Adapting Humans

New idea: suppose a population of humans became cut off from the rest of humanity in a harsh or extreme environment that pushed them to adapt. Talking micro evolution not macro but changes can still be dramatic like those between the wolf and dogs. They will still be human and capable of breeding with humans. So thought will need to be given to what the extreme or harsh environment is and how it pressures them to adapt. For instance on a water world humanity could develop webbing between toes and fingers.