Underlying the significant differences in brain — to say nothing of the vast difference in mind — is a genetic mystery… :
The Smithsonian National Museum of Natural History tells us that “While the genetic difference between individual humans today is minuscule – about 0.1%, on average – study of the same aspects of the chimpanzee genome indicates a difference of about 1.2%. The bonobo (Pan paniscus), which is the close cousin of chimpanzees (Pan troglodytes), differs from humans to the same degree. The DNA difference with gorillas, another of the African apes, is about 1.6%. Most importantly, chimpanzees, bonobos, and humans all show this same amount of difference from gorillas. A difference of 3.1% distinguishes us and the African apes from the Asian great ape, the orangutan.” (August 15, 2022)
The differences between our brains and those of primates seem to be much greater than the genetic differences, so they don’t seem to originate in the genes. The mystery is perhaps analogous to that of the human mind.News, “Researchers find more ways that human and ape brains differ” at Mind Matters News
Takehome: The differences between human brains and other primate brains seem greater than the 1.2% – 1.6% genetic difference the Smithsonian posits for humans vs. apes.
You may also wish to read: Your mind vs. your brain: Ten things to know