Lecture notes
4. Evolution and Origin
- Module
- Biology 1B
- Institution
- University Of Glasgow
Evolution and origin Topic within Biology 1B
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Evidence for EvolutionSummarise the evidence that led Darwin and Wallace to propose the theory of evolution by
natural selection
Darwin
Darwin noted that although the finches were very similar in size and appearance, there were distinct
differences in the sizes and shapes of their beaks. Darwin theorized that the beaks were adaptations
that helped each species of finch eat a different type of food, such as seeds, fruits, or insects. Some
finches had stout beaks for eating seeds; others were insect specialists. Darwin realised that they
were descendants of a single ancestor, and as they dispersed to different islands, the birds had
adapted to eat the various foods available on these islands, resulting in 13 different species.
Aided by his study of the Galapagos finches, Darwin developed his theory of natural selection, a part
of the larger process of evolution. The ‘fittest’ animals or plants – those with the characteristics best
suited to their environment – are more likely to survive and reproduce. They pass on these desirable
characteristics to their offspring. Gradually those features become more common, causing the
species to change over time. If the changes are great enough, they could produce a new species
altogether.
Wallace
In 1854 he began traveling through the Malay Archipelago (now Malaysia and Indonesia).
Throughout his eight years there, he collected a total of 125,660 specimens, including more than
5,000 species new to science! He also noticed a distinct pattern in the distribution of animals
throughout the archipelago. He proposed an imaginary line dividing the region in two major parts,
with Borneo, Bali and Java to the West of the line and Sulawesi and Lombok to the East. Later known
as Wallace’s line, this marked the boundary between the animal life of the Australian region and that
of Asia.
Together
Wallace saw that species changed because the fittest individuals survived and reproduced, passing
their advantageous characteristics on to their offspring. Wallace immediately wrote to Charles
Darwin, knowing he was also interested in this subject. And although Darwin had been working on
the very same theory for twenty years, he was yet to publish. Darwin was understandably surprised,
and although he had the means to claim the theory as his own, invited Wallace to present their
theories together at a Linnean Society meeting.
They proposed two theories of evolution:
1. The living organisms we see today are all related by descent (common ancestry)
2. The means by which evolution occurs is a process of ‘natural selection.’
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