Augustine didn’t really write about evolution, since the evolution of all species was not proposed for another 1400 years. It almost sounds like he knew about it, though.
In On the Literal Meaning of Genesis (Bk. 6, ch. 5, par. 8), St. Augustine argues that Genesis chapter one says that God created male and female on the sixth day, but that Genesis chapter two says that Eve, the first woman, was not created until after God had rested on the seventh day.
His conclusion, which he had spent about 50,000 words building up to, is this:
The original creation, therefore, of the two was different from the later creation. First they were created in potency throuh the word of God and inserted seminally into the world when he created all things together, after which He rested from these works on the seventh day. From these creatures all things are made, each at its own proper time throughout the course of history. Later the man and the woman were created in accordance with God’s creative activity as it is at work through the ages and with which He works even noww, and thus it was ordained that in time Adam would be made from the slime of the earth and the woman from the side of her husband.
Here there is a chapter break, and then comes the most interesting conclusion of all:
According to the division of the works of God described above, some works belong to the invisible days in which He created all things simultaneously, and others belong to the days in which He daily fashions whatever evolves in the course of time from what I might call the primordial wrappers. (ibid. ch. 6, par. 9. Emphasis added.)
I was going to write a longer article, but Alister McGrath has both an article and a book on the subject, so I will turn this subject over to him …