Lecture 3: History of Evolutionary Thought Flashcards
Darwin and Evolutionary Thinking before the Modern Synthesis
one of the most influential texts of this century.
Origin of Species by Charles Darwin
What was Charles Darwin’s initial career pursuit?
Medicine
Where did Charles Darwin study botany?
Christ’s College, Cambridge
Who encouraged Darwin to join the Voyage of the Beagle?
Rev. John Henslow
Which ship did Charles Darwin embark on for his scientific expedition?
HMS Beagle
Who and what was Charles Darwin’s father and grandfather’s profession?
- Richard Darwin (father)
- Erasmus Darwin (grandfather)
- Doctors
What subject did Charles Darwin pursue a passionate interest in while at Christ’s College, Cambridge?
Natural History
Where did Charles Darwin make a major find of fossil bones during his voyage?
Punta Alta, Patagonia
What expertise did Darwin have during the voyage?
Geology
beetle collecting
marine
invertebrate dissection
Where are the Galapagos Islands located?
Pacific Ocean, west of continental Ecuador
What did Darwin conclude about the populations of species on the Galapagos Islands?
They descended from a common ancestor and were evolving.
What did Darwin question after observing the populations on the Galapagos Islands?
The stability of the concept of a “species.”
where did Darwin first observe mockingbirds that sparked his interest?
Galápagos, near Sappho Cove on Chatham Island (now Isla San Cristóbal)
What did Darwin notice about the mockingbirds on different islands in the Galápagos?
They differed slightly in size, shape, and coloration.
Who informed Darwin that tortoises also differed from island to island in the Galápagos?
Nicolas Lawson, acting Governor of Galápagos
What did Darwin speculate about the distribution of mockingbirds and tortoises towards the end of the voyage?
Their distribution might undermine the stability of species, suggesting that species are not fixed entities but change over time.
What did Darwin conclude about the mockingbirds after observing them on different islands?
They must have shared a common ancestor and were not independently created.
What did exposure to animal diversity during the voyage lead Darwin to conclude about species?
1) “Species” are not immutable fixed entities
2) Organisms are related by common ancestry (tree-like branching)
3) They are changing and branching in response to the environment (“Adaptation”)
Who did Darwin marry upon his return to England?
Emma Wedgewood
What historical developments provided the scientific context for the development of Darwin’s theory of evolution?
Discoveries in geology, including the understanding that the Earth is older than previously thought, and the fossil record showing changes in species over time.
What influential scientific theory did Lamarck propose before Darwin?
The inheritance of acquired characteristics.
Who influenced Darwin’s idea of competition and the struggle for survival?
Thomas Malthus, through his work “Essay on the Principle of Population.”
What idea did Darwin develop from Malthus’ work?
The concept of competition and the “struggle for survival” as components of natural selection.
Who independently came up with the idea of natural selection around the same time as Darwin?
Alfred Russel Wallace
What did Darwin and Wallace decide to do after learning about each other’s work?
joint presentation at the Linnean Society in 1858.
What was the title of Alfred Russel Wallace’s manuscript that he sent to Darwin?
“On the Tendency of Varieties to Depart Indefinitely from the Original Type”
When did Darwin publish “On the Origin of Species”?
1859
What are Darwin’s main points in “On the Origin of Species”?
1) Organisms evolve
2) Common descent: species arise from common ancestors
3) Gradualism: changes occur gradually
4) Population speciation: change in proportions of individuals with a trait in a population
5) Natural selection as the mechanism of adaptive evolution.
What was Lamarck’s view on the pattern of evolution?
Linear progression, often depicted as a “ladder of life” or “great chain of being.”
How did Darwin view the pattern of evolution?
As a tree-like branching process.
What was Lamarck’s proposed mechanism of evolution?
Inheritance of acquired traits at the individual level.
What was Darwin’s proposed mechanism of evolution?
Evolution at the population level via natural selection.
What is the problem with the “ladder of life” concept in Lamarck’s view of evolution?
It implies progress and a linear progression, which is not consistent with the branching nature of evolution.
What were some limitations of Darwin’s theory of evolution?
- Because Darwin knew nothing about mutation, he had no idea how variation was generated in populations
- Because Darwin knew nothing about genetics or genes, he had no idea how variation was passed on to offspring (Mendel & Hardy-Weinberg)
- Darwin did not know about nonadaptive evolutionary forces, such as Genetic Drift
What did Mendel’s work provide a mechanism for in terms of inheritance?
How traits are passed on from parents to offspring, through the idea of particulate (gene) inheritance.
When was Mendel’s work initially published, and when was it rediscovered?
Mendel’s work was published in 1865 but was ignored until it was rediscovered in 1900.
Who were the scientists credited with rediscovering Mendel’s laws of inheritance?
- Dutch biologist Hugo de Vries
- German plant geneticist Carl Correns
- Austrian plant breeder Erich von Tschermak-Seysenegg.
What mathematical concept, related to Mendelian inheritance, did Hardy and Weinberg develop?
The Hardy-Weinberg equilibrium, which describes the mathematical expectations of Mendelian inheritance and whether those expectations are realized in nature.
Mendel and Darwin’s ideas seemed Incompatible
* Mendel’s principles: dealt with __ (e.g. __, __)
* BUT, Darwin observed __ (e.g. __, __)
- particulate (discrete) traits
–> yellow vs. green
–> wrinkled vs. smooth - continuous traits
–> beak size
–> body length
Mutations discovered after __
1900
They thought that evolution required only mutations and passing on of discrete traits
Mutationists (+ Mendelianism)
They thought that evolution required only Natural Selection on continuous variation
Darwinists
Darwin was unable to clearly see the pattern of inheritance because he studied __
quantitative variation
Darwin did not understand the __ (what is being inherited, genes)
unit of inheritance
a trait that has distinct values, rather than a range of phenotypes, usually encoded by one or a few genes.
distinct trait
examples of distinct traits
- number of fingers
- color of Mendel’ s peas
- sickle cell anemia
- ABO blood type
- number of eggs in a bird clutch
- presence/absence of human widow’s peak
- presence/absence of dimples, etc.
a trait that has a continuum of phenotypes and is encoded by multiple genes.
Quantitative (continuous) trait
examples of Quantitative (continuous) trait
body size
Height
Weight
intelligence (IQ)
Running speed
beak shape
hair color
skin color
milk yield of cows
lifespan, etc.
Proponents of the Darwinist Theory
Proponents of Darwinism were correct about mechanisms of __, but they did not understand what __ was acting on, as they were unaware of the __ or how the variation was passed on to the next generation.
- Natural Selection
- Selection
- unit of inheritance (genes)
Proponents of the Darwinist Theory
They came up with the idea of __ where offspring gain characteristics of both parents, like mixing colors of paint… but, this was a vague idea that was __
- “Blending inheritance”
- incorrect
Proponents of the Darwinist Theory
Many of them were __ (statistical types) that thought that evolution was gradually acting on continuous traits
Biometricians
Proponents of the Mutationist/Mendelist Theory
Many Prominent __ at the time supported the Mutationist/Mendelist theory
Geneticists
Proponents of the mutationist theory included __, among those who “discovered” Mendel’s 1900 paper.
Hugo de Vries
Proponenets of the mutationist theory included __, founder of Drosophila genetics
Thomas Hunt Morgan
Thought that evolution arose through genetic changes (mutations) that were discrete and sudden
Proponents of the Mutationist/Mendelist Theory
Proponents of the Mutationist/Mendelist Theory
New species originated when they mutated from pre-existing species, but this process was independent of __
natural selection
Controversy between Mutationists vs Darwinists
Controversy persisted for __ years up till the __, during which little progress was made
- ~30
- 1930s
Problems to Resolve
* At the heart was the question of whether __ and __ could be reconciled with mechanisms of __.
* A second issue was whether the broad-scale changes (__) seen by palaeontologists could be explained by changes seen in local populations (__).
- Mendelian genetics
- Mutation
- Natural Selection
- macroevolution
- microevolution
the mendelian and darwinism problem is caused by
- Binary thinking (Black or White thinking)
- Inability to see overarching mechanism
what could explain a wide range of phenomena, like “How could your Hardy-Weinberg (Mendel) explain the inheritance of 5.1 cm, 5.5 cm beak length (continuous characters)?”
overarching mechanism
A concept as important as Natural Selection
But, not as prominent on people’s minds
Genetic drift
When was The Modern Synthesis
1930s-1940s
The Modern Synthesis is also called
“Synthesis of Evolution and Genetics”
The Modern Synthesis
The synthesis of population genetics
integrate the roles of :
- mutation
- Selection
- genetic drift
- Paleontology
- Systematics
Darwin and Mendel Reconciled
The Modern Synthesis
Among the Greatest Scientific Revolutions of the Century
The Modern Synthesis
Three of the “architects” of the evolutionary synthesis:
- G. Ledyard Stebbins Jr.
- George Gaylord Simpson
- Theodosius Dobzhansky
__ was important because many scientists from different fields convened to discuss the evolutionary mechanisms and clear up confusion and inconsistencies
The Evolutionary Synthesis
Some Key Tenets of the Modern Synthesis:
Natural Selection and Mutation are not the only evolutionary forces. Give other examples:
Examples: Genetic Drift, Migration
Some Key Tenets of the Modern Synthesis:
are the units of Evolution
Populations
Some Key Tenets of the Modern Synthesis:
are sources of genetic variation upon which Selection acts
Mutations
Some Key Tenets of the Modern Synthesis:
Microevolutionary processes, such as __, __, __, lead to Macroevolutionary changes
- Drift
- Selection
- Mutation
Some Key Tenets of the Modern Synthesis:
Acquired characters (__) are not inherited
phenotypic plasticity
Some Key Tenets of the Modern Synthesis:
Traits are inherited via __, and they do not “__” with other genes (Darwin was wrong about this one)
- genes
- blend
Genes mutate, resulting in __
different alleles
Evolution occurs at the __, due to a change in proportions of individuals with different genotypes
population level
Changes in proportion in a population could occur via __ (Sewall Wright) or __… the rate of mutation is usually too low to cause large changes in proportions
- random genetic drift
- Natural selection
Even very weak natural selection could cause __ over a longer time scale
substantial changes
generate the genetic variation upon which natural selection acts
Mutations
Microevolutionary processes lead to Macroevolutionary changes
speciation
All organisms on the planet are related to one another in a great “tree of life”, and have diverged by branching from __
common ancestors
Gaps in the fossil record are likely due to incompleteness of the __ . Gradual changes seen in many parts of the fossil record suggest gradual changes over time
- fossil record
