Explore Evolution begins its discussion of natural selection with a discussion of artificial selection. Artificial selection, in which differential survival and reproduction in animals, plants, or other organisms is driven by the choices of human breeders selecting among natural variations in a population, is treated as an analogy for natural selection, in which differential survival and reproduction of organisms is driven by natural processes acting on natural variation in a population.
This is a dubious beginning, as natural and artificial selection are, in fact, different aspects of the same process. While Darwin's early understanding of natural selection was influenced by his ability to draw analogies between natural observations he made and the actions of humans breeding pigeons and dogs for special traits, it is wrong to suggest that our modern understanding of these processes is merely analogical, rather than treating artificial selection as a special application of the principles behind natural selection.
Explore Evolution further errs in presenting results from a few hundred years of intensive breeding in dogs and horses as evidence for limits in evolutionary processes over thousands, millions, and indeed billions of years. Even if horses and dogs demonstrated the limits claimed by the authors, it would be foolish to extrapolate limits found under the special conditions of horse-breeding and dog-breeding to the longer-term and more complex conditions which natural selection must confront in its more general form. Given the track record of Explore Evolution, it is hardly surprising that artificial selection in dogs and in horses has not actually reached clear limits, and what limits can be inferred from those cases shows that the variation which can be produced in even a thousand years or so is greater than that seen in all of the members of the mammalian family Carnivora other than dogs. If such extrapolation is legitimate, the actual evidence undermines the point Explore Evolution seeks to make with those data.