What the most important factor governing the addition of new foods to a baby's diet?

Ican only answer your first question, a machine is like a human body because it's a little similar. they both almost work like the same.

Behavioral science is the study of human behaviors and how they can be influenced.  by examining patterns in behavior as well as reactions, individuals with behavioral problems can be more adequately treated, resulting in greater mental health of our society/the public.