Men act the way they do as a result of their testosterone levels. High and low levels of this hormone influence sex drive, depression, aggression, stress, anxiety and a variety of other behaviors in men.
Testosterone regulates sperm production, promotes muscle mass, determines energy levels, and even defines physical signs of manhood, such as facial hair, voice changes and bone structure. At a behavioral level, testosterone hormones, or androgen hormones, are at their highest during puberty through early adulthood. This explains why men may be more sexually active during those years and exhibit territorial behavior with other men by fighting or playing athletic sports to compete for the women in their social circles.
After age 30, testosterone levels decrease about 1 percent per year of life, according to Healthline. While men are biologically charged to impress women, they later use the tempered testosterone levels to process stress from family life and career goals.
Too low of testosterone levels, however, may result in depression, low sex drive, infertility and lack of energy. On the other hand, age-appropriate levels of testosterone result in men who pursue women in their youth and pursue ways to sustain a livelihood for a family in later years. Testosterone levels also contribute to some stereotypical behavior, such as feeling anxious over calling a girl's number or focusing on sex and work more than romantic gestures.