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Evolutionary Development of the Horse
The horse is a hoofed mammal, a subspecies of the family Equidae, that has evolved over the past 45 to 55 million years from a small multi-toed creature into the large single-toed animal that we know today. The fossil record of the horse is extremely complex and detailed, probably due to the fact that paleozoologists have managed to put together the most complete picture of the horse's evolutionary history than that of any other animal. Another likely difficulty stems from the non-linear structure of the horse's evolutionary process. There are many branches of horse evolution, which makes daunting the prospect of conceiving an evolutionary diagram that accurately relates all the horse's evolutionary mechanisms. (Simpson, 1961) The horse as a vertebrae group is fairly well-known, and the modern view of evolution within this group is somewhat difficult to simplify and summarize. The majority of horse species arose in North America, including all the ancestors of the Equus. A sequence of their transitional fossils was first discovered in the 1870's by the paleontologist O.C. Marsh. This astonishing new find was a clear and precise depiction of evolution taking place in a single lineage. The fossil species Eohippus (the term was later changed to Hyracotherium) transformed into the recognizable form of its descendant, Equus, through a series of very clear intermediaries. This is what led the horse family to become the evolutionary standard used in museums,…
The biological classification of the domestic horse, which is the animal that most people picture when the term 'horse' is used, is as follows: the horse belongs to the Animalia kingdom, the Chordata phylum, the Mammalia class, the Theria subclass, the Eutheria infraclass, the Perissodactyla order, the Equidae family, the Equus genus, the Equus Ferus species, and the Equus ferus caballus sub-species. The evolutionary process of the horse occurs within the categories of the family and the genus. (Hall and Olsen, 2007)
The small horses of the Eocene period, about 20 million years ago, were doggish in appearance with arched backs, short necks, short snouts, short legs, and long tails. The first Equid was Hyracotherium, a small forest animal of the early Eocene. In the early-middle Eocene period, Hyracotherium gradually gave way to the Orohippus, who closely resembled his ancestor with minor changes in the toes and significant changes in the teeth. During the middle Eocene the Epihippis arose from the Orohippus. This animal was also very similar to his most previous ancestor, with a great deal of tooth evolution taking place in this transition. There is a late form of Orohippus called Duchesnehippus, with teeth similar to later Oligocene horses, and it is unclear whether this particular creature is a subgenus or a species of Epihippus. (Simpson, 1961)
Prothero and Shubin (1989) tell readers that the late Eocene period and the early Oligocene period brought about a great deal of change in the horse, due to climate and foliage changes. North America was becoming drier, grasses were beginning to evolve, and forests were shrinking. Horses of this time period developed tougher teeth and longer, stronger legs for running. The species Mesohippus celar
" (Wikopedia, n.d.) The social scientists moved from Freud to the idea of Pramatism. "Theodore Porter argued in "The Rise of Statistical Thinking" that the effort to provide a synthetic social science is a matter of both administration and discovery combined, and that the rise of social science was, therefore, marked by both pragmatic needs as much as by theoretical purity." (Wikopedia n.d.) An example of how the social science movement continues
Since males of all sexually reproducing species are naturally drawn to signs of fertility in females (Zuk 2002), they naturally express more interest in females when they ovulate, or come into heat in the vernacular applied to non-human animals. In many other species that do not rely as much on a monogamous pair bond for the survival of the fetus (Barash & Lipton 2001), females exhibit very clear external signals
They accuse Coyne of giving modern intellectuals "permission to remain biologically illiterate, through assuring them there is nothing useful or important that they could learn that would help them address the intellectual problems they face." (Tooby and Cosmides). Without undertaking an independent investigation of the evidence used to support each author's work, it is impossible to determine who makes the most valid arguments. However, if the facts listed argued by
In males, the canine teeth tend to be longer, and sharper. Additionally, there appears to be greater variation in size and shape of male canines, in comparison to the relatively stable size and shape of the female canine. Often, the size differences between male and female teeth are seen more in the height of the crown of the tooth than in the length or width of the lower portions
Evolution and Development of Dog Species: According to the findings of previous research, it has been suggested that dogs are paedomorphic wolves that have evolved through heterochrony. Heterochrony is described as an evolutionary technique that produced diversity through perturbations of the timing and rate of development, which needs very minimal genetic innovation. Consequently, this evolutionary technique is considered to be the most common mechanism in the generation or production diversity (Drake,
EVOLUTION What is evolutionary theory and what are causes of evolution and the evidence of evolution? The term 'evolution' evokes varied connotations. In simple and direct terms it is a process of change or development over a long period of time. Defined so, evolution can refer to any phenomena-- evolution of universe, evolution of human culture etc. -- that change over a period of time. However, in common parlance, evolution refers to