Human body:
After becoming a mammal, evolve the cat jaws and rabbit body.
Then, select the Ramopithecus body. It will become human after
two more evolutions.
Mermaid body:
Accumulate 10,000 evolution points by the final ocean stage of
Chapter 5. Select "Hand and Feet" when evolving your character,
then select the "Try To Evolve option". Continue to evolve three
times to become a Mermaid.
Sites: