[Bilbo1967]

Originally Posted by WT Sharpe

.....Suppose your father or mother—let's say father for the sake of definiteness—walked into this room at the ordinary human pace of walking. And suppose just behind him was his father. And just behind him was his father. How long would we have to wait before the ancestor who enters the now-open door is a creature who normally walked on all fours? The answer is a week.
..........—Carl [Edward] Sagan (1934 – 1996), American astrophysicist and author. The Varieties of Scientific Experience: A Personal View of the Search for God (2006), Chapter 3: "The Organic Universe."

Must be a hell of a sized room