How did tortoises varied from island to island?

Tortoises varied from island to island primarily due to differences in environmental conditions, such as food availability and climate. These variations led to distinct adaptations, such as differences in shell shape and size; for instance, some islands had tortoises with dome-shaped shells suited for dense vegetation, while others featured saddle-backed shells that allowed for easier grazing on higher vegetation. These adaptations are examples of natural selection acting on isolated populations, contributing to the diversity of species observed in the Galápagos Islands.