Summary: A study examines how the human brain evolved and the impacts of having many cortical neurons on development, lifespan and culture.
Source: The Conversation
Give thanks—for the brain that made us who we are
As you sit at the dinner table, consider one of the deeper gifts of our evolutionary past: the long, complex journey that produced our unusually large brain and extended lifespan. Thanks to advances mounted over millions of years—most notably the invention of cooking—humans developed a cortex with a uniquely high number of neurons. Those neurons underlie prolonged childhoods, multi-generational learning, richer cultures and the ability to create technologies that connect people across the globe.
These biological and cultural legacies mean four generations can gather around a meal to trade stories, teach, and practice the delicate art of what to say and what to keep quiet. As our brains grew denser with neurons, so did our capacity to accumulate knowledge and to pass it on, fueling the long arc of human culture.
Brains are made of cells—how many, exactly?
For decades, popular claims and even some textbooks circulated catchy but misleading statements—like the idea we use only 10% of our brains or that the brain is composed of a fixed “100 billion neurons and ten times as many glial cells.” Those round numbers concealed uncertainty: neuroscientists had rough estimates but lacked a reliable, rapid method to count cells accurately across species.
Work developed to fill that gap changed the picture. Using a method that turned brain tissue into a homogeneous sample for microscopic counting, researchers were finally able to produce consistent, reproducible cell counts. These measurements revealed important differences across animal groups and brought precision to statements about how many neurons reside where in the brain.
Different brains, different building blocks
Not all large brains are composed the same way. The number of neurons—and where they sit—matters more than overall brain size. Primates, including humans, pack more neurons into the cerebral cortex than most other mammals of similar size. Some species, such as elephants, have large brains but relatively few, very large neurons. Birds can have very small brains that nonetheless contain many tiny neurons, supporting complex behaviors despite modest size.
The cerebral cortex is especially important because it supports higher-order cognition: planning, memory, abstract thinking and learning. Neurons are the “Lego pieces” of cognition, so the more cortical neurons a species has, the greater its potential behavioral flexibility and cognitive complexity.
Researchers have also found consistent relationships linking cortical neuron number with life-history traits: species with more cortical neurons typically take longer to reach maturity and tend to live longer. In other words, acquiring many cortical neurons appears to come with both an extended developmental period and an extended lifespan—time to learn and time to use what is learned.
Fueling a big brain
More neurons require more energy. If early humans had continued to eat only raw food like other primates, they would have needed to spend the majority of each day foraging and chewing to meet the caloric demands of a neuron-rich brain—time that would have left little room for other activities that drive cultural and technological progress.
Two key innovations changed that constraint. Stone tools and, crucially, controlled use of fire made food easier and faster to digest. Cooking increased the caloric return from the same food, dramatically reducing the time needed for feeding and freeing energy and hours for social interaction, tool-making and knowledge transmission.
With more reliable energy intake, successive human generations could grow larger, denser cortices. As brains accumulated cortical neurons, children remained dependent longer, parents and grandparents lived longer, and intergenerational learning became more powerful. Culture grew more complex and durable: technologies, stories, scientific knowledge and institutions could be retained and refined across generations.
What makes us modern
Our biology—being born with many cortical neurons—creates the potential for long, slow development and extended lifespans that support deep cultural transmission. But modern humanity is as much about culture as it is about anatomy. The combination of neuron-rich brains, energy-saving technologies like cooking, and social structures that encourage teaching and storytelling produced the uniquely human capacity to accumulate and transmit cultural knowledge.
We remain modern humans so long as we value gathering together, sharing lessons learned, celebrating differences, and continuing to pass wisdom from one generation to the next.
Source: The Conversation
Media contact: Suzana Herculano-Houzel – The Conversation
Image source: Image adapted from the original news release.