"They knew God," that is, they experienced or were familiar with what He had done.
Rather than following truth, man rejects the knowledge of God. He willingly turns a blind eye to His creative powers, and instead, in his mind, replaces the faultless and perfect God with frail, perishable organisms: man, birds, reptiles, etc. He is willing to elevate almost anything above the true God.
And God allows this! In essence, He says, "If this is the way of life you choose, fine. Its consequences you bring upon yourselves!" The results are given in verses 24-25.
David C. Grabbe
What Evolution Really Means