How do you know?

How do you breathe when it's all you know? How does your heart know how to beat when it's all it knows? How does a baby know how to cry when that's all it knows? How does a mother know how to give birth to a child when that's all she knows? How does father know how to protect when that's all he knows. How does an animal know how to give birth when that all they know? So once again how do you know?