On the Galapagos Islands, Darwin observed tortoises with domed and saddle-shaped shells. How did Darwin's observations of these tortoises help him form the theory of evolution by natural selection?

A.
The tortoises helped to confirm that environmental changes cannot affect the characteristics of a species.
B.
The tortoises helped to confirm that two similar species do not necessarily share a common ancestor.
C.
The tortoises provided evidence that different species have adaptations suited to their particular environments.
D.
The tortoises provided evidence that the Galapagos had been colonized by tortoises multiple independent times.

Darwin observed that how different environment on different island lead to the development of different species as a result of adaptations and natural selection.

For example, tortoise inhabiting well-watered islands which used to have short and cropped vegetation had developed a dome-shaped shell.

In contrast, the tortoise inhabiting the arid islands had developed saddle-shaped shells. It is because they needed to stretch their necks in order to reach branches of cactus and other vegetation available in the area.

Consequently, they developed long necks and high peak to the front edges of their shells. It made it possible for them to stretch their heads vertically.