From Early Humans to Modern Humans
One of the biggest evolutionary changes was the development of the brain. The human brain increased dramatically in size and complexity during evolution; the Smithsonian reports that brain size roughly tripled over the course of human evolution. The most rapid period of enlargement occurred approximately 800,000–200,000 years ago, when environmental conditions were highly variable. A larger and more complex brain provided greater capacity for processing information, planning and solving unfamiliar problems. Modern Homo sapiens evolved in Africa about 300,000 years ago. The average modern human brain is approximately 1,300 cubic centimeters, although brain size varies among individuals and populations.
How Much More Intelligent Are We?
It is difficult to give intelligence a simple percentage—for example, saying that modern humans are “50 times more intelligent” than early humans would not be scientifically meaningful. Intelligence is not a single measurement, and we cannot directly test the intelligence of a person who lived hundreds of thousands of years ago. However, modern humans possess an extraordinary cumulative cultural intelligence. An individual today can learn mathematics, medicine, electronics, programming, engineering and astronomy because thousands of generations have accumulated knowledge and transmitted it through language, teaching, writing and technology. This creates an important distinction:
The individual human brain may not be dramatically different in every respect from that of early Homo sapiens, but the knowledge available to a modern human is vastly greater. Our evolutionary advantage therefore comes not only from the brain itself but also from language, social cooperation, teaching, writing, institutions and technology.
Which Part of the Body Carries Our Evolutionary Memory?
There are actually two different kinds of “memory” to consider.
1. Personal memory — the brain
Your experiences, skills and memories are encoded through changes in networks of neurons and their connections. Structures including the hippocampus are particularly important for forming and retrieving certain types of memories, while memories ultimately involve distributed networks across the brain.
2. Evolutionary information — DNA
The information inherited from previous generations is carried primarily in DNA, inside cells throughout the body. DNA does not contain your grandmother’s personal memories, such as what she ate for breakfast or what she saw on a particular day. Instead, it carries genetic information that influences biological characteristics and development. Evolution therefore leaves a kind of biological history in our genome. Modern genomic research is increasingly identifying genetic changes associated with brain development, cortical organization and human cognitive traits.
The Brain’s Most Important Evolutionary Changes
The evolutionary story is not simply “a bigger brain equals greater intelligence.” The organization and connectivity of the brain also changed. The neocortex expanded substantially during human evolution and is involved in many higher cognitive functions. The prefrontal cortex is particularly important for planning, decision-making, social behavior, working with goals and other complex cognitive processes. Human brain development is also unusually prolonged. Children spend many years developing their cognitive abilities, allowing enormous amounts of information to be acquired from parents, teachers and society. Recent research is also examining the possibility that cooperative childcare and prolonged childhood played an important role in creating the conditions for human cognitive evolution. The extraordinary feature may therefore be the combination rather than any single anatomical structure. A human can learn something from another human, improve it, teach it to someone else, and have the next generation improve it again. This produces cumulative cultural evolution, allowing knowledge to grow much faster than biological evolution alone.
What Could Human Evolution Look Like in the Future?
Future human evolution is difficult to predict. Natural selection has not stopped, but the selective pressures acting on humans have changed dramatically because of medicine, technology, culture and global civilization. Future changes could involve biological adaptations to diseases, climate, diet or other environmental pressures. Genetic technologies could also eventually influence human biology, although the scientific, ethical and social consequences of deliberately modifying human genes remain substantial questions. At the same time, evolution may increasingly become intertwined with technology. Artificial intelligence, neural interfaces, biotechnology, advanced medicine and genetic engineering could change what humans can accomplish without necessarily changing the underlying human genome. The most interesting possibility is therefore not simply that humans will evolve a much larger brain. Future human capability may emerge from an increasingly close relationship between biological brains, accumulated knowledge and technology.
