Which one of the following phenomena supports Darwin's concept of natural selection in organic evolution?

The phenomenon that supports Darwin's concept of natural selection in organic evolution is the prevalence of pesticide-resistant insects. This is an example of how a population can adapt to a changing environment through the process of natural selection. In this case, the insects that are resistant to pesticides are more likely to survive and reproduce, passing on their resistance to their offspring. So, the correct answer is option C. Notice that the other options are not correct. The development of transgenic animals, the production of 'Dolly' the sheep by cloning, and the development of organs from 'stem cells' for organ transplantation are all examples of biotechnology, but they do not directly support Darwin's concept of natural selection.