Problem:
As far as I can determine, lactose, and the monosaccharide galactose have few biological uses outside of mammalian lactation. It not only required enzymes for its production, but enzymes in offspring for its digestion, suggesting that it serves some specific purpose. Yet intuitively, it seems like it would have been significantly easier to just concentrate glucose from the blood or generate a disaccharide readily found in the diet like sucrose, for which digestive enzymes already existed.
Question: What drove the evolution of lactose in mammalian lactation?
Explain all the points step by step.