the wheel and even reach the Moon. Indeed, When compared to other animals of similar size, the human brain is gigantic. In the six million years since we shared a common ancestor with chimpanzees, the human brain has nearly quadrupled in size. However, recent studies indicate that this trend has reversed in the last 100,000 years.
A recent study led by paleoanthropologist Ian Tattersall from the American Museum of Natural History in New York traced the cranial volumes of ancient hominids. The expert found that Brain expansion occurred independently in different species and regions, including Australopithecus afarensis, Homo erectus, Homo heidelbergensis, and Homo neanderthalensis.. However, this trend was reversed with the arrival of the Homo sapienswhose brains are now 12.7% smaller than those of their ancestors from the last Ice Age.
“We have skulls of very peculiar shapes, so the first humans are very easy to recognize, and the first ones have extremely large brains”Tattersall said.
Faced with the question of how this surprising brain reduction can be explained, the paleoanthropologist maintains that the reason could be related to a change in thinking style, which he calls “symbolic information processing.” That is, think in a more abstract way to understand better. This change that Tattersall points out coincides with the invention of language, which reorganized neural pathways in a more efficient way.
According to the scientist, smaller but better organized brains were capable of performing more complex calculations, making large and expensive brains in terms of energy unnecessary.
“As smaller, better-organized brains became capable of more complex calculations, larger, metabolically expensive brains simply became unnecessary.”, Explain. “This was the time when humans began to produce symbolic artifacts and engravings with meaningful geometric images.”
However, not all scientists agree with this theory.
Jeff Morgan Stibelfrom the California Museum of Natural History, stated that the climate change might be a more plausible explanation. In his study he found that the reduction in brain size in the last 17,000 years is correlated with periods of climate warming.
“The warmer the climate, the smaller the brain size in humans, and the colder the climate, the larger the brain,” he said. He further argued that smaller brains could have been an adaptation to better dissipate heat in a warmer world.
“Nowadays, if it’s hot, we can put on a T-shirt, jump into a pool or turn on the air conditioning, but 15,000 years ago these options were not available to us,” he commented.
“He brain is the largest consumer of energy of all organs, since it weighs about 2% of our body mass, but consumes more than 20% of our metabolic energy at rest. Therefore, if the brain is a large consumer of energy and heat, it is likely to adapt to the climate as well. “Our theory is that smaller brains dissipate heat better and also have reduced heat production,” Stibel added.
Another theory suggests that brain shrinkage began with humans’ transition from being hunter-gatherers to building complex societies..
Jeremy DeSilva anthropologist at Dartmouth College, proposes that With the rise of civilizations, knowledge and tasks were divided, reducing the need for a large brain in each individual. Although this theory is also disputed, it suggests that social and cultural context plays a crucial role in brain evolution.
“The birth of complex societies and empires meant that knowledge and tasks could spread. People no longer had to know everything, and as individuals no longer had to think as much to survive, their brains shrank in size,” explained DeSilva, who analyzed skull fossils ranging from the Miocene hominid Rudapithecus (9.85 million years ago) to modern humans (300,000 to 100 years ago). After that analysis, he estimated that brains began to shrink about 3,000 years ago.
Some researchers, such as Eva Jablonka from Tel Aviv University, argued, for their part, that Factors such as poverty and malnutrition, rather than evolutionary adaptation, may have contributed to brain shrinkage.
Martha Lahr, from the University of Cambridge, adds that dependence on agriculture and nutrient deficiencies could have limited brain development in our ancestors. “Nutrient deficiency could explain the shrinkage of our skulls,” she said.
The question of whether this decrease in brain size is making us less intelligent is even more complex. Some scientists argue that while having a larger brain relative to body size generally correlates with higher intelligence, cognitive ability also depends on neural efficiency and connectivity. Although our brains are smaller, the technologies and tools we have developed allow us to offload cognitive tasks, maintaining or even enhancing our collective intelligence.
“The fact that our brain size is decreasing significantly at this time leads to the logical conclusion that our capacity for higher intelligence is reducing or at least not growing (…) However, what we have done over the last 10,000 years is to create tools and technologies that allow us to download cognition into artifacts. “We are able to store information in computers and use machines to calculate things for us,” Stibel concluded.
