How does one decide who makes an “under 40” list? After the last nominations come in from staff and readers, we’re left to sort through hundreds of names, with no obvious guideposts for how to do so. Do we want the basic scientist behind a major discovery, or the executive working to translate it into medicines? The venture capitalist spinning out a half-dozen companies or the founder with one big idea? Leaders who have already brought drugs into the clinic or leaders who seem on the cusp of it?