What led Darwin to believe that organisms originate from a common ancestor?

The belief that organisms originate from a common ancestor was much of the basis that the theory of natural selection was based on. Evidence of animals sharing the same trait, even though for some it appears to have no benefit to them, appears to have been at the root of this belief.

Charles Darwin was the first scientist to publish a coherent theory of Evolution by Natural selection. He wasn't the first to intuitively suspect that species evolved from a common ancestor, but he was the first to publish a coherent theory and bring forth evidence for it.

The belief that organisms originate from a common ancestor was much of the basis that the theory of natural selection was based on. Evidence of animals sharing the same characteristic, even though it appears to be of no advantage to some, appears to have been at the root of this faith. Charles Darwin was the first scientist to publish a consistent theory of natural evolution.