In biology, a group of organisms is said to have common descent if they have a common ancestor. The most recent common ancestor is the most recent population or species which is an ancestor of all of the species being referenced, whether that be polar bears and sun bears or woolly mammoths and African elephants or even all four of those species which ancestor would most likely be one of the earliest mammal. The broadest form of common descent is universal common descent, which is the theory that all life on Earth originated from one the same common ancestor billions of years ago.
- See also: History of evolutionary thought
In 1790, Immanuel Kant (Königsberg (Kaliningrad) 1724 - 1804), in his Kritik der Urtheilskraft, states that the analogy of animal forms implies a common original type and thus a common parent.
Charles Darwin's grandfather, Erasmus Darwin, hypothesized in 1795 that all warm-blooded animals were descended from a single "living filament":
- "...would it be too bold to imagine, that all warm-blooded animals have arisen from one living filament, which THE GREAT FIRST CAUSE endued with animality...?" (Zoonomia, 1795, section 39, "Generation")
In 1859, Charles Darwin's The Origin of Species was published. The views about common descent expressed therein vary between suggesting that there was a single "first creature" to allowing that there may have been more than one. Here are the relevant quotations from the Conclusion:
- "[P]robably all of the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed."
- "The whole history of the world, as at present known, ... will hereafter be recognised as a mere fragment of time, compared with the ages which have elapsed since the first creature, the progenitor of innumerable extinct and living descendants, was created."
- "When I view all beings not as special creations, but as the lineal descendants of some few beings which lived long before the first bed of the Silurian system was deposited, they seem to me to become ennobled."
The famous closing sentence describes the "grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one." The phrase "one form" here seems to hark back to the phrase "some few beings"; in any case, the choice of words is remarkable for its consistency with recent ideas about there having been a single ancestral "genetic pool".
Evidence for common descent
Artificial selection is a great way to observe common descent; It's not natural science, but it provides observable ways to demonstrate evolution in a controlled environment. To perform artificial selection, one begins with a particular species (following examples include a wolf and wild mustard) and then they select certain characteristics for continual breed those particular characteristics. Many examples of artificial selection, like the ones below, occurred without any scientific basing.
The most obvious examples of common descent is demonstrated in the diversity found in various breed in domesticated dogs. The various breeds of dogs all share a common ancestor with the wolf but were domesticated by humans and then selectively bred in order to enhance various features such as coat color and length or body size. To see the wide range of difference between the many breeds of dogs compare the Chihuahua, Great Dane, Basset Hound, Pug, and Poodle.
Farmers have cultivated many popular vegetables from the aggressive weed, wild mustard, by artificially selecting for certain attributes. Common vegetables such as cabbage, kale, broccoli, cauliflower, kohlrabi and Brussels sprouts are all decedents of the wild mustard plant. Brussels sprouts were created by artificially selecting for large bud size. Broccoli was bred by selecting for large flower stalks. Cabbage was created by selecting for short petioles. Kale was bred by selecting for large leafs.
During Darwin's studies on the Galápagos Islands, Darwin observed 13 species of finches that are closely related and differ most markedly in the shape of their beaks. The beak of each species is suited to its preferred food, suggesting that beak shapes evolved by natural selection. Large beaks were found on the islands where the primary source of food for the finches is nuts and therefore the large beaks allowed the birds to be better equipped for opening the nuts and staying well nourished. Slender beaks were found on the finches which found insects to be the best source of food on the island they inhabited; their slender beaks allowed the birds to be better equipped for pulling out the insects from there tiny hiding places. The finch is also found on the main land and it is thought that they migrated to the islands and began adapting to their environment through natural selection.