Hormones -- such as melatonin and cortisol; the former signals the body to go to bed, while the latter signals for the sleeping person to wake up -- are created by physiological changes.
D
Punctuated equilibrium is a series of small, gradual changes over long periods of time.
Cohesion is the property of like molecules to stick to each when they have a mutual attraction
Adhesion is the property of different molecules or surfaces to stick to each other
