The Black Death or Bubonic Plague that swept across Europe in the 14th century and had smaller outbreaks in the 15th through 17th centuries was a terrifying disease, with death rates of up to 70% within a few days of infection. Although its effects on afflicted individuals, families, and communities were horrific, it was overall economically beneficial. The Black Death normally affected overcrowded urban areas. The reduction in population did three things: it helped alleviate urban overcrowding, retarding the growth of slums, increased wages of labourers (due to the economics of scarcity), and brought about the end of serfdom. The increase in wages due to population reduction (an effect China has achieved through its 1 child policy) resulted in a dramatic improvement in the income and living conditions of the poorer classes.
This author thinks the humanism owes its existence to the plague.
"Before the plague, learning was very much in the hands of the clergy, and the focus of art, architecture, music, languages and any other form of learning was all for the glory of the Church. After the plague, secularism grew, and the questions brought about by the horror of the Black Death had opened the medieval mind to a different way of thinking. Scholars began to search elsewhere than scripture and the traditions of the Church for the keys to life, ethics, and morality; and humanism, a defining movement in the Renaissance, was born.