The human brain is a big deal. In relation to body size, it’s nearly six times bigger than that of other placental mammals. Our brains’ size and organizational complexity are hallmarks of being human.
But what were the genetic changes behind our big, complex brains, and what drove their evolution? Key new evidence, and a new model, move us closer to finally figuring it out.
How to Build a Brain
In May, a pair of papers published by separate teams in the journal Cell focused on the NOTCH family of genes, found in all animals and critical to an embryo’s development: They produce the proteins that tell stem cells what to turn into, such as neurons in the brain. The researchers looked at relatives of the NOTCH2 gene that are present today only in humans.
In a distant ancestor 8 million to 14 million years ago, they found, a copying error resulted in an “extra hunk of DNA,” says David Haussler of the University of California, Santa Cruz, a senior author of one of the new studies.
