There were many things that Charles Darwin didn't know about evolution. They were discovered by scientists in the centuries to come. Three kinds of evidence for evolution that were discovered after Darwin's times are:
- speciation in action
- key transitional species
- molecular biology evidence
An example of speciation in action is so-called ring species.
When territories of two different, but related species of animals partially overlap, they can often interbreed. So you have a chain of several species, and any two neighboring species can interbreed between themselves. In a way it's like a spectrum: on one end there is "red" species, which then morphs into orange, yellow, green, and blue. Any color (or at least, individuals on the ends of any color) can interbreed with neighboring colors. But if the "blue" species migrates into the territory of the "red" species, they often find they can't interbreed anymore. Too many genetic differences have accumulated. Yet since interbreeding is possible all the way from red to blue, we don't know whether to consider them separate species or one big species. All that it takes for this group to separate into different species, is for some intermediate species to go extinct. This has happened in nature. Ring species illustrates how concept of species is arbitrary "in a cosmic context" (to quote Dr. Moore), but is meaningful in human context.
Many people imagine transitional species to be something akin to a mythical crocoduck kirkcameronii (here Moore showed a picture with a head of a crocodile and body of a duck). This, of course, is not what transitional species are like. A real example would be Achaeopteryx lithographica, a primitive bird with a lizard tail. It has wings and feathers.
How do you get from a fish to a tetrapod? Most people think there must have been something fishy-like that grew legs. But we haven't found a good example of it until discovery of Tiktaalik roseae in 2006. This shows predictive power of evolution. Scientists were able to predict in what type of rock, what type of location they could find something like this -- a fish-like creature with appendages resembling legs. It has a tail with fins, it also has gills. But the front fins were very different: they had primitive wristbones. It could push itself up with them. It also had a very unfish-like head, and a neck.
Another remarkable transitional species is Ambulocetus natans, a walking whale, discovered in 1996. It's a mammal that's perfectly adapted for aquatic life.
While the subtle points of the argument might have escaped me, the gist is that similar molecular sequences in ubiquitous genes indicate a genealogical relationship between species.
Pictures from Darwin Day can be found in my photo gallery. I will keep adding new pictures in the days to come.
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