If some egregious person sneakily helped himself to my last magic biscuit, bashing his head with a rock might feel warranted. If some buffoon unleashed his “domesticated” lion, running away might feel pretty darn natural.
Spurred by these simple but nightmarish thought experiments, one might conclude that our basic instincts are symptoms of a brain that evolved approximately 2.5 million years ago in what is now the African savanna. Since our minds still engage in retributive, terrified and myriad savanna-esque thoughts and actions, our brains must be mostly the same, right? This is the theory of evolutionary psychology propagated by Leda Cosmides and John Tooby of the University of California, Santa Barbara who have famously (or infamously) claimed that “our modern skulls house a Stone Age mind.”
Leading scientists have contended with this theory and have posed pointed and argumentative questions: How have humans changed neurally throughout their existence on earth? How have cultures and environments in flux reinvented and rewired the way we think?
First, some background. The genus 'homo' is at least 2.8 million years old; from this time up until about 10 thousand years ago is called the Pleistocene epoch. It was during this period, according to mitochondrial timing techniques ,which assess the rate at which mutations have accumulated in our mitochondrial genome, that humans migrated from Africa to most other areas of the world -- areas of the world that weren’t frozen, sub-zero degree wastelands.
Considering the immense 4.54 billion year history of earth, this two million year span does seem rather negligible. A meta-analysis of 63 studies that measured the strength of natural selection in 62 species, however, found that it took just 25 generations for one trait to change by one standard deviation. Additionally, scientists have estimated that at least 10 percent of the modern human genome has changed over the past 50,000 years.
But what does this illustrate about the brain? Johan Bolhuis of Utrecht University and others have countered evolutionary psychology by highlighting recent trends in neuroscience that emphasize the malleability of the human brain. Complementary to genetic changes, variations in synaptic connectivity and neural circuitry are regulated by individual experience. The brain is a remarkably plastic structure; its structural and functional organization is easily molded by the interaction between an individual and his environment. “By building homes, planting crops, and setting up social institutions,” Bolhuis suggests, “humans co-direct their own development and evolution.”
One good example of neuroplasticity is that complex process of finding meaning in inherently meaningless symbols -- the process otherwise known as reading. Invented in tandem with writing and dating back to the fourth millennium BC, reading allowed humans to share their thoughts with others articulately. Now ideas could consist of material more substantive than ambiguous grunts and vaguely obscene arm gestures.
This momentous invention rewired the brain and continues to do so today; new pathways and linked areas form at a young age during development as children begin to learn how to read. This is not an example of genetic or biologically inherited rewiring. Rather, this is an example of the brain adapting to new tools and new methods of thinking. The end result is children with neural components and circuits that did not exist millions or even hundreds of thousands of years ago.
In crude terms: Changes in brain wiring cause changes in individuals, which in turn cause changes in culture; this process occurs perpetually so until the next string of inventions.
Cultural and neural coevolution will continue to change both how humans think and act and what neural circuits underlie those processes. The prospect of a fluid and plastic mind is certainly more exciting and validated than the conviction that minds are of the “stone age.” Where might our brains be headed?
