As was stated before, no one but you said that there's no evidence.
There is: living beings do reproduce, and their descents are not clones of themselves, that led us to "descent with modification", unavoidable.
So, if we do not invent anything to explain the existance of actual or past's lifeforms, and knowing that there was old lifeforms, the logic suposition is that the nowadays ones are descendats of the old ones. Genetics says to us things about inheritance and the expected patterns of modification by descendance. Horses, as any other living being known, fits the expectancies. There are the fossil pattern, and the genetic pattern itself, with things like atavisms, and vestigial developments, that may disapear laterly.