Eohippus is related to the modern-day horse through a process of evolution over millions of years. Over time, Eohippus and its descendants gradually changed and adapted to different environments. The number of toes on each foot decreased from four to one, the neck became longer, and the skull became more elongated. These changes allowed the horse to become faster and better adapted to running on open plains.
The evolution of the horse from Eohippus is a classic example of macroevolution, which refers to large-scale evolutionary changes that occur over long periods of time. It demonstrates how species can change dramatically through natural selection, adapting to new environments and surviving in the face of changing conditions.