I am always amazed by the willingness of my very intelligent quarter horse to work with me, and puzzle out that thing that will earn him praise.
It is said that the first horse was ridden in 4500 BC.
I think this confirms what I've always felt. Somewhere along the way it has become MORE natural to ride horses, predatory humans with eyes in front of their heads or not.
I would also point out that horses are naturally social creatures, and many indisputably enjoy socializing with members of the human species..
So define natural.
I definitely feel a spiritual connection with my horse when riding or playing. And who can't say the same with their babies?
Maybe it isn't "natural" for predatory humans to love and cherish flighty 4-legged vegetarians... but they do.
And it certainly feels natural to me!
As an endnote, I am also dissappointed by the insane marketing explosion with all the natural stuff. Just human nature to want to make lots of money, I suppose. And it sure works, huh?
I personally would say just plain ol' riding is as natural as it gets!