funny you should say that, I'm just re-reading the latter 4 books of the Holy Work. (well listening to them as audio books, which is why I started at book2 I only have the original h2g2 as the radio play).
I think HIS version was that many people regarded coming down from the trees as a mistake, and some even thought the trees had been a bad idea and think we should have stayed in the oceans.
I think my suggestion was probably first advance by a 5ft pepperpot with a gamma ray laser and a list of personality disorders as long as a whale's cock.