French philosopher Rene Descartes, who lived from 1596-1650 proposed that the human mind linked people to the mind of God, but, non-humans were complex creatures without a soul, mind or reason. He believed that they couldn't feel pain or had consciousness. Charles Darwin lived between 1809-1882 and was an English naturalist. When his book On the Origin of Species was published in 1859, it created a stir because he proposed evolution from common ancestors over time. His idea that species weren't "fixed" but changed over time was very radical in its day. He placed humans in the fabric of life and not a separate part of it, and stated that "light will be thrown on the origin of man and his history." However, he wrote a book The Expression of the Emotions in Man and Animals, in 1872 that examined behavior that is genetically determined. He sought to trace the animal origins of human characteristics, such as pursing the lips in concentration or tightening eye muscles when angry. His ideas pointed to a shared human and animal ancestry, rather than divinely created human characteristics. Therefore, these two men had opposing viewpoints.