Most theories in the 20th century argued that great leaders were born, not made. Current studies have indicated that leadership is much more complex and cannot be boiled down to a few key traits of an individual. Years of observation and study have indicated that one such trait or a set of traits does not make an extraordinary leader. What scholars have been able to arrive at is that leadership traits of an individual do not change from situation to situation; such traits include intelligence, assertiveness, or physical attractiveness.[64] However, each key trait may be applied to situations differently, depending on the circumstances. The following summarizes the main leadership traits found in research by Jon P. Howell, business professor at New Mexico State University and author of the book Snapshots of Great Leadership.