Here's why:

* Homologous structures: These are structures in different species that share a common ancestral origin, even if they have different functions.

* Human arm vs. whale forelimb: While a whale's flipper looks and functions very differently than a human arm, they both share the same underlying skeletal structure:

* Humerus: Upper arm bone

* Radius and Ulna: Forearm bones

* Carpals, Metacarpals, and Phalanges: Hand bones

This shared skeletal structure is evidence of their common ancestry, suggesting that both humans and whales evolved from a common ancestor that had a similar forelimb structure. Over time, these structures have been modified and adapted to suit their specific environments and needs.