Friedrich Nietzsche & Friedrich Nietzsche 
The Joyful Wisdom [EPUB ebook] 

Whether I look with a good or an evil eye upon men, I find them always at one problem, each and all of them: to do that which conduces to the conservation of the human species. And certainly not out of any sentiment of love for this species, but simply because nothing in them is older, stronger, more inexorable, and more unconquerable than that instinct, —because it is precisely the essence of our race and herd.