Try this guide:
1. Control + mouse click The Fertile Crescent 0.5.4 execute and pick Show Package Contents.
2. Open Contents and control + mouse click MacOS folder and pick New Terminal at Folder (bottom of list).
3. Type "chmod +x The\ Fertile\ Crescent (if executable is on desktop, or else you need the full path)
4. Close terminal and Control + mouse click executable icon again, and pick Open.
5. When asked about being an unidentified developer, click Open.
6. From now on you can double-click the executable icon whenever you want to play.