Why do whale flippers have finger bones?

Answer 1

Because whale ancestors were land animals with distinct digits. Over millions of years, their limbs evolved into flippers as they spent more time in the water. Those with flipper limbs that allowed them to get around with greater ease survived to pass on their genetic traits through aeons of evolution. And now we have whales.

(The nature of whale predecessors is also why whales breath air instead of taking in oxygen through gills, like fish - they're still stuck with remnants of land-dweller Biology.)

Answer 2

They need to maneuver themselves through the water (and not drown). They have the longest flippers of any whale (1/3 of it's body length) because they need to be very maneuverable to catch their prey.

Answer 3

Obvously, to swim.