Following the inception of Charles Darwin's theory of natural selection in 1838, the development of Darwin's theory to explain the "mystery of mysteries" of how new species originated was his "prime hobby" in the background to his main occupation of publishing the scientific results of the "Beagle" voyage. He was settling into married life, but suffered from bouts of illness and after his first child was born the family moved to rural Down House as a family home away from the pressures of London.