Big Brains

Human brains (circa 1500 cc) are much bigger than those of a Gorilla (circa 500cc) or a Chimpanzee (circa 400cc). A Cambridge University study examined how this size differential comes about (https://www.theguardian.com/science/2021/mar/24/scientists-discover-why-the-human-brain-is-so-big). The study involved scientists taking material (left over from operations) from these 3 Primate species. The samples were converted into stem cells (cells with a capacity to develop into a variety of tissue types). The cultured stem cells were then grown and given the necessary stimuli to develop into tiny brain organoids. The size differences were caused by a genetic switch (Zeb2), which was activated later in the case of the human material. This caused the cells to divide more, as the tissue matured, so the human brain organoids were eventually bigger. It is possible this mechanism is a solution to a biological quandary. It pays humans to have big brains. If they were too large at birth, however, passage through the female's birth canal would be extremely hazardous (to both baby and mother). Switching Zeb2 on after parturition, would be a way around the problem.