A coworker and I reexamined a homework assignment from an ordinary differential equations textbook a number of years ago. The assignment was to develop an equation which modeled the world's population growth. Once that was developed then one could estimate the world's population at some future date. But we thought that if one could estimate the population of a future date then we could use this equation to find out the time that the world's population was 2, when the first couple arrived on the scene. The link below the next paragraph contains this result.
