Dynamical Evolution of Planetary Systems

We seem to exist in a hazardous time,
Driftin' along here through space;
Nobody knows just when we begun,
Or how fur we've gone in the race.

Aristotle especially, both by speculation and observation... reached something like the modern idea of a succession of higher organizations from lower, and made the fruitful suggestion of "a perfecting principle" in Nature. With the coming in of Christian theology this tendency toward a yet truer theory of evolution was mainly stopped, but the old crude view remained...

Thus life by life and love by love
We passed through the cycles strange,
And breath by breath and death by death
We followed the chain of change.