Many museums and school textbooks today depict horse evolution as orthogenetic. That is, variations in the fossil record of the horse follow a particular direction and are not merely sporadic. In other words, evolution is supposed to proceed undeviatingly in a single direction, regardless of environment, organic activity, or such factors as natural selection. This is **not** what evolutionists teach today. Orthogenesis has been proved wrong and is no longer accepted by evolutionary scientists.
Notice this comment by the late Dr. George Gaylord Simpson, world renowned evolutionist and palenthologist:
“Orthogenetic evolution is supposed to proceed undeviatingly in a single direction, regardless of environment, organic activity, or such factors as natural selection. Discussion of this point has been so lengthy and extensive that it has, frankly, become boring. There is at present a clear consensus of paleontologists that orthogenesis, in this sense, is not real. There is no known sequence in the fossil record that requires or substantiates such a process. Many examples commonly cited, such as the evolution of the horse family or of sabertooth “tigers,” can be readily shown to have been unintentionally falsified and not to be really orthogenetic. All supposed examples are more simply and fully interpreted as due to some other cause, such as natural selection.” (emphasis mine).
Both creationists and leading supporters of the Theory of Evolution believe that evolutionists teach that the modern horse, Equus, has evolved from the forest dwelling Eohippus, which was no bigger than a dog. In fact many modern museums still portray the evolution of the horse leading from the Eochippus to Equus the modern horse. Yet, this is in error and is not supported by Natural Selection, the vehicle of evolutionary science. Notice:
“We conducted a systematic survey of 20 fossil horse exhibits from natural history museums in the United States. Our resulting data indicate that more than half (55%) of natural history museums today still depict horse evolution as orthogenetic, despite the fact that paleontologists have known for a century that the actual evolutionary pattern of the Family Equidae is branching.”
In other words, the so-called chart of the evolution of the horse is better explained by micro-evolution, or the species adapting to its environment through the process of natural selection. Just as there are many breeds of dogs in varying appearance and size, so the horse has many breeds, in varying appearance and size. The horse, zebra and donkey may even have a common ancestor, but this is not evidence for the Theory of Evolution, but evidence of environmental adaptation and natural selection. Micro-evolution (breeding – natural or controlled) is a fact of science, but it is not evidence for macro-evolution, or lifeforms evolving from one species into another such as evolution postulates concerning birds and reptiles.
 George Gaylord Simpson, “Evolutionary Determinism and the Fossil Record”, Scientific Monthly, Vol. 71, Oct. 1950, pg 264.
 See Horse Evolution Over 55 Million Years; http://chem.tufts.edu/science/evolution/horseevolution.htm ;
 Fossil Horses, Orthogenesis, and Communicating Evolution in Museums; http://link.springer.com/content/pdf/10.1007%2Fs12052-012-0394-1.pdf