I'll choose Golden Retrievers:
These dogs where created for duck-hunters. Their purpose was to go catch the ducks that fell on the lake/river once they were shot by the hunter - here we see how they serve (or actually served) men.
Nowadays, Golden Retrievers are known to like water a lot, and to be very playful with it - and here is where we see a genetic adaptation. They needed to be in water, and were modified to like it.
Hope it helped,
BioTeacher101