The Evolution of the Horse
The evolution of the modern day Equus callabus species is said to have begun 65 million years ago, from the dog sized species called Hydracotherium, formally known as Eohippus. Mills Nankervis (1999)
Charles Darwin was the first to notice and record a process he called natural selection.
Alongside naturalist Alfred Wallace, Darwin noticed and documented…
Variation: Differences with a species
Hereditary: Parents passing on traits to off spring
Competition: Survival within a species.
Adaption: The ability to adapt to environmental, predatory, external factors
Natural selection: Surviving, not just due to being the fittest, but maybe the smartest, quickest or tallest etc. Whye J.V (2002) the complete works of Darwin on line <http://darwin-online.org.uk
The evolution of the horse it is said to be one of the most complete examples of evolution.
Beginning after the extinction of the dinosaurs and the rise of the mammals at the dawn of the Cenozoic era. Podhajsky A.W Gus Cothran E. (01-05-2017) Britannica Enclopaepia inc <https://www.britannica.com/animal/horse/Evolution-of-the-horse>
The equidae adapted to regional differences effected by the world climate and continent changes, creating varied groups. These groups adapted to differing environmental factors which changed their phenotypes. Gradually the genotype would reflect this through the mutation of DNA.
Mutations are responsible for evolutionary changes to a species over time, resulting in a change physically and/or behaviourally to a species individual.
That individual then carries hereditary DNA, alleles which are passed on through reproduction.
Genetic Flow adds variation to the Equidae groups. At varying intervals a link was formed between North America and the old world called the Bering Strait. Mills Nankervis (1999). This enabled stallions and/or groups of horses to migrating and reproduce with each other, mixing their DNA and producing a varied population. Sometime by chance and not always due to natural selection more of one population may survive than another. This is known as genetic drift.
‘Evolution 101’ Understanding Evolution. University of California Museum of Paleontology. 22 August 2008 <http://evolution.berkeley.edu/evolibrary/article/evo_24
Climate change would force the equidae to adapt from a browser to a grazer and the development of high crested crowned teeth (hypodonty), in a longer deeper jaw. It is thought that Macroevolution may have played a part in the hypodonty development, particularly the Miocene grazers. MacFadden (2003) Stirton (1947)
Via Natural selection populations with speed, size and awareness would survive their new environment grazing out in the open. Lateralisation of the eyes and a more advance neocortex also became evident. Genetic flow would enable the variation of genes with the new mutations to spread.
Microevolution would result in the merging and fusing the 2nd, 4th and 5th toes, to the main 3rd toe creating a single hooved and longer limb
Further microevolution would see mutations effecting the digestive system creating a hind gut fermentation system better equipped to deal with grass. Regional mutations and gene flow gave rise to variations within the species such as smaller bodies, hooves and a finer coat on equidae found in warmer dryer regions. With larger bodies (Bergman’s rule), hooves and a thicker coat being found in coolers regions.
In recent times humans have effect the natural selection and genetic flow of the equidae by domestication and breeding programs.