BI111 Lecture Notes - Lecture 9: Heritability, Medium Ground Finch, Allele Frequency

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1 Feb 2017
BI111- Lecture 9 January 23rd, 2017
Evolution Theory Before Darwin: Lamarck’s Contributions to evolutionary thought
Species change over time
Change pass on from one generation to the next
Organisms respond to environmental conditions
Hypothesized mechanism (Principle of use and discus and principle of inheritance of
acquired characteristics)
Darwin’s Voyage
Darwin partook on the HMS Beagle which took about 5 years and exposed him to a huge
Stopped at the Galapagos island
1. Observation: Populations have great capacity to grow, but are ultimately limited by
resource availability (Shelter, Food)
o Inference: Competition between individuals in a population for resources
2. Observation: Individuals vary within populations in heritable traits related to
competitive success (Ultimately survival!)
o Inference: Some individuals will do better due to their phenotypic traits (More
likely to survive and reproduce than others)
3. Observation: Individuals may also vary within populations in heritable traits related
to reproductive competitive success
o Inference: Some individuals more likely to reproduce than others
Descent, with Modification
Adaptive Evolution: A population’s characteristics change over time, as advantageous
traits become more common
Although evolution experiences selection, there are changes of alleles which cause the
individuals with higher fitness and reproductive success to remain for longer periods of
Darwin’s Finches
Finches flown out to sea from Ecuador, isolated from the main land
Population has ability change based on environment parameters and become better
specialized to use different resources
Endemic- Species found there and nowhere else
Large-Ground finches- Died off second year during the drought because there were no
new seed beds (10+ to 3 grams)
What was there to Eat?
A variety of seeds are produced on the island, but finches prefer on the softest seeds, (the
easiest to open)
During the drought, the hardest seed on the island is produced by the Caltrop and it took a
medium ground finch with a beak at least 11mm long to open one because they don’t
have enough muscles in their beak to be able to grab them
o Decrease in resources and lack of soft seeds (Effect of form and function)
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