I am with Iain R on this Genes have Damn all to do with ability to run fast or slow. In fact there are far to many factors, such as distance, time of day, mental application, diet muscular/skeletal makeup, Lifestyle, both living and working environment terrain etc etc etc, so to even tryand begin to isolate a single one is futile IMO.
Back to topic well done Stolly looks like the key thing for you is the pleasure you get from running and TBH that is what running/walking infact doing any thing that float`s your boat is all about.