Most people do not really think to ask this question about Evolution. However, it has become quite the important question in determining the validity of the paradigm. In this post when I refer to "evolution" I am referring to macroevolution (see my post "Useful or Useless Evolutionary Terms"). If I am talking about microevolution, I will make the distinction.
As I discussed in the previously cited post, random mutation does happen, and natural selection does operate on those mutations. This observation has been extrapolated over time into the theory of Evolution. According to the paradigm, life began as a single-cell organism, and through the process noted, we arrive at the state of life today (complex, mega-multicellular organisms).
Most people familiar with biology know about the Long Term Evolution Experiment (LTEE). This experiment is touted as demonstrating that mutation does take place and can be observed. This demonstration is then used to conclude that Evolution is no longer a theory, and a proven fact (see the other post for the issues with this extrapolation- independent of the LTEE). Unfortunately, the LTEE actually raises a huge problem for the Evolutionary paradigm: the issue of historical contingency.
Noted evolutionary biologist Stephen Jay Gould describes Evolution as being unrepeatable. He used the analogy of a cassette tape. He stated that if the history of life was a tape, and that tape were rewound and played back, the second play would be radically different from the first.
Even though we can't rewind the tape of time and play it back, we do have multiple copies of the same tape. All we need is a highly controlled, stable environment, and we would be able to test Dr. Gould's theory.
The LTEE has demonstrated that random mutations that result in a usable feature will only repeat if the feature is only one mutation away from being produced. The frequency of that repeat was extremely small in the experiment. This means that random mutation can only produce the same outcome twice if the final mutation is a single step away, and the chances of that final mutation being the right mutation are minuscule (1 in 10,000). This supports Dr. Gould's theory.
So what's the big deal? We find many instances of "evolution repeating itself" in nature. One of my favorite examples is echolocation. Similar to SONAR. A high-pitched sound is emitted, and the sound waved bounces off objects back to the device. The location of the objects may be determined by the sequence of the sound waves received back. Both bats and dolphins possess this ability. Since they are so far removed from each other (from an evolutionary perspective), it is safe to say that the final mutation that led to the complete and functional echolocation system was more than a single step away. Which means that repeated echolocation is far from the possibilities of random mutations filtered by natural selection.
I've heard that some evolutionists will say that a similar environment would allow for such similar systems to evolve in different branches on the evolutionary tree. However, first that assumes that the same series of random mutations will take place for natural selection to favor. Based on the findings of the LTEE, that does not happen. Secondly, natural selection is driven by the environment. The two environments in which the organisms, that possess the same feature, live must be identical in the necessary and sufficient features at the time the feature "evolved". Thirdly, each mutational step needs to have function in order for natural selection to not weed it out. Multiple mutational steps are required for echolocation. Natural selection is not teleological ("forward looking" or purposeful), so it would not "know" to not remove a mutation that might be useful in the future, but not presently useful. Each mutational step will have to be accomplishing something that improves survival. Third-and-a-half-ly, when that mutation is no longer performing the function that improved survival, the survival advantage of that now-missing function must be accommodated. The new function must either improve survival sufficiently as to cancel out the now-missing function's improvement, or it may improve beyond the now-missing function. Or another simultaneous mutation (with equal or greater survival features) is required to supplant the commandeered mutation.
Dr. Gould is further supported. The first possibility above might be able to be demonstrated through further observations of the fossil record and study of earth's past climate at different geographical regions. The third, is conceivable via 3.5 (this is where Dr. Gould support ends- he still supported common ancestry), but that looks more and more like design with every qualification that must be made and with every slight change that must be accounted for. Even if the first and third could be explained naturalistically, the second poses the problem.
The problem is of nature contradicting what is demonstrated in the lab. If the theory states that evolution can repeat itself, then the LTEE provides powerful evidence that either that assertion is false or not enough time has transpired since life first began until now for life to reach the complexity that it has. If the theory states that evolution cannot repeat itself, then nature has proven it incorrect. Keep in mind that I am still referring to "evolution" here as "macroevolution". The LTEE does establish "microevolution", but falsifies a key component of "macroevolution". If the macroevolutionary paradigm is to survive this new discovery, it will need to be changed. The change would be that evolution can repeat itself, but only after more generations than the LTEE produced (but less than the smallest difference between two repeats that took place) or once a certain defined threshold is reached. Either way, as long as the LTEE continues, the new detail added to the evolutionary theory can be tested
For more details about the experiment's results and their implications, please read the article by biochemist Dr. Fazale Rana entitled "Inability to Repeat the Pass Dooms Evolution". Dr. Rana includes links in this article to other articles that he has written regarding the issue.
Now, the whole idea that I am demonstrating is not possible here, is common ancestry. There is much evidence that suggests a common ancestor (including similar genetic code). However, we are looking for an explanation that can make sense of the evidence for common ancestry AND all the evidence against common ancestry (surface scratched above).What is suggested by the similar genetic code is a "commonality". But what else could be "common" among the organisms that would explain all the evidence? A common designer. A common designer would explain everything. Many human designers use many things from previous designs in new designs (no sense in re-inventing the wheel). That would explain the common genetic code. A common designer is not limited by mutational and environmental pathways that are limited by the age of the universe and further limited by the age of whatever celestial body they formed on. The idea of a common designer explains more of the data, without inconsistency, than does common ancestry (macroevolution).
You may ask Dr. Rana questions by emailing email@example.com. I Didn't Know That is the podcast that answers will be given.
Two great podcasts that discuss convergence discoveries from time to time are Science News Flash and Intelligent Design: The Future.
Websites and Books
More about convergence is available from Reasons to Believe and Evolution News and Views.
Check out Wikipedia's list of 80+ examples of evolution repeating itself beyond a single mutation. This list does not include convergence at the biochemical level, which Dr. Rana shows in his book The Cell's Design.