Phil,
Very logical, which is why I believe the assumption on horses was incorrectly made.Not sure where Bailey was but I stood 5 feet from Dr.Fager, Secretariat and many others from 40+ years ago.The horses of today,generally speaking,are NOT bigger(as in 16+hands) and certainly not 12 lengths faster at the top level.Many modern horses, pre steroid ban were very barrel chested and massive,don\'t see that any longer.Not certain Bailey just not repeating what DR.Arthur said recently.
Check out Andy Beyers figs of the horses of which I speak,they are just as fast as many of the modern day horses.The very large animals of 50 years ago stood 16+ hands,just like today.The greatest diffence between yesterday and today race horses is definitely in the claiming ranks where todays runners are faster.
Humans a way other story,I knew 10 guys that were six feet tall 50 years ago, now I know many.
Example, NFL Hall Of Fame defensive lineman from 40 years ago would not be big enough or fast enough to make an NFL roster today, on the other hand, horses like Dr.Fager/Secretariat and others would be very competitive today.
Mike
Edit for Rick B,
Gravitated over from harness racing long ago.Harness horses 30+ lengths faster from back when but really not much larger in size if at all.