"The Consilience of Inductions takes place when an Induction, obtained from one class of facts, coincides with an Induction obtained from another different class. Thus Consilience is a test of the truth of the Theory in which it occurs."
--William Whewell, 1840.
Consilience is a very useful way to evaluate theories of science and any sort, but it is not very well known. When one theory has many independent lines of evidence, then it is the best theory to accept. It is inappropriate to think that there could be one single "smoking gun," although that is what most people really want in terms of evidence.
It is the true theory that has on its side many diverse lines of evidence. It is the untrue theory that dismisses each line of evidence, finding ad hoc explanations with weak evidence for each. That is the method of pseudoscience adherents, conspiracy theorists, ideologues and representatives of scientific theories that are just plain wrong.
As just one example, let us look at a fossil of one transitional species, the Archaeopteryx.
This species was found just two years after Darwin published in book. It is a bird with teeth, clawed wings, long bony tail, thick bones, and a spinal chord that connects at the back of the skull instead of the bottom. This seems to fit an evolutionary link between birds and dinosaurs, and the link is reinforced by fossils of feathered dinosaurs.
What do creationists say about the Archaeopteryx? Well, many things. Answers In Genesis wrote a long article and put it online, refuting the evolutionary link between dinosaurs and birds.
Evolutionists disagree about whether birds evolved from theropod dinosaurs or from another branch of archosauria.
Birds are warm-blooded, and dinosaurs are cold-blooded.
Bird-hipped dinosaurs are even less bird-like than lizard-hipped dinosaurs in most respects.
In embryological development, the three fingers retained in theropod dinosaurs are fingers 1, 2, and 3 while the fingers retained in birds are 2, 3, and 4.
The theropod Sinosauropteryx had lung and respiratory mechanics similar to that of a crocodile and not a bird.
Fossil "protofeathers" on some dinosaurs are actually connective tissue fibers.
Feathers and scales are dissimilar.
Feathers on dinosaurs are not enough to prove a transition. It would take a "scale-feather."
Archaeopteryx is older than the “feathered” dinosaurs.
"For many years Archaeopteryx has been touted in biology textbooks and museums as the perfect transitional fossil, presumably being precisely intermediate between reptiles and birds. Much has been made over the fact that Archaeopteryx had teeth, fingers on its wings, and a long tail—all supposedly proving its reptilian ancestry. While there are no living birds with teeth, other fossilized birds such as Hesperornis also had teeth. Some modern birds, such as the ostrich, have fingers on their wings, and the juvenile hoatzin (a South American bird) has well-developed fingers and toes with which it can climb trees."
The theropod type of dinosaur that is believed to have evolved into flying birds is poorly designed for flight because of its short forelimbs and heavy tail.
This is a long list of objections (CARM user Wataru wrote replies to each of them at christiandiscussionforums.org). Some of these points are legitimate scientific riddles (i.e. embryological development and fingers), other points are irrelevant given a correct understanding of evolution (i.e. evolution is non-linear), and some seem like self-defeating admissions (i.e. the listing of other seeming dinosaur-bird transitions). But no explanations were given for the reptile-like features of some fossil birds like the Archaeopteryx. Any way you cut the deck, the Archaeopteryx and other such dinosaur-bird species are a fulfillment of evolutionary expectations, not of special creation.
Other creationists are more direct, and they say that Archaeopteryx was just another bird, a mosaic that God created, and there is no reason God can't create a bird with lots of things in common with a dinosaur. Yes, that's right. Maybe, on the Fifth Day, God created a bird with teeth, clawed wings, long bony tail, thick bones, and a spinal chord that connects at the back of the skull. And this bird presumably went extinct soon after its creation for being unable to compete with other birds that were more smartly suited for flight.
That is possible. But possibilities must yield to what is probable. The evidence from many sources lines up in favor of the theory that birds descended from theropod dinosaurs. That is consilience.
But wait there's more--we need other rungs on the ladder. This about the consilience of the evidence, after all.
Wikipedia has a long list of feathered dinosaurs. It can be hard to make out fossil feathers from a photo, but sometimes we are in luck. Here is a photo of a Sinornithosaurus.
Each of these species help to model a transition between theropod dinosaurs and birds. This is significant, because we haven't found any species that looks remotely like this:
Those animals are digitally edited, and if real they would be transitions between (1) birds and dogs or (2) birds and crocodiles, respectively.
For more, I found a slide show on the MSNBC website titled, 9 links in the dinosaur-to-bird transition. It talks about transitions in egg-laying behaviors, the T-Rex flesh, transition in size, transition in lungs, transition in feathers, and transition in feet.
Gentlemen, that is consilience.
Edited by Adminnemooseus, : Reduced size of some photos by making them thumnails.
This species was found just two years after Darwin published in book. It is a bird with teeth, clawed wings, long bony tail, thick bones, and a spinal chord that connects at the back of the skull instead of the bottom.
"Thick" isn't the right word, probably. Modern birds have bones that are hollow, to aid flight. Dinosaurs have non-hollow bones (thick bones). The Archaeopteryx has non-hollow bones.
This isn't entirely correct. First of all, one has to make a distinction between hollow bones, and pneumatic bones, in which air sacs involved in the pulmonary system invade the interior of the bone. Living birds have extensive pneumatization, and there's no consensus as to whether it's related to flight or not. Archaeopteryx had hollow long bones and limited pneumatization, and in non-avian theropods, which also had hollow long bones, pneumatization was limited to certain vertebrae and ribs.
Christiansen, P., & N. Bonde. 2000. Axial and appendicular pneumaticity in Archaeopteryx. Proceedings of the Royal Society of London, Series B 267:2501-2505.
O’Connor, P. M., & L. P. A. M. Claessens. 2005. Basic avian pulmonary design and flow-through ventilation in non-avian theropod dinosaurs. Nature 436:253-256. Available here.
Edited by Augray, : Edit stupid spelling mistakes.