How might behaviors affect hormones? The birdsong example demonstrates how hormones can affect behavior, but as noted, the reciprocal relation also occurs; that is, behavior can affect hormone concentrations. For example, the sight of a territorial intruder may elevate blood testosterone concentrations in resident male birds and thereby stimulate singing or fighting behavior. Similarly, male mice or rhesus monkeys that lose a fight decrease circulating testosterone concentrations for several days or even weeks afterward. Comparable results have also been reported in humans. Testosterone concentrations are affected not only in humans involved in physical combat, but also in those involved in simulated battles. For example, testosterone concentrations were elevated in winners and reduced in losers of regional chess tournaments.
Commercial synthesis came next. In the 1930s, Austrian chemists were synthesizing male and female hormones from soybean sterols (cholesterol-like substances). This process was expensive because it was hard to separate the sterols from each other. American chemist Percy Julian (1899-1975) discovered a much easier way to separate sterols, which permitted inexpensive synthesis of both progesterone and testosterone. American chemist Carl Djerassi (1923-) is also noted for synthesizing estrone and estradiol (estrogens) from plant materials.