Why is the fossil history of the horse so important for explaining the evolution of complex lifeforms in recent history?
The fossil history of the horse is one of the most complete records of change in a large mammal
Many textbooks use the example of the fossil history of the horse to illustrate evolution or change in a complex organism. In 1882 Othniel Marsh published a series of drawing showing how the modern one toed horse had evolved from a small four toed ancestor.
The Hyracotherium had four toes in front and three toes in back. The Mesohippus a supposed answer of the early Hyracotherium had only three toes in front and three toes in back. This is a change in the number of toes and adapted the horse ancestor to be able to run faster.
Another horse fossil the Protohippus had three toes in front and three toes in back but only one of the toes actually touched the ground in running. The other two toes were regarded as vestigial structures.
The modern horse has only one toe which makes it much better adapted for running.
The fossil horse record is used as indirect evidence of Darwinian evolution or change based on adaptation . The fossil horse record is also used a direct evidence against the Neo Darwinian theory of evolution.
The Neo Darwinian theory postulates that mutations (accidental changes in the DNA ) can account for the increase in complexity of life forms. The horse fossil record while it illustrates change it shows a marked decrease in complexity of the organism. Moving from a total of 14 toes down to a total of 4 toes is a decrease in complexity.
The fossil history of the horse is important because it is one of the earliest "proofs" of Darwinian evolution. It is also used as one of the arguments against Neo Darwinian evolution, making the fossil history of the horse important to both sides of the argument.