The existence of the same mechanisms in processes as diverse as heredity and metabolism, which are the very foundations of life, can only be explained with the parenthood of all present creatures with all past living beings.
This is probably the greatest of Darwin’s ideas, and almost a century later, in 1949, the founding father of bioethics, Aldo Leopold, underlined its enormous value with this comment.
“It is a century now since Darwin gave us the first glimpse of the origin of species. We know now what was unknown to all the preceding caravan of generations: that men are only fellow-voyagers with other creatures in the odyssey of evolution. This new knowledge should have given us, by this time, a sense of kinship with fellow creatures; a wish to live and let live; a sense of wonder over the magnitude and duration of the biotic enterprise.”

The second mechanism of evolution

In Darwin’s times heredity was a mystery, but this did not prevent him from concluding that natural selection works on heritable variations. All that he needed to know about heredity were the two facts that he learned from breeders, namely that (1) every individual in a population has unique characteristics, and (2) many distinctive traits are inherited.
The discovery of the hereditary mechanism could not cancel these experimental facts, and could not therefore deny the existence of natural selection. That discovery, however, could reveal new mechanisms of evolution, and reduce the role that natural selection played in the history of life. This is why the study of heredity came to be seen as the testing ground for any evolutionary theory, and for almost a century, in fact, the debate on evolution has largely been a debate on genetics.
Modern genetics began in 1900 with the rediscovery of Mendel’s laws and with the demonstration that hereditary characters behave as discrete instructions carried by material bodies (that Wilhelm Johannsen in 1909 called “genes”).