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I think the answer is Phenylketonuria.
Color change is the answer because that is a physical change
Investigating cricket will reveals that some specie of the insect produce a song by rubbing their legs or wings against each other. In those specie that sing only the male insect produce songs.
This observation can be taken to mean that the male song is a potential form of communication to potential mates.
Answer:
The beaver population increased
