Anaximander saw in the world in which he lived the result of a process of evolution.

Anaximenes explains the coming into being of fire, wind, clouds, water, and earth, as due to a condensation and expansion of the universal principle, air.

The boldness of their speculations we may explain as due to a courage born of ignorance, but the explanations they offer are scientific in spirit, at least.
Moreover, these men do not stand alone.

They are the advance guard of an army whose latest representatives are the men who are enlightening the world at the present day.

The evolution of science--taking that word in the broad sense to mean organized and systematized knowledge--must be traced in the works of the Greek philosophers from Thales down.