Lecture 2 & 3: Darwin's theory of evolution and processes of evolution Flashcards
What is the supernatural explanation of the diversity of earth’s living organisms?
There is one “true” form of each species. This uses typological thinking.
Believed Earth was only about 6000 years old
What are the organic views of the diversification of life?
Erasmus Darwin & Lamarck/ Charles Darwin
Erasmus Darwin: Theories were similar to LaMarck who proposed that organisms can change due to natural processes.
1. Species change gradually through time
2. Each species represents a stage in its evolution from a simple ancestor
3. Each new species arose through spontaneous generation from non-living matter
4. Characteristics acquired during an organism’s lifetime will be passed on to its offspring
5. No common ancestry
Charles Darwin: provided a plausible mechanism for how species changed over time
What are the five components of Darwin’s theory of evolution?
- Steady change: the world is steadily changing, species dont stay the same forever
- Gradualism: changes in species take place gradually
- Common descent: There was a single origin of life on earth and all species on earth have a common ancestor
- Natural Selection: Evolutionary change by perferential survival and reproduction of better adapted organisms
- Multiplication of species: Speciation! New species can evolve from existing species.
Natural selection is the only truly original component of Darwin’s theory of evolution.
What is natural selection and what are the four observations it was based upon?
Natural selection is the differential survival and reproduction of better adapted organisms. It is the mechanism by which evolutionary change occurs within a population.
- There is variation among individuals: some individuals vary in a way that increases chances of survival and reproduction
- Variation is heritable
- Species produce more offspring than can survive
- Differential reproductive success: successful individuals are more likely to survive and reproduce
What is fitness?
Fitness is the ability of an individual to produce surviving fertile offspring, relative to other individuals in the population
What is an adaptation?
An adaptation is a heritable trait that increases the fitness of an individual relative to another individual that lacks the trait.
Biston betularia is a British moth that comes in two different colors: a lighter (peppered) and darker (melanic) form
What was the mechanism of natural selection and what was Kettlewell’s hypothesis?
Natural selection of biston betularia occurred based around the industrial revolution, which put out smoke and soot that darkened trees.
Kettlewell’s hypothesis:
These moths spend a lot of time resting on tree trunks during the day. Before the industrial revolution, the peppered moths blended with the tree trunks and were less visible to predators. After the industrial revolution, the melanic moths were favored due to the darker trees.
Kettlewell proved this by testing that birds were predators of the moths and comparing the survival of melanic and peppered moths.
There are four types of natural selection: directional, stabilizing, disruptive, and sexual.
What is directional selection?
Directional selection occurs when there is a change of frequency that proceeds in one direction over time.
Example: Biston betularia (British) moths
Example: Bird population on an island in the Galapagos monitored by the Grants
Example: Cliff Swallows - put their own eggs in another swallow’s nest
There are four types of natural selection: directional, stabilizing, disruptive, and sexual.
What is stabilizing selection?
Stabilizing selection favors intermediate individuals and weeds out extremes.
Example: Baby weight - Babies that were too small and too big could not survive and have low fitness
Example: Ipomopsis agggregata plant - length of stamen cannot be too long or too short
There are four types of natural selection: directional, stabilizing, disruptive, and sexual.
What is disruptive selection?
Disruptive selection is quite the opposite of stabilizing selection and favors the extremes over the intermediate.
Example: Gill-raker fish - Less dense gills and more dense gills helped capture food but not in between
There are four types of natural selection: directional, stabilizing, disruptive, and sexual.
What is sexual selection? What are the two types?
Sexual selection occurs when there are differences in the ability to attract mates.
Intersexual selection: Females choose males based on some cue
Intrasexual selection: Male competition- males compete for territory or access to females
