Charles darwin was credited for writing the biological theory of the organisms that were used for the basis of his studies were

Charles Darwin was credited for writing the biological theory of Evolution by natural selection . The organisms that were used for the basis of his studies were Galapagos finches

Explanation:

It was in Galapagos Island that lie 1000 km west of Ecuador that Darwin made his most important observation. Here e carried out an intensive study on a group of birds called finches. He found several species of finches are adapted to different environmental niches. He found that each island was inhabited by its own kind of finch found nowhere else in the world. Some had beaks that were adapted fr eating large seeds, small seeds and others feeding on insects.