Evolutionism refers to the notion that basic life forms increase in complexity over time due to environmental adaptation. While commonly attributed to Charles Darwin (1809–1882), the notion that life forms vary over time had long been posited before his Origin of the Species (1859). Jean-Baptiste Lamarck’s (1744–1829) organic evolution, for instance, had posited that life forms could directly pass on traits to their progeny after environmental exposure. Though discredited today, Lamarck’s claim held widespread currency even after Mendelian genetics falsified it.