There has been a number of threads related to evolution in the last month or so. Some posters, like Penn, subscribes to a form of creationism, which I for this purpose will define as denial of large scale evolution (sometimes called macro-evolution).
Even saner people sometimes alleges that scientists are unnecessarily 'dogmatic' about evolution, and that this is 'just a theory.' These people may be recent exJWs or JWs, still believing the Watchtower propaganda against evolutionary science, or accepting similar claims from various fundamentalist preachers and groups. Often, creationists attribute scienists' acceptance of evolution to some materialist or even atheist prejudices, and deny that the evidence itself is totally in favor of evolution.
However, scientists are certain about evolution on the merits of facts alone. The body of evidence for evolution and against direct creation was overwhelming already in Darwin's days, which was the reason his controversial views eventually were accepted by the majority of scientists and other intellectuals (including many Christians). Today, the evidence is stronger to an extreme degree. Especially after the discovery and development of genetics, the fact of evolution simply cannot be denied by any rational person who is aware of the facts. Hard words, but they can be backed up by hard facts.
I will simply outline one line of evidence, actually in itself sufficient to establish large-scale evolution as a fact. Take note that much more evidence is available.
DNA evidence has a tremendous prestige in courts of law, for a good reason. And for similar reasons that a court can e.g. conclude pretty conclusively kinship between a father and a child, science can conclude we are very closely related to e.g. chimpanzees, and related more distantly to all other species on this planet.
It is a well-published fact that we share about 99.7 % of our DNA with the chimps. The most interesting fact in this context, however, is related to what is called psuedocode or junk code.
The question of common descent between humans and other species on this planet is no longer up for debate. And it's the DNA that gave us the ultimate smoking gun.
You may be aware that some map makers put "copyright traps" into their maps. That is small irregularities not important for the map's purpose. If someone copies the map and tries to sell it as their own, including these intentional "errors", any court of law will convict them of copyright violation. It will be beyond reasonable doubt that they copied from the map, not the terrain. In the same way some students have been caught cheating by presenting works downloaded from the Internet as their own, and just changing a few sentences. If they are caught duplicating grammatical and spelling errors from the original, it is almost impossible to make anyone believe their are coincidental.
As it is, our DNA is full of errors. While it is true that the replication of DNA is remarkably accurate, errors do occur. Every human being has a number of mutations in their code. Most such errors have no consequences for the phenotype (= us).
However, as times goes by and evolution changes species considerably, this means a lot of junk accumulates in the DNA. In fact, most of the DNA we have in us -- and this is true about every other organism -- is useless junk code, so-called pseudocode. Some of it contains copies of code used elsewhere (reduplications). Lots of it is code that was used by some of our ancestors. And, when we see that we share these meaningless sequences with chimps and other species as well, it is direct evidence to the fact of evolution.
Bits and pieces of this pseudocode made sense once, when it was carried in our distant ancestors. Some of it was perhaps used to make gills on a fish, to control the temperature in one of our reptile ancestors, or, more recently, they provided the tails that some of our ape-like ancestors had. And in the latter case, we can see direct evidence quite often: it is not uncommon that a human baby is born with a visible tail (promptly removed with modern surgery), a throwback to our ancestors and direct evidence that we descend from a species that had tails. If this is not direct evidence for macroevolution, what is?
Other species have more dramatic throwbacks. Sometimes, a whale is caught which has the bone structure of hind legs inside its fish-like body structure. Whales with legs? Yes, throwbacks to the time when the ancestors of whales walked on dry land. This is absolute, undeniable evidence that the whales descends from land animals, just as the theory of evolution predicted. If this is not direct evidence (or proof, as many would say) of macro evolution, what could possibly be?
In the same way, we know that modern birds have genes for teeth, even though no modern bird has teeth. By transplanting tissue from the jaw area of bird embryos elsewhere, experiments have been able to see birds develop teeth in our days! Why should birds have genetic "blueprints" for teeth in their DNA if it was not true that ancestors of birds did indeed have teeth?
No creationist should be allowed to repeat their silly assertions without being called to task to reply to this question: If we and other species were created directly, how come we have genes for tails, birds have genes for teeth and whales have genes for legs, genes that are sometimes actived today? In the creationist world, such a thing would be impossible. In the real world, one where all species is the result of evolution -- descent with modification -- such throwbacks are both possible and exactly what we should expect.
This is just one reason we know that evolution is a fact.
- Jan
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"Doctor how can you diagnose someone with Obsessive Compulsive Disorder and then act like I had some choice about barging in here right now?" -- As Good As It Gets