Yeah, the aliens did it and ran away.

Missing links merely means that there's missing evidence, just because it hasn't been found it doesn't mean it doesn't exist at all. What we do know from geology is that there has some major cataclysms that have affected the landscape since we came down from the trees, what with ice ages and associated glacier melts and Biblical Deluges, comets crashing into the earth that have thrown up so much dust that had resettled again...... Huge tracts of land have been covered up including Antarctica and the tract of land between my front door and Sweden, where people are fishing and drilling for oil used to be a connected land mass. Very little evidence exists in America in particular because at one time it was many feet thick with ice.

On the other hand many cultures have myths of mankind having been created by the Gods/God, the Bible isn't unique in that and they stole it from the Sumerians. The Sumerian myths are strikingly similar to that found in the Mayan Popol Vu, and with several other cultures. The genetics for the fontal lobes looks as if it had been bolted on at a later date, which to some gives credence to alien theories. However, far more evidence suggests a global, civilised culture may have existed - Mu and Lemuria - at the time apes might have come down from the trees. Oh, not forgetting the Stoned Apes, they didn't have an issue with magic mushrooms and other hallucinogenic plants that might well have been part of their regular diet.