Sunday 22 April 2007
The Evolution Expert (Professor Carolyn Lesmana)
Charles Darwin’s theory of Evolution by Natural Selection
Charles Darwin was a British scientist. He formulated the theory of evolution by natural selection and released his findings in his book ‘the origin of species’. He changed the way we think about the natural world through science.
Theories before Charles Darwin’s theory
Before Charles Darwin released his book ‘ the origin of species’, several ancient philosophers have come up with their own theories. They had come up with the thought that Nature produces a variety of species in random order and that those creatures survive and provide for themselves and reproduce successfully.
Darwin’s Theory of Evolution
Darwin’s Theory of Evolution can be summarized into four main parts:
1) The world is ever-changing. Thus, organisms that have lived in the past might be extinct today. Over time, organisms have changed from the past and this can be proved through fossil records.
2) All the organisms come from the same ancestor through a process called branching. Over time, populations of species which are different but are related come from the same ancestor. Hence, different species which are classified together might have similar characteristics because they share the same traits from the common ancestor in the past.
3) Change occurs at a slow and gradual rate and it takes place over a long period of time.
4) The mechanism of Evolution is Natural Selection. Charles Darwin came up and formulated this theory after his observations he made on the Voyage of the Beagle.
Darwin’s Reasoning of Evolution by Natural Selection
- Organisms produce offspring. If the offspring continue to reproduce, then the existence of all organisms would be more than what the Earth can support
- As a result, organisms would fight for survival and only a few would ‘survive’. Different organisms would have different characteristics that determine their chances of survival. Even different organisms in the same population have different traits.
- Parents tend to pass on whatever traits they have to their offspring, but not in proportion. These traits are inclusive of the traits that determine their survival. Since the offspring resembles their parents, the next generation will have a higher proportion of individual that have the traits their parents had passed down to them.
What is Natural Selection?
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Over the ages, reproducing organisms have evolved through many generations. With each successive generation, organisms have adapted to the changing world, inheriting favorable traits which benefit them to continue to exist. This is called natural selection.
Evolution by Natural Selection:
Natural selection acts on the phenotype, or the observable characteristics of an organism, such that individuals with favorable phenotypes are more likely to survive and reproduce than those with less favorable phenotypes. If these phenotypes have a genetic basis, then the genotype associated with the favorable phenotype will increase in frequency in the next generation. Over time, this process can result in adaptations that specialize organisms for particular ecological niches and may eventually result in the emergence of new species. (taken from wikipedia’s definition of natural selection)
Key ideas of Natural Selection:
- it occurs between individual and environment organisms.
- Organisms have different traits, characters and abilities which allow them to survive and reproduce.
- Organisms will usually produce more offspring that can survive
- Heritable variations exist within populations of all species.
What examples were used to support his theory?
Examples of moths
During a time of industrial revolution, tree trunks were covered with soot. Tree trunks were the home of light-coloured and dark –coloured moths. However, since it was covered with sot, light-coloured moths were more easily seen than dark-coloured moths. Hence, they became an easier prey for the birds. During this period, the number of light-coloured moths decreased while the number of dark-coloured moths increased.
Example of flinches’ beaks
In 1977, the island of Galapagos was encountering a drought. Ecologists Peter and rosemary Grant observed that finches with small, soft beaks tended to get tired easily as they were not strong enough to eat big and tough seeds. In contrast, finches with strong and deep beaks were able to crack the seeds easily. Hence, they noted that the offspring of the birds that were able to survive the drought were mostly finches with deep strong beaks.
However, when the rainy weather came during 1984, it brought soft seeds. Thus, the Grants noticed that the number of finches with smaller beaks increased.
Bibliography
- Wikipedia.com
- http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html
- Evolutionhappens.net/
- Biology One (book)
Posted by evolutionrocks at 03:28