Charles Darwin
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Charles Darwin is credited with forming our modern evolution theory over 150 years ago; which he called Descent with Modification using the method of Natural Selection. His most widely known example that he used are the finches from the Galapagos Islands, often coined Darwin's finches.
He put together the pieces while sailing around the world on a five year voyage on the HMS Beagle. It was during this trip when he noticed the diversity of finches varies greatly at the Galapagos Islands. He studied 13 varieties, all of which varied from each other and from mainland finches. Influenced by Lyell, he knew that these island were relatively newly formed and concluded that the birds would have had to evolve somewhat recently.
He investigated further for years until eventually publishing his findings in his book On the Origin of Species by Means of Natural Selection. This brought him an onslaught of religious backlash from those who firmly believed that man hadn't changed since creation, but the scientific community quickly accepted his ideas because of the plethora of examples and evidence he had accumulated.
He put together the pieces while sailing around the world on a five year voyage on the HMS Beagle. It was during this trip when he noticed the diversity of finches varies greatly at the Galapagos Islands. He studied 13 varieties, all of which varied from each other and from mainland finches. Influenced by Lyell, he knew that these island were relatively newly formed and concluded that the birds would have had to evolve somewhat recently.
He investigated further for years until eventually publishing his findings in his book On the Origin of Species by Means of Natural Selection. This brought him an onslaught of religious backlash from those who firmly believed that man hadn't changed since creation, but the scientific community quickly accepted his ideas because of the plethora of examples and evidence he had accumulated.
Erasmus Darwin, Alfred Russel Wallace, and Jean Baptiste Lamarck
Erasmus Darwin believed that all organisms evolved over time but he didn't know how and had no evidence to support his claim. While he never spread his ideas to the public, he deeply influenced his grandson, Charles.
Alfred Wallace sailed to South America and developed the same theory as Darwin at about the same time. He also observed animals from around the world looking for evidence. He helped Darwin by sending him birds, and when he asked for help in publishing his own ideas, it turned out they had nearly the exact same theory. Unfortunately for Wallace, his proof perished when his ship sank, and Darwin was given sole credit when they presented the theory together. Jean Baptiste Lamarck was the first to propose a structure for evolution, though we now know it is flawed. Called the Inheritance of Acquired Characteristics (or simply the Use-Disuse Theory), it proposed that the more an organism and it's ancestors used a structure, the better developed it became over time. He used giraffe necks as an example, explaining how those who ate bushes had short necks and those who needed longer necks to reach trees grew taller. However, we know this is wrong because a man who lifts weights does not necessarily produce a strong baby, nor does an amputee produce a child missing a limb. Just because most of us are right-handed does not mean our left hands shrivel up and fall off from disuse. |
Theory of Evolution: Decent with Modification by Natural Selection
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Charles Darwin (and Alfred Russel Wallace) formed the theory of evolution, naming it Descent with Modification. It is the idea that all living and non-living things change over time using the mechanism of Natural Selection.
Darwin proposed five main ideas with his theory:
Evolution starts with a small change from the environment. A butterfly effect happens, and life must now adapt or die. The organisms least suited to the new environment die but the most capable live and reproduce, passing on their good genes. Eventually something changes again, and more revision takes place as a response. This is evolution at work, a gradual and continual process that has been occurring for more years than a human brain can fathom. (To see my small Prezi on this cycle, click here. To read more about Darwin's theory in greater detail, click here.)
Darwin proposed five main ideas with his theory:
- In nature, more offspring are produced than can possibly survive
- This overabundance creates a 'struggle to survive'
- There is variation of traits in all populations
- Populations with variations that give them an advantage are more likely to survive than those without the variation (survival of the fittest)
- Those who survive will mate and the favourable trait is passed down (natural selection)
Evolution starts with a small change from the environment. A butterfly effect happens, and life must now adapt or die. The organisms least suited to the new environment die but the most capable live and reproduce, passing on their good genes. Eventually something changes again, and more revision takes place as a response. This is evolution at work, a gradual and continual process that has been occurring for more years than a human brain can fathom. (To see my small Prezi on this cycle, click here. To read more about Darwin's theory in greater detail, click here.)
There were two problems Charles Darwin faced when explaining his theory, but were actually solvable at the time.
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Micro-evolution
Micro-evolution refers to the genetic changes within one species. All members of the species undergoing the same micro-evolutionary process will be able to breed and produce viable and fertile offspring. There are five ways the gene pool can change: Natural Selection, Mutations, Genetic Drift, Gene Flow and Non-random Mating.
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Very little of evolution is random, most of it changes the way it does so that the fittest organisms are the ones who reproduce. They contribute the most and best genes, meaning their offspring will be better adapted to the environment. If certain similar traits increase chances of survival, those traits will end up the most represented in the population. We know it is still occurring because we know our DNA is changing. We find fossil evidence that also shows the past changes within a species. Mutations cause the least change but gene flow, genetic drift and natural selection can greatly affect the population's gene pool.
There are three ways selection can influence the most frequent genes - stabilized, directional and disruptive.
There are three ways selection can influence the most frequent genes - stabilized, directional and disruptive.
- Stabilized Selection works against extreme variations and helps the middle of the spectrum become the average, causing a loss of genetic diversity and extreme variations increasingly rare.
- Directional Selection is when one extreme is favoured over the average, causing a new average to develop.
- Disruptive Selection is when the middle of the spectrum or gradient is disfavoured, and the extremes grow most common.
From what I have been able to find, Darwin supplied the idea behind micro-evolution (and macro-evolution) in his book On the Origin of Species by Means of Natural Selection but did not officially call it that. Instead, Russian entomologist Yuri Filipchenko used the term(s) in his German language work and it was later brought to anglophones by Theodosius Dobzhansky in his book Genetics and the Origin of Species.
Macro-evolution
Macro-evolution is very similar to micro-evolution, but instead of the changes occurring in the entire species they cause new species to form and branch out from one common species.
To see my references used in this unit, click here.
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Please let me know if any of my links and/or page elements are broken and I will fix them :)