"The basis of our evolution has always been and will be sex." Some may find this statement too radical. Why sex? Surely there are other manifestations of human nature? But, you must agree that only reproduction is the only biological purpose for which we exist. And everything else is just a means to achieve it. The ability to self-reproduce is what distinguishes living beings, for example, from stones. Human nature is universal: from continent to continent, from century to century, it remains unchanged. The nature of man, which Shakespeare described, is essentially no different from the nature of modern man, etc. Only the words have aged, but the essence has not changed.