Greek philosophers believed that all organisms were perfectly suited to their environment and they were organized by a scale of complexity called “scala naturae”. Then many people believed in creation that all organisms were made by god for a certain purpose. George Curvier believed that all changes in living organisms happened because large natural disaster killed off certain species but no new species were being created “Catastrophism”. James Hutton believed that everything changed gradually and the same mechanisms of change were still operating “gradualism”. Charles Lyell proposed uniformitarianism was influence by Hutton said that there was a constant level of change in the geological features of the earth. This meant the earth had to be very old and influenced Darwin in his idea of evolution being changes with species over time. Lamarck believed in a sort of evolution but he believed that the characteristics organisms obtained during their life could be passed along and the features not used would get weaker with the generations.
What is Darwin’s general theory?
Natural selection/ descent with modification
He believed that most organisms would reproduce until they overused their environmental resources and therefore those best suited to their environment would have a better chance of surviving to pass along their inherited traits to offspring. Because of this certain traits would become more prominent while others would leave a population. A population was the smallest unit of evolution and this also meant that all creatures were related to each other by a common ancestor.
What are Homologous structures, analogous structures and vestigial organs?
Homologous structures are structures that are the same in different species but they have different functions this shows a common relationship between all life. Vestigial structures have little to no use in a species but they are left over from their ancestors so they are still present. Analogous structures shows no relationship between organisms but are rather similar structures that arose from different species evolving to similar environments separate from each other.
Facts:
- Covergent evolution- is when organisms evolve separately to similar environments
- Biogeography- the geographic distribution of species this gives a lot of evidence for evolution
- Endemic species are those found only in a specific location and nowhere else in the world (typical to islands)
- Artificial selection- when humans breed animals for desired characteristics
- Darwin believed in decent with modification and because everything came from a common ancestor it could be organized into a tree of life
This shows how the same bones are used for different functions amongst mammals the homologous structures also show that all mammals are related in some way all the way from the bat to the human.
Summary:
There were many different theories about life on earth and the changes of the earth itself. The theory of evolution had been proposed by Darwin came up with a mechanisms through which it would be plausible. He went on a voyage in the Beagle and studied the birds on the Galapagos Islands and their common relation to each other and came up with the theory of natural selection. Much evidence such as fossil record, direct observation (bacterial resistance to drugs), homology, and biogeography supports the theory of evolution.
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