Just for the record.

Animals evolve into their bodies and body parts become 'specialty' traits.

Dogs?

Whippets and GHs got the legs to run, terriers got the speed and the digging gene?

Sledders? St Bernards? Coats to keep them warm. Looking at a horse you would have to guess that long lean legs would be a predisposition to speed.

When you look at the long-legged animals, deer, giraffes and elk- they all have the speedy leg look. It only makes sense to assume that a horse is a runner.