Or can you only play this +1 action to another tribe member's related base ability? THis seems the most logic to me....
Feedback is appreciated...
Your instincts are correct about the second interpretation being the correct one.The Mentor's ability will allow a refugee to add +1 to another tribe member's action, as long as that tribe member already possesses the base ability to perform that action.
Hope this helps! Enjoy this wonderful game!