This week, a couple of hundred venture capitalists descended on the Computer History Museum, in Mountain View, California, for Y Combinator's twice-annual Demo Day. The event showcases graduates of the famous incubator's training program to investors who hope to sniff out the next Dropbox, Airbnb, or Stripe, all of which emerged from Y Combinator. But increasingly, the entrepreneurs marching onto the stage are as likely to be experts at manipulating molecules as writing lines of code.