Baby DNA?

Is it instinctual? Baby DNA? No one in their right mind would teach them, so they must know these things the same as they know to cry when they're hungry. They don't always know to sleep if they're tired, sometimes they just scream instead of sleep. They don't always know that you're trying to help them, or they would let you put a sweater on their little arms, or wrap them in a blanket instead of kick it off. So how do they know it? How do they know to put their head down, and push against you with their hands and feet when they want down? How do they know to raise their arms up and go slack to fall out of your arms? How do they know to bend their knees and throw themselves backward? How do they know which decibel, and which pitch, and for how long, will split your ear drums? No one has ever slapped them, so how do they know to slap you? How do they know how to spit food? No one ever modeled that for them! What are they thinking when sometimes they smile at your faces and sometimes they just stare at you? Just wondering...