some points from the documentary
"Why Dogs Smile and Chimpanzees Cry" (1999)

for millions of years reptiles ruled the land. when the land suddenly started changing, it was the ability of the mammalian brain to adapt that made them win over the reptiles during those troubled times.

mammals learned from each other and lived in groups. the mammals possessed "motherly love" and took care of their young. baby reptiles are ignored by their mother and do not learn from them and only have basic survival emotion such as fear.

mammals must learn what is not pre-programmed in them. this is the key to their adaptation. this learning takes time and is why the more complex species take longer to develop into adulthood. they learn what to fear and how to behave. mothers punish to teach what is dangerous.

maternal love is addictive. it produces a good feeling. physical touch is vital in the healthy development of the young. holding, hugging, and playing are needed. play is essential for development and it practices future skills that will be needed.

the brain is like an onion. we have the ancient reptile brain at the core which gives us basic survival ability and fear. after that there is the more developed area which gives us motherhood and basic learning. the outer part of the brain is the area that allows for complex social learning.