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: