Darwin, together with J. B. Lamarck, promoted a vision of a changing world, while upholding the idea that organisms evolved from a single root – a position held by Adam and Eve in the creationist worldview, and taken over in the modern era by the Last Universal Common Ancestor (LUCA). And from that remnant of the Biblical story of creation sprung the notion of a tree of life, alongside major concepts such as gradualism (the view that speciation does not occur abruptly) and the idea that minor selection pressures can, over time, have a profound effect on improved fitness.