An Essay on the Principle of Population
In the 19th century, human extinction became a popular topic in science (e.g., Thomas Robert Malthus's "An Essay on the Principle of Population") and fiction (e.g., Mary Shelley's "The Last Man"). In 1863, a few years after Charles Darwin published "On the Origin of Species", William King proposed that Neanderthals were an extinct species of the genus "Homo". At the turn of the 20th century, Russian cosmism, a precursor to modern transhumanism, advocated avoiding humanity's extinction by colonizing space.