Quote Originally Posted by Don Corleone
Aaah, but the deer did process the food for the wolf. The deer ate leaves and transformed the vegetative matter into advanced proteins. The wolf cannot do anything with the plant proteins or the carbohydrates in the leaf. The wolf relies on the deer to process the food.
The main difference is that the vegetable matter has been digested fully and transformed into materials that are being used by the deer. If the wolf was a parasite, it would never give the deer a chance to use this material to grow. The same applies to the placenta; the baby is not eating part of the mother; it is using preprocessed material that was never used by the mother.