Thorns (IMAGE) University of the Witwatersrand Caption Trees in Africa evolved thorns as a defense mechanism as a defense mechanism against medium and large antelope on the continent. Credit Gareth Hempson Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.