Darwin famously used human breeding of crops and animals to demonstrate natural selection by analogy. After all, the whims of the human selection process become part of the environmental pressures acting on the genes of the organisms being bred. As Darwinism suggests, the plasticity of selection is great, as these tiny horses show.
In recent years, the genetic underpinnings of height and size in mammals have generated increasing interest from scientists. In 2007, genetics researchers made the surprising finding that a single gene plays a very large role in regulating dog size, a fact that partially accounts for the tremendous variation in dog size that we see from tiny chihuahuas to enormous bull mastiffs.
Brooks is attempting to do similar genomic studies of horses, drawing on a new genetic data set she’s created from the DNA of 1,300 horses ranging in size from 29-inch tall mini horses to draft horses that are more than 6.5 feet tall at the shoulder.