Although both men lived during the same time period in the nineteenth century, they did not know each other. Charles Darwin’s (1809–1882) publication On the Origin of Species (1859) popularized his theory of natural selection but raised many questions as to how organisms could display modified or new traits. In 1865 Mendel published his landmark paper “Experiments in Plant Hybridization.” Researchers have been unable to document whether either man used the other’s work in the development of their respective theories.