Gumby,
You are applying the simplest mistake in definitions. Darwin was right in his basic premise. Note the title of his work “Origin of Species.” He discerned that speciation was the result of niche, isolation and competition. Key in here closely - darwinian evolution examines changes in a SPECIES over time. You Eohippus to modern horse is a nice example. Thank you for bringing it up. Note his book is not titled “Origin of Genus” or “Origin of Phylum.”
Yet evolution backers insist that those early horses could change species. That is my point, there is no evidence of one species changing to another. Adaptation is not evolution.