Puppies are an altricial species
New born puppies and moms have a very unique biome that requires every factor to be in place to sustain the life of delicate new born puppies. Puppies require warmth from their mother to be able to digest and absorb nutrition. Puppies cannot self regulate their body temperature and because of this puppies are born as heat seeking missals. Puppies can often been seen moving their head back and forth seeking the heat of their mom. Puppies cannot maintain warmth with low blood sugar levels. A puppy that has a low blood sugar level will not be able to be warmed to a point of being able to absorb nutrition regardless of how much heat is available to the. This is a direct circle of needs that must be kept in balance.
I always laugh when someone starts asking about the temperament of the puppies at this stage. Puppies prior to six weeks of age are nearly impossible to evaluate for temperament. They still have so much development to achieve between birth and week six. Did you know that puppies cannot even pass stools or urinate on their own for the first few weeks of life? A momma dog must stimulate a puppy's bowls by licking the puppy. Some see this as keeping a puppy clean or nurturing the babies but in reality the momma is stimulating the puppy's bowls and helping them pass stools and urine. Without doing this puppies would build a toxic level of bile acids that could cause them to die.
Puppies are an altricial species they are born before they are fully developed in contrast to precocial species who can stand and walk around within hours of birth?
There is a huge social aspect to this. Precocial species are able to wander off and get lost moments after birth. It is for their protection that they imprint and bond with their mother and distrust and fear everything else. In contrast, altricial species cannot wander off for weeks or even months after birth so they will always be under the protection of their mother. They have a long and flexible social period. It is because of this that humans and dogs are able to bond so closely.
This biome must be managed perfectly to achieve all of the needs of a puppy to grow and develop past the neonatal state of being an infant.