Anyone who has run for years knows that over the course of years your form gradually improves. What if the reason that some kids start out so good at running and have such a "Natural, efficient stride" is not because of the genes that make their body in great proportion but the fact that some ancestor was a fantastic runner for years perfecting his/her form, that muscle memory is then passed on via their DNA to the kid, thus skipping years of learning to have good form. This would also accurately explain how and why running times will keep improving forever.
Give it a serious thought and post your comments below.