I havn't noticed too many mammals that are heel strikers. As can be seen with dogs, most of them only use their heels when they are sitting/resting. I believe the same should be true for us, only to be used while standing still. Watching people walk would seem to prove we are natural heel strikers, until you take into account we are not naturally shoe wearers. If you would like to know which way is best for you naturally speaking, take your shoes off and start hauling ass...pretty sure you'll find heel striking is horrible.