Analogous organs arise due to convergent evolution. Usually the cause of convergent evolution is similar selection pressures in the environment. In other words, the environments in which the two different species live are similar and those species need to fill the same niche in different areas around the world. Since natural selection works in the same way in these types of environments, the same types of adaptations are favorable and those individuals with those favorable adaptations survive long enough to pass down their genes to their offspring.