The horse as an example of evolution:
For many years the evolution of the horse was used to support the idea of 'goal-oriented' evolution, where changes within a species occur one after the other in a straight line, so to speak, with the end result being the animals we see today. However we now know that evolution is not goal oriented, it happens sometimes at random, with similar traits evolving independently of each other and related species coexisting in overlapping timelines. As Kathleen Hunt states, "horse species were constantly branching off and evolving along various unrelated routes...[there are] several apparent trends....but these trends are not seen in all of the horse lines. We see a trend only because some lines have become extinct...Additionally, these traits do not evolve together, or at a steady rate. Rates of evolution depend on the ecological pressures facing a species".