Complex sentence: Many vegetables, such as broccoli, did not exist in the Paleolithic period; it and cabbage, cauliflower, and kale are modern cultivars of the ancient species "Brassica oleracea".
Split into simpler sentences: Many vegetables, such as broccoli, "did not... exist in the Paleolithic period". It and many other genetically similar vegetables (like cabbage, cauliflower, kale, etc.) are modern cultivars of the ancient species "Brassica oleracea".