Tag: #darwinism

Theories of Evolution – Darwinism

Charles Robert Darwin (1809-1882) was a British biologist, born on 12th February 1809 in Shrewberg, England. 

He presented his theory of evolution in the book On the Origin of Species by means of natural selection in 1859. Darwin argued that new species had evolved from older species, and he described the mechanism behind the transformation process. Darwin’s theory of evolution is based on the following five principles: 

  1. Organisms produce more offspring than can possibly survive.
  2. Organisms face a constant struggle to survive.
  3. Organisms within a species vary.
  4. Organisms best suited to their environment survive.
  5. Those organisms which survive will reproduce and pass on their genes to the next generation.

  • Over-production: All species have a tendency to produce more and more offspring in order to increase the population. For example, a salmon produces 28,000,000 eggs in a single season; a single spawning of an Oyster may yield as many as 114,000,000 eggs; a common roundworm lays about 70,000,000 eggs in a day. This huge production is to ensure the survival of the species. Even though species are produced in larger numbers, the population of a particular organism remains more or less constant.

  • Struggle for Existence: Darwin claimed that there was a continual ‘struggle for existence in nature, in which only the fittest would survive. As a result of overproduction, there is a struggle for existence among organisms. Since the number of is persons is large, there is competition for food, shelter, mates etc.

 struggle for existence may be of different types as follows: 

a. Intra-specific (Intra-species) struggle: The members of the same species struggle among themselves for food, shelter and mates. 

b. Inter-specific (Inter-species) struggle: The members of different species may go on fighting for survival. A member from one species may hunt other members of other species for food. 

c. Environmental struggle: Organisms of different species struggle against the environmental hazards like earthquake, flood, drought etc. Only those species with better adjustment with the environment will survive.

  • Variations: Variation is the tendency of an organism to deviate from the parental generation. These variations play a very important role for adaptations in the environment. Some variations are considered as favourable and others are unfavourable. Organisms with unfavourable variations easily get defeated in the struggle for survival. Variations that are useful to adapt to the pressures of the environment survive long. The new trait of advantageous characteristics is passed on to the future generations. 
  • Survival of the Fittest: The struggle for existence leads to the survival of the fittest. When there are too many of an organism in an area, they compete for resources such as food and perhaps shelter, for example trees and caves.The surviving species will reproduce more offspring than those who are less adaptive.
  • Natural Selection: The surviving individuals will give rise to the next generation. The successful variations are transmitted to the succeeding generations. The accumulation of advantageous traits in future generations gradually brings changes in species. Successive generations in this way tend to become better adapted to their environment. Eventually, a new species may evolve. 

Furthermore, certain members of a population with one group of variations may become adapted to the environment in one way, while others, with a different set of variations, become adapted in a different way or become adapted to different environments. In this way, two or more species may arise from a single ancestral stock. 

Examples of Natural Selection 

1. The finches of Galapagos : Some species of finches have short thick beaks. They are used to eating seeds, fruits and buds. Some others have long straight beaks. They subsist primarily on nectar from flowers. If environmental condition suddenly changes some characteristics may be more favoured than others. 

2. Industrial melanism in moth : Before Industrialisation, the tree trunks were lighter and light coloured moths were predominant. Dark coloured moths were also present but they were limited in number. As a result of industrialisation, the pollution resulted in the darkening of tree trunks. So the light coloured moths become more visible to birds and were therefore eaten by their predators. As a result of this at the end of 19th century the common light coloured moths were almost completely replaced by the black variety.

The theory of origin of species by natural selection is regarded as a major advancement in evolutionary thought. Darwin contributed to the modern understanding of biological evolution by documenting the variation of living forms and identifying the key process of natural selection.

 Like most 19th century scientists, however, he did not understand heredity or how specific traits are passed from one generation to the next. His theory lacked the knowledge of modern genetics. However, mutation theory explained the causes of variations among organisms.

DARWINISM AND THE THEORY OF ORGANIC EVOLUTION

WHO WAS DARWIN?

Charles Robert Darwin was an English Naturalist, born on February 12,1809 in Shrewsbury, England whose Scientific theory of evolution by natural selection became the foundation of modern evolutionary studies. An affable Country gentleman, Darwin at first shocked religious Victorian Society by suggesting that animals and humans shared a common ancestry. However, his non-religious biology appealed to the rising class of professional scientists, and by the time of his death evolutionary imagery had spread through all of science, literature and politics.

DARWIN’S JOURNEY THROUGH EVOLUTIONARY THEORIES:-

The belief that God had created mankind in his own image and likeness were shed by most western scientists until the middle of the 19th century when they thought that all the creatures of the planet had been conceived by a divine force that is until Charles Darwin arrived. Some researchers were already talking about an evolution of the species but the British Naturalist was the first to explain with evidence how evolution might occur by natural selection.

Darwin’s theory radically changed biology offering a new explanation of the origin of Human Beings. It also made him one of the most influential scientists and intellectuals in history but to get there he had to make an extraordinary journey, fighting all the odds before hundreds of experiments and spend 20 years of his life refining all his ideas. In 1831, when Darwin was 22 years old and studying at the University of Cambridge was invited as a Naturalist to a great expedition. He boarded the HMS BEAGLE and spent almost five years travelling several continents starting in South America from which he brought back dozens of life specimens illustrations and fossils. These fossils gave him one of the first clues about evolution, for example observing the remains of a Milodon– a giant animal similar to the sloth. He thought that those similarities were probably not a coincidence, there had to be some kind of link.

When he stopped at the Galapagos Island, Darwin also observed some giant tortoises which lived in nearby islands but showed unique physical characteristics in each island. In the humid areas where vegetation was abundant the turtles had a short neck and a dome-shaped shell whereas in the islands with a drier environment they had a saddle like shell along neck but he couldn’t explain that difference. Upon his return Darwin spent time observing how animal breeders and guards crossbred animals of species to create new varieties. For that creation to be successful the artificial selection made by man was key. Darwin realized that the natural world probably made the same kind of selection but he couldn’t explain how it happened until he read the work of Thomas Robert Malthus, a British intellectual from the 18th century. In an essay on demography, Malthus said that as the population in Europe was growing at one point it would increase much more than the food supplies available and that would cause a fight for survival. This idea helped Darwin explain how evolution works in nature. There is a struggle for survival in which the strongest individual is not necessarily the survivor instead it’s the one which best adapts to the environment where it lives. If a living being has any trait that helps them to survive it will be more successful at the reproduction. Those which don’t adapt will die without descendants. The creatures with the most success in reproducing, past their traits- their lineage and so on until these variations end up becoming a new species. That’s why the differences between the Galapagos Tortoises were a product of evolution.