Full Idea
Nothing which lacks life and reason can produce from itself something which is alive and rational; but the cosmos can produce from itself things which are alive and rational; therefore the cosmos is alive and rational.
Gist of Idea
Since the cosmos produces what is alive and rational, it too must be alive and rational
Source
Zeno (Citium) (fragments/reports [c.294 BCE]), quoted by M. Tullius Cicero - On the Nature of the Gods ('De natura deorum') 2.22
Book Reference
'The Stoics Reader', ed/tr. Inwood,B/Gerson,L.P. [Hackett 2008], p.63
A Reaction
Eggs and sperm don't seem to be rational, but I don't suppose they count. I note that this is presented as a formal proof, when actually it is just an evaluation of evidence. Logic as rhetoric, I would say.