Another good reasoning for the theory of evolution is that there is evidence in every species, not just a select few. There has been proven genomic changes over time, which helps assume the influence of a shared common ancestor. As fossils are found and dated, scientists have also noticed continuous change in their characteristics and the fossil record in general.
Most notably, however, is the constant adaptation of bacteria in their ability to resist antibiotics. This works as its own form of malicious natural selection. When a new antibiotic is developed and dispersed, the bacteria that are unaffected (usually due to a random mutation) will reproduce and pass along that mutation (as the genetic code is identical), and soon the antibiotic will be rendered useless in killing off the harmful bacteria.
Evolution is constant in this never-ending cycle, along with that of pesticides, herbicides, and even chemotherapy drugs. Even worse, pathogens will continue to evolve and cause emergent diseases that were once eradicated.