Mind & Brain See Inside Jumping Genes in the Brain Ensure That Even Identical Twins Are Different How can identical twins grow up with different personalities? "Jumping genes" move around in neurons and alter the way they work By Fred H. Gage and Alysson R. Muotri Jean-Francois Podevin Your brain is special. So is mine. Differences arise at every level of the organ’s astonishingly intricate architecture; the human brain contains 100 billion neurons, which come in thousands of types and collectively form an estimate of more than 100 trillion interconnections. These differences, in turn, lead to variances in the ways we think, learn and behave and in our propensity for mental illness. This is only a preview. Get the rest of this article now! Select an option below: Buy Digital Issue Customer Sign In *You must have purchased this issue or have a qualifying subscription to access this content It has been identified that the institution you are trying to access this article from has institutional site license access to Scientific American on nature.com. Click here to access this article in its entirety through site license access. ADVERTISEMENT Scientific American is a trademark of Scientific American, Inc., used with permission © 2015 Scientific American, a Division of Nature America, Inc. All Rights Reserved.