Humans appear to have built-in mechanisms that encourage a period of recovery after sexual satiety. Interestingly, animal studies reveal that androgen receptors (which respond to testosterone) temporarily decline with each ejaculation, suppressing libido for some period of time.
Human
A research on the relationship between ejaculation and serum testosterone level in men
Orgasmic frequency and plasma testosterone levels in normal human males
Animal
Anabolic androgens restore mating after sexual satiety in male rats
Hormonal responses to different sexually related conditions in male rats
Relationship Between Sexual Satiety and Brain Androgen Receptors
Sexual Behavior Reduces Hypothalamic Androgen Receptor Immunoreactivity