While there is only one species of Galapagos Island tortoise, there are several subspecies. Larger islands with more wet highlands have lush vegetation near the ground. Tortoises there tend to have high-domed shells and shorter necks, which restrict upward head movement. They also have shorter limbs. They are the heaviest and largest of the subspecies. Smaller drier islands are inhabited by tortoises with longer necks and limbs and with shells that are elevated above the neck, which allow them to browse taller vegetation. Based on the information given, which is a plausible explanation for the ancestry of the tortoise subspecies?

Tortoises with better adaptations in shell shape and leg length were selected to exploit the food resources on each island and, thus, they were capable of having more offspring.

Explanation:

Natural selection can be defined as the process of differential survival and reproduction in a given environment due to differences in their phenotypic traits. Thus, these phenotypic traits are selected to be better adapted to their environment. As a consequence of natural selection, organisms evolve by changing their phenotype frequencies over many generations. In this case, phenotypic differences are expressed as variations in shell shape and leg length, which are adaptive traits that were selected on each island.