Charles Darwin's Controversial Theory Of Evolution

In 1859, English Biologist Charles Darwin suggested a process in which species change over time which is known as natural selection. Darwin did not discover natural selection using genetics as he had no knowledge of genetics since it had not been discovered. Since then genetics has provided the solid evidence to support natural selection as the process by which evolution occurs. He began his journey in 1831 when he went to work on the HMS Beagle where he spent five years drawing maps of lands they visited and keeping a journal of their findings with his crew members. Darwin observed that many species that were related, faintly differed depending on where they were found. Darwin’s observation was influenced by the writings of Thomas Malthus, who proposed a constant battle for survival among species which led to Darwin’s Controversial theory The Origin of species in 1859. A century has passed since Darwin has presented his Theory of Evolution through natural selection where he argued that species

evolved to suit their environments. Darwin’s Theory argues that the inherited variation found among individual species will either hinder or help them. Those who inherited traits allow them to better cope with the environment and will be able favoured to survive and reproduce successfully. This favouritism will be a direct course of evolution over time, as species whose features make them better able to cope tend to increase over time. It is also learnt that characteristics is linked to another which is also known as genetic linkage. Furthermore, the fitness of a species is reduced when related individuals breed which is known as inbreeding.

Speciation is where two organisms of the same species breed to produce fertile offspring in natural conditions, and natural selection changes the features of this organism over a long period of time.

Over a long period of time organisms on an island change so they can no longer interbreed with organisms on different islands, the inability to interbreed in known as reproductive isolation. Reproductive isolation is due to Geographical isolation. A population can be geographically split in many ways which include Rivers form, Sea levels rise and fall, walls getting build, continents drift, climate isolation etc. If the environment conditions change for these populations they would then adapt to that environment, hence as long as they is no Gene flow between the two populations, they would genetically become different that they could no longer interbreed. An example of this includes a species of birds that once lived together, however now live on separate nearby

islands.
Close to the equator, in the Pacific Ocean on the Galapagos Islands there are a range or diverse finches which differ in the size and shape of their beaks. The finches colonised the mainland of South America and from then diverged in form. The long distanced between the islands meant that they could not interbreed, hence to populations on each island became distinct and created a variation in the population.
Consider the following diagram, it is noticeable that due to the absence of the other bird species, the finches adapted to their new environment. The finch’s beaks and bodies changed allowing them to eat certain types of foods such as fruits, nuts and insects. Different populations become specialised for diverse food sources, such as birds with thin, sharp beaks ate insects and birds with large, sturdy beaks ate nuts and seeds.

The most likely evolutionary pathway to form the four species of birds is B which illustrates birds from the mainland moving to islands one and three, and birds from island one moving to two and birds from island three moves to island four– slowly the size of the beaks differ due to the diverse environments. Over time these birds became so different that they were no longer able to breed and produce fertile offspring, which is known as reproductive isolation. Selection is the last step to speciation. Selection is where Natural Selection occurs to create changes in the genotype that prevent breeding between the populations in the future. Some changes include courtship behaviours, breeding seasons, sterility and chemical barriers. Between these finches their diets, behaviours, and bodies changed, therefore created change in the genotype and prevented breeding to occur. An example of an observation that would determine this include a flood that changes a course of a river dividing a population of deer. The deer can no longer interact or reproduce with the other population for many years, these two populations evolve and change dramatically to the point that their no long the same species. Eventually the river dries up and the two populations are able to mingle once again, however, they are no longer able to reproduce since they are no longer the same species.

Fossil skeletons of at least 17 different Genera have been found and dated, all these diverse types of horses form a family tree in which represents the development of new types of horses, however died out. Others evolved and eventually became another species. Regardless of the complexity of the family tree, palaeontologists were able trace a path which leads to the modern horse and have established a family tree line, and the species of its ancestors and the genus. One in particular includes the Mesohippus, a genus of a horse which lived around 40 million years ago. As time passed gradual changes occurred in many parts of the skeletons from all the different fossil horses. Some changes include that the body increases in size, the legs become longer, and the number of toes decreases, such as the Hyracotherium, which had four toes on its front legs, Mesohippus had three toe in which the middle toes seems to be thicker whilst the side toes are slightly smaller. A genus called Merychippus also had an enlarged middle toes and so did other species that appeared after this and eventually resulted to the Equs which is now the modern horses, donkeys, and zebras.
There are many thigs that modern scientists can do to confirm that these horse fossils have evolved from a common ancestor. During the last few decade scientists have been able to isolate genes to study their chemical structure and it has been discovered that the similar organisms are the more genes they share, hence as you move from the higher levels of classification to the lower levels, the similar the genes become. The characteristics in related species have the same basic structure which is known as homologous characteristics. A homologous structure does not essentially contain the same type of function in the groups that share it. An example includes humans, whales, and bats who all have five digits (fingers and toes) at the end of their limbs. The humans function is to grip and get traction when walking. Whale’s flippers are used to propel themselves through the water. A bat’s wings create the structure of their wings in which allow them to fly. A whale’s slippers, Human’s hand, and a bat’s wings are all homologous structures even though they have different functions. A modern horse runs on one large toe on each foot, which is comparable to the middle finger. Biologist believe the lost toes is due to adaptation which allows the horse to run faster while supporting the body.
Not all similar structures are homologous structures, such as a dolphin and a shark. They both have simular streamlined bodies and fins on their backs, however they are not humongous since they inherit different genes and differ in most of the structures, hence they are not very simular other than at the simplest phylum level in which the fossil records illustrates that sharks evolved over 460 million years ago, whereas dolphins evolved 10 million years ago. They have similar body lines and fins due to the similar marine environment in which they evolved in. Structures which look similar on generally different organisms are known as analogous structures. The cow and the modern horse is another example of an analogous structure, despite their feet structure looking similar they differ highly in other structural areas since different genes are involved in their inheritance.