Family studies alone cannot tell us whether a trait is genetically transmitted because families share not only genes but also similar living environments.
The theory of natural selection explains the process of evolution. It maintains that inherited characteristics that give an organism a survival or reproductive advantage are passed on more often to future generations than other inherited characteristics.
This trait is not likely to be more adaptive. As far as natural selection is concerned, survival alone isn’t enough. What matters is that a person survives long enough to reproduce and pass on the trait. A person would be unable to pass on the trait regardless of whether he or she died at six or at four.
Mutations occur during the formation of egg and sperm cells, when an error occurs as DNA is being copied or when small pieces of DNA exchange places in a chromosome pair.
Adoption studies compare adopted children to their biological and adoptive parents. If the children are more similar in a trait to their biological parents than to their adoptive parents, the trait may be genetically transmitted.