History of Evolutionary Thought
What is an extant species?
A species that is still living
What is the difference between microevolution and macroevolution? Give examples of both.
Micro: change in the genetic composition of a population across short time scales
Pesticide resistance; Antibiotic resistance
Macro: change in the composition of species over longer periods of time
Mutation, gene flow, genetic drift, etc + many many year à macroevolution
Define what an obligate and a facultative trait is.
Expression of an obligate is determines by genes only
Expression of a facultative trait is determined by genes and the environment
In the Hardy-Weinberg equilibrium equation (p+q)2=p2+2pq+q2
what does p^2 represent?
Frequency of individuals who are homozygous dominant
What are the two types of reproductive isolation?
Prezygotic barriers: individuals never mate
Postzygotic barrier: mating occurs but offspring are not viable
What is adaptive radiation? What example of adaptive radiation did Darwin witness on his voyages?
The diversification of species originating from a common ancestor to fill a wide variety of ecological niches.
Finches!
What is a fossil and what benefit do they provide for us in studying evolutionary biology?
A fossil is any remains of an organism that lived in the past.
They reveal time scales for evolutionary events within a group of organisms. They can be used to test evolutionary hypotheses
How does variation in a population come about?
Mutations (errors during cell division, exposure to mutagens) and sexual recombination (crossing over, independent assortment, and fertilization)
The recessive allele (a) occurs with a frequency of 0.8 in a population of unicorns that is in HW equilibrium. What is the frequency of homozygous dominant indivuduals?
1-0.8 = p
p^2 = 0.04
Which species concept is used by paleontologists to help identify fossils?
Morphospecies concept
What's the difference between catastrophism and uniformitarianism, and how do these terms relate to evolution?
Catastrophism is a mechanism of extinction (proposed by Cuvier) by which large numbers of species are wiped out by a large catastrophe.
Uniformitarianism establishes that big things can occur over very long periods of time. Changes are slow and constant.
What is a transitional form? State its significance and give an example.
Species that have characteristics of both ancestral and modern species
Transitional forms provide evidence that intermediary organisms existed between extinct and extant species
Transitional forms contain a mix of characteristics from extinct and extant to help us understand how certain character traits may have evolved over time
What are the 3 main modes of selection? Define and provide examples of each.
Directional, stabilizing, and disruptive
List all 7 Hardy-Weinberg assumptions
No selection (no trait is beneficial over another)
Mating is random (no selection for a specific type of mate)
Population is large enough that there are no chance events that can change allele frequencies (no genetic drift)
No gene flow (no mixing from other populations)
No mutation
Everyone produces the same number of offspring
All members of population breed
What are 4 disadvantages associated with the biological species concept?
Mating or lack of mating hard to observe
Ability to mate versus likelihood to mate
Can not be applied to fossils
Not applicable to asexual populations (eg bacteria)
What was the mechanism proposed by Lamarck for why organisms in the fossil record are different from present day organisms?
Lamarckism: inheritance of acquired characteristics
Change in environment changes the need/use of a structure, causing it to change or shrink. Classic example: giraffes had to stretch to get more food, causing them to develop longer necks, which was inherited by their offspring.
This is the INCORRECT mechanism, but influenced Darwin in his proposal that evolution is driven by environmental changes over long periods of time.
Define and give 3 examples of vestigial organs.
Functionless or rudimentary organ in one species that has important function in other species
blind cave-dwelling organisms, human tailbone, flightless wings on birds, goosebumps
Natural selection is a blend of what two things?
Chance (creating new genetic variants by mutation) and sorting (relative fitnesses – differential survival of phenotypes)
What are the three evolutionary milestones during the Precambrian period?
Increase in O2 levels
Eukaryotes appear for the first time on Earth
Multicellularity arises for the first time
How do snapping shrimp species serve as an example of vicariance?
For each species of shrimp in the Pacific, its closest relative is in the Caribbean. This means that when the isthmus of panama was formed, it separated species that previously were able to flow freely from the Pacific to the Caribbean. populations were separated by a physical barrier, which led to reproductive isolation and divergence of two populations
What were the main ideas behind Thomas Malthus' economic theories on the principle of population?
There are competitions among humans for necessities of life
Increases in population would outgrow increases in the means of subsistence
Rapid growth in population would inevitably lead to disaster
State the 3 different types of homologies we studied in this course. Define and provide an example of each one. How do homologies differ from analogous structures?
Structural homology (mammalian forelimbs, stingers in bees and wasps)
Developmental homology (Vertebrate embryos all have something similar to gill slits of fishes and tail remnants)
Molecular homology (genetic engineering of crop plants)
Organisms that have analogous structures did not descend from a common ancestor. They converged on a useful trait due to similar selection pressures in their environment
What type of selection do cichlid fish demonstrate? Explain.
Negative frequency dependent selection.
Have mouths that are twisted right or left so they can eat off other fish’s flank. When one is more present than the other, the food supply for the side of the prey they eat from becomes more limited. The fish with the mouth occurring less frequently now has a survival advantage (a higher fitness), so they will increase in frequency.
What is the endosymbiosis theory?
Mitochondria and chloroplasts used to be small prokaryotes living within larger host cells. (They were engulfed by larger cells).
Symbiotic relationship – each gained something. Mitochondria became site of cellular respiration. Chloroplast became site of photosynthesis.
Explain what polyploidy is and how this leads to reproductive isolation
Polyploid organisms contain more than two paired sets of chromosomes. Polyploidy is caused by a failure of cell division.
Gametes with different chromosome numbers are often incompatible for breeding, which means a polyploid plant can only breed with other polyploids