Humans are a combination of nature and nurture. Nature refers to genetics; your chromosomes (and their genes) that contain 99% of all the DNA (deoxyribonucleic acid) in your brain and body. Nurture refers to epigenetics; your cellular memories, hormones, and how they influence your chromosomes and genes. (Epigenetics sometimes can turn chromosomes on or turn chromosomes off.) If everything goes according to plan, every time your cells replace themselves or divide and multiply, the genetic information is accurately replicated. Unfortunately, this is a complex process and not as fool-proof and straightforward as one might hope.