Some human desires, appetites and instinctive responses represent evolutionary adaptations handed down to us from a long lineage of ancestors. The stoics considered humans to be rational beings who are different from animals by virtue of our ability to choose our values based upon oned assent, rather than instinct alone. Unfortunately, these natural desires can morf into desires for things that are ultimately detrimental to our physical and psychological well being. They can quickly become uncontrollable passions, obsessions, compulsions or addictions. To combat this, the stoics sought to understand human nature and to constrain human desires within reasonable boundaries so they do not become self destructive.