Evolution by Mutation

One of the tenets in the theory of evolution is that organisms evolved by mutation. The theory is that something caused a mutation in the genetic material of an organism. This change in the genetic material resulted in a change in the physical characteristics of the organism. If the change was a positive one, then the new organism would be more complex than the original and would have a survival advantage and therefore would be more likely to thrive and propogate. This would result in new family of more highly evolved organism that would continue to multiply until one of them would have another positive mutation and repeat the process. Thus, over a long period of time, life would move towards more highly evolved organisms.
I have seen a lot of evidence for mutations. They can be either harmful, neutral or beneficial. The majority of them are harmful, some are neutral, and a few are beneficial. Mutations can be caused by chemicals, radiation, or sometimes there is a mistake in the replication of the DNA molecule. The problem that I have with the concept of mutations resulting in a more complex organism is that I have never come across such a case. There have been mutations that have changed the characteristics of an organism so that it is better equipped to survive in its environment (beneficial mutations) but this is not evolution, it is adaptation. In an adaptively beneficial mutation, part of the genetic code has been deleted or suppressed or changed to create new characteristics that by chance give the new organism an advantage over the old. There would be a tendency for the new organism to survive longer and thus have a higher probability of propagating its genetic code but again, it is not more highly evolved. It is simply a remixing of the original genetic code. I have never heard of a mutation that resulted in a more complex genetic code. An organism that becomes resistant to an antibiotic, more camouflaged in its surroundings, or has developed a stronger beak for breaking food has not evolved. It has adapted. A different characteristic has become more prominent. There is no increase in complexity. This does not seem like a reasonable way for evolution to occur.