In each question, the first and the last sentences of the passage are numbered S1 and S6 respectively. The rest of the passage is split into four parts. These four sentences are jumbled. Read the sentences and identify their correct and logical order.

---

S1: Our ancestors thought that anything which moved itself was alive.
P : The philosopher Descartes thought that both men and animals were machines.
Q : But a machine such as a motorcar or a steamship moves itself, as soon as machines which moved themselves had been made, people asked "Is man a machine?"
R : And before the days of machinery that was a good definition.
S : He also thought that the human machine was partly controlled by the soul action on a certain part of the brain, while animals had no souls.
S6: Therefore some scientists think that life is just a very complicated mechanism.
The Proper sequence should be: