Week 3 Flashcards
Describe Wallace’s influence on the theory of evolution.
Wallace was an early believer in transmutation of species (influenced by Lamarck and Malthus).
Wallace wrote Darwin in 1858 describing his theory.
The Origin of Species was published November, 1859, one year after the joint presentation of Darwin and Wallace’s essays.
List and describe each of Darwin’s five sub-theories to his theory of evolution.
(1) Evolution as such characteristics of lineages of organisms change over time
(2) Common descent (one shared ancestor)
(3) Gradualism
(4) Population variation
(5) Natural Selection
Describe how Darwin’s sub-theories differed from his predecessors’ ideas.
(1) Gradualism differs from saltations (large leaps without intermediate forms)
(2) Population variation differs from Platonic idealism (the views of Aristotle)
(3) Variational evolution and Natural Selection challenged Lamarckism/transformationalism
Describe what is missing from Darwin’s theory
Darwin’s theories lacked a mechanism of inheritance. Darwin believed in a blending inheritance, however this did not make sense with the other sub-theories. If offspring phenotypes are intermediate between their parents, then this reduces variation across generations, which was a key factor in Darwin’s theory of evolution.
Describe what ideas were brought together by the Modern Synthesis.
Fisher, Haldane, and Wright showed that natural selection could operate with Mendel’s theory of inheritance using principles of population genetics.
Mayr proposed that population genetics theory applied to geographically separated species could explain speciation.
This gave rise to the Modern Synthesis or neo-Darwinism, which is a combination of Darwin and Mendel’s findings.
Describe how Darwin imagined traits to be inherited.
Darwin believed in blending inheritance, which means the offspring phenotypes are intermediate between their parents.
In the early 1900’s, Mendelians and Biometricians subscribed to different beliefs regarding phenotypes and inheritance. Compare the ideas/concepts ascribed to each group.
Mendelians, led by William Bateson, studied large differences among individuals. They focuses on discrete traits and rejected the theory of Natural Selection. They believed evolution proceeded through a series of macromutations.
Biometricians, led by Karl Pearson and W.F.R Weldon, studied small differences among individuals. They focused on quantitative traits and supported the theory of Evolution by Natural Selection.
Summarize Edward East’s contribution to evolutionary science.
Edward East worked with long-flower tobacco, breeding short and tall phenotypes together.
Through these studies, East showed that relatively few loci are required to approximate continuous variation in a trait.
Name key historical figures associated with the Modern Synthesis.
R.A. Fisher, J.B.S. Haldane, Sewall Wright, Ernst Mayr
List and define the three conditions necessary for evolution by natural selection.
(1) Phenotypic variation: individuals in a population differ in the focal trait
(2) Heritability: phenotypic variation has a genetic basis
(3) Variation in fitness: focal traits influence lifetime reproductive success
Define two types of phenotypic variation and describe their modes of inheritance.
Discrete phenotypic variation: controlled by one or a few loci and one or a few alleles. Straight-forward predictions of cross-generational inheritance. (Mendel’s peas, Labrador coat colour, snow geese colour morphs)
Continuous phenotypic variation: controlled by multiple loci and alleles (also called polgygenic inheritance). The genotypes are unknown so we use statistical models ot predict cross generational inheritance, called quantitative genetics. (The majority of traits: height, mass, physiological function, longevity).
Define reaction norm and explain how it can help test whether or not a trait value is affected by the environment.
The Norm of Reaction is a set of phenotypic expressions of a genotype under different environmental conditions that produces a quantified conceptualization of phenotypic plasticity.
A steep line shows phenotypic plasticity because the individual trait value is changing significantly with the environment.
Thus, a flat line would mean no phenotypic plasticity.
Define permanent and reversible plasticity, and give examples of each.
Reversible plasticity are traits that can return to their ‘default’ or the expression they were before the environmental conditioning. An example would be the emergence date from hibernation of Columbian ground squirrels.
Permanent plasticity are traits that are determined by the environment and cannot be changed afterwards. An example of this is the sex of seas turtles determined by the temperatures of the eggs during incubation.
Define statistical means and variances, and understand how they can be used to describe phenotypic variation.
Mean is the average values (measure of central tendency) and variance is the averaged squared deviation of observations from the mean (a measure of spread).
If the mean changes, the overall curve moves.
If the variance is larger, we see a flattening out of the curve.
With juts the mean and variance, we can describe the entire distribution.
What is the primary ingredient for evolutionary change?
Intraspecific variation
selection + heritable genetic variation = evolution
Define phenotypic plasticity.
Capacity of a single genotype to develop any of several phenotypic states, depending on the environmental conditions to which its exposed.
True or false? Phenotypic plasticity can be adaptive or maladaptive or neutral.
True
