The whole story gets more and more interesting and complex over time as we uncover it. No single "missing link." No simplistic story of homo sapiens coming in and wiping out neanderthals. A recent documentary I saw painted this very messy picture of migration in-and-out of various parts of Eurasia, back to Africa, back out and a general genetic mixing all-around. Overall modern humans out-competed neanderthals but also bred with them and that DNA shows up in many of us today.