Why 23andMe can't tell you everything about yourself (yet)

How can a mild-mannered grasshopper turn into a ferocious locust? Why are humans humans when we have share 80 percent of the same genetic material with a cow? In a fascinating long read at Aeon, David Dobbs delves into the differences between genetic change (evolution as you probably learned it in school) and genetic expression (the amazing powers of natural selection that scientists are only now starting to really understand).