Why do people have different traits

Despite sharing some characteristics with our peers and our family members, every one of us has a unique combination of traits.  Some traits are controlled by genes passed from parent to child, others are acquired through learning but most are influenced by a combination of genes and environmental factors

Explanation:

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.