section_path: Evolution of lactation
section_name: Evolution of lactation
paragraph_text: Evolution of lactation
  
  The mammary gland is thought to have derived from apocrine skin glands. It has been suggested that the original function of lactation (milk production) was keeping eggs moist. Much of the argument is based on monotremes (egg-laying mammals). The original adaptive significance of milk secretions may have been nutrition and immunological protection.
  
  Tritylodontid cynodonts seem to have displayed lactation, based on their dental replacement patterns.