Mammary glands are complex organs which will not produce milk until the whole complex system is complete. This involves not only the local organ, but the many supporting structures such as the pituitary gland.
The young must have been fed effectively by some other method (and if evolution were true they obviously would have survived for millions of years while the new system was evolving). Nature could not select for this system until completely developed, as the mammary glands were obviously useless until they could secrete the complex ‘miracle’ food called milk. So why did they persist in developing?
Science has now found that mother’s milk is the best food for the animals’ young. It is perfectly formulated for the mothers’ infants. Even for humans, doctors recommend mother’s milk over the best our Ph.D. nutritionists have to offer! The only satisfactory explanation for the existence of mammary glands is that they didn’t evolve, but were created.