Reproduction is essential for the continuation of life and the survival of each species, so it's no wonder that the human testicles pump out sperm like a wartime factory on steroids.
According to an article on Washington.edu, the average testicles of a human male are capable of producing around 1,500 sperm for every heartbeat. That's an average of 130 million sperm a day, and in four days that's as many people on the planet.
Over the period of a lifetime, the average male produces roughly 525 billion sperm cells. At least one billion of those are shed per month. Between 40 million and 1.2 billion sperm cells can be found in a single ejaculation.