Study Guide 3 Natural Selection Flashcards
describe how concepts from the field of geology influenced Darwin’s theory of evolution
Lyell’s gradualism– slow changes over long time periods (like erosion shaping the grand canyon). Drawin applied this to slow genetic and physical changes in organisms over time
how did Aristotle’s scala naturae differ from Darwin’s theory of evolution?
the scala naturae was hierarchical and didn’t include species change over time. Darwin focused on variety across groups and mechanisms driving species change over time
how did cuvier explain the disappearance of some lineages and the appearance of new lineages in the fossil record?
he believed catastrophes caused extinctions, and new species then migrated into the area afterward (catastrophism)
what is the difference between homologous traits and analogous traits?
-Homologous traits: result from shared ancestry; inherited and modified over time
-Analogous traits: evolved independently through convergent evolution; similar traits arise due to similar environmental pressures
determine whether the trait listed is homologous or analogous: limb bones of humans and cats
homologous
determine whether the trait listed is homologous or analogous: wings of birds and insects
analogous
determine whether the trait listed is homologous or analogous: streamlined body shape in dolphins and sharks
analogous
determine whether the trait listed is homologous or analogous: cactus spines and conifer needles
homologous
what are the necessary and sufficient conditions a population must meet in order for natural selection to occur?
-Variation: individuals in a population must have different traits
-Heritability: traits must be partially genetically controlled
-Differential Success: some individuals survive and reproduce more than others based on their traits
how is frequency-dependent selection similar to and different from directional selection?
-short-term: resembles directional selection; one phenotype has higher fitness, causing a population shift
-key difference: benefits arise from rarity, not the phenotype itself
-long-term: as a rare phenotype becomes common, its advantage decreases, leading the population to shift back to the rarer phenotype
under what conditions would altruism be supported by natural selection?
Altruism is favored when it enhances fitness by:
-Inclusive fitness: that benefits to close relatives can outweigh costs to the altruist
-Individual fitness: my help individuals gain mates or mating opportunities
-Population w/ cultural altruism: individuals expect to receive future support, making current altruistic acts worthwhile despite immediate costs
what type of factors constrain the process of natural selection? I.E. why does natural selection not always result in organisms that are ‘perfectly’ adapted to their environment”
-Laws of physics: E.G. insect body size limited by oxygen levels
-Evolutionary history: natural selection acts on existing variations shaped by past selection
-Tradeoffs: maximizing one trait may limit others or sustain energetic cost
-Lack of variation: What’s beneficial in an environment can vary over time and across benefits
Bacteria are asexual organisms, and a bacterium reproduces by duplicating its DNA and
splitting into two separate cells. If a single bacterial cell that is sensitive to vancomycin
(an antibiotic) is placed in an environment that contains vancomycin, it will die. Now
consider another single bacterial cell, also sensitive to vancomycin, that is allowed to
divide for many generations into a larger population. If this population is placed into
vancomycin-containing environment, some bacteria will grow.
a) why do you see growth in the larger population (that is allowed to divide), but not with the single cell?
-As bacteria divide, mutations occur, leading to genetic variation in the colony.
-Some of these mutations can provide resistance to vancomycin, allowing certain bacterial cells to survive in its presence.
Bacteria are asexual organisms, and a bacterium reproduces by duplicating its DNA and
splitting into two separate cells. If a single bacterial cell that is sensitive to vancomycin
(an antibiotic) is placed in an environment that contains vancomycin, it will die. Now
consider another single bacterial cell, also sensitive to vancomycin, that is allowed to
divide for many generations into a larger population. If this population is placed into
vancomycin-containing environment, some bacteria will grow
b) which of the populations meets the conditions for natural selection? what type of selection is occurring?
-A single bacterial cell cannot exhibit variation or differential success and is not reproducing.
-In contrast, a larger colony does meet these condition.
-Higher resistance to vancomycin is more beneficial, leading to expected directional selection towards increased vancomycin resistance
You are interested whether harvesting large fish from a population will select for smaller
body size. You create an experimental population of fish, all the same age. The average
body size of your experimental population is 100g. You then harvest the largest fish. The
average body size of the fish remaining in the population is 75g. The fish remaining are
allowed to breed. What is the predicted body size if heritability is:
a) 1
75
-This represents fully heritable, so the next generation has the same value as the fish remaining after selection
