Behavioral plasticity is a change in behavior in response to internal or external stimuli. There are two general types; exogenous plasticity refers to observable changes due to outside factors such as weather, other organisms, and experiences. For instance, an initially laid-back individual who grew up in a rural community became more edgy after working in a busy city for 2 months. On the other hand, endogenous plasticity is caused by internal factors like biological clock, and heritability. For example, some people who refused to take naps when they were young children later crave naps during puberty.