Introduction to Evolution Notes

Populations produce many offspring, but only some survive to reproduce.
Genetic variation leads to differences among individuals.
Individuals best adapted to the local environment leave more offspring.
Camouflage helps individuals avoid predators, increasing their survival and reproduction rates.
An individual does not evolve; a population evolves.

A group of organisms of the same species living together in the same geographic area.
An entire population can change (evolve) when some traits are favored over others.
The results of evolution are apparent in the offspring after several generations.
Evolution acts on populations, not individuals.
Evolution is a change in allele frequency in a population.

If Swedes migrate to Asia and interbreed with locals, the frequency of blond hair and blue eye alleles will increase in the Asian population over multiple generations.

Aristotle (350 BCE): Individuals in a species are basically identical and species are unchanging.
Buffon (1749): Species change as they spread from their original location.
Hutton (1785): Changes in nature are gradual; uniformitarianism.
Cuvier: Species reappear after catastrophes; fossils represent extinctions.
Lamarck: New species come from existing species through environmental forces.
Lyell: All changes in nature are gradual; renewed uniformitarianism.
Darwin & Wallace: Individuals in a population are different; species arise through the process of natural selection.

Born in 1809 and died in 1882.
Studied medicine at Edinburgh University at 16 but hated it.
Went to Cambridge University to become clergy.
Became interested in zoology, botany, and geography (influenced by Prof. Henslow).
Served as a naturalist on H.M.S. Beagle (1831-1836).
Began his voyage at 22 years old.
The initial 2-year survey of South America turned into 5 years.
His duties included collecting and identifying new species.

Darwin visited the Galapagos Islands.
He observed similar animals on various islands, such as finches and tortoises.
He did not develop his hypothesis of evolution while there but started thinking about the origin of species.

Darwin studied finches in the Galápagos Islands.
He believed that different finch species descended from the same finch ancestor.
He noticed that their beak types matched the foods they ate.
Darwin was challenged to insert these birds into the Linnaean classification scheme because he couldn’t identify species.

Observations of nature:
- Heritable variation: Individuals within a species are not exactly alike, and some variation is heritable.
- Limited resources: Every habitat has limited resources required for survival.
- Overproduction of offspring: More individuals are born than survive to reproduce.
Inferences from observations:
- Struggle for existence: Individuals compete for limited resources.
- Unequal reproductive success (natural selection): Inherited characteristics make some individuals more likely to obtain resources, survive, and reproduce.
- Descent with modification: Over many generations, a population’s characteristics can change via natural selection, potentially leading to new species.
Natural selection occurs when environmental factors give individuals with certain traits a reproductive advantage.

Chemicals that either kill bacteria or slow their growth.
Interfere with the function of essential bacterial cell structures.
Beta-lactams (e.g., penicillin) interfere with a bacterium’s ability to synthesize cell walls.
Osmosis ultimately kills the bacteria.

Enzyme $\beta$ -lactamase is encoded by a gene called bla. This gene can be passed to offspring.
Resistance to antibiotics is a heritable phenotype/trait.

Bacteria acquire random mutations when DNA replicates, or they can pick up genes from the environment.
They pass these genes to their offspring.
Humans do not become resistant to antibiotics.

Any bacterium that can resist an antibiotic is more likely to survive and reproduce.
This makes it harder to treat infections as bacteria become resistant to more and more antibiotics.

Organisms’ ability to survive and reproduce in a particular environment.
Higher fitness = increased likelihood of alleles being passed to the next generation.
Alleles that confer resistance to antibiotics increase an organism’s fitness.

The interplay between phenotype and environment determines the frequency of traits in a population.
If a trait improves fitness, the alleles that encode that trait become more common in the population.
Population evolves à Natural selection.