The remarkable expansion of the human brain is closely linked to a genetic difference involving a protein domain called the Olduvai domain (formerly known as DUF1220). This protein domain is encoded in multiple copies within certain genes, and humans have far more copies than other species—about 270 to nearly 290 copies on average, compared to chimpanzees with around 125 and mice with just one. This large increase in Olduvai copies is unique to humans and correlates strongly with brain size, the number of neurons in the cerebral cortex, and overall brain complexity. In other words, more copies of the Olduvai domain generally mean a bigger and more developed brain.
What does this protein domain do for us? Research indicates that Olduvai domains promote the proliferation of neural stem cells during brain development, especially in the parts of the fetal brain where most neurons are generated (such as the ventricular zones). High Olduvai copy numbers prolong the period during which neural stem cells divide and mature, resulting in more neurons being produced. This enhanced neuron production supports the growth of the neocortex—the brain region responsible for higher cognitive functions like reasoning, language, and social processing. Experiments have shown that introducing Olduvai sequences into human neural stem cells causes those cells to multiply more than usual, strengthening the link between Olduvai dosage and brain growth.
From an evolutionary and survival perspective, this genetic difference has been crucial. The expansion of the human brain endowed our ancestors with advanced cognitive abilities such as pattern recognition, problem-solving, abstract thinking, and complex communication. These traits allowed humans to innovate tools, cooperate in social groups, transmit knowledge through language, and adapt to rapidly changing environments—capabilities vital for survival and reproduction.
While a larger brain also brought greater metabolic demands and developmental complexity, the intellectual advantages shaped by Olduvai-driven brain growth have been a foundational factor enabling humans to thrive across diverse and challenging ecosystems. Thus, the Olduvai protein domain expansion forms a key genetic basis for our species’ unique cognitive capacities and long-term adaptability.
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