Unit 1: Evolution - Natural Selection Flashcards
When did Darwin return to England?
In 1936
What did Darwin do when he returned to England
Wrote papers describing his collections & observations
What did Darwin bring back?
Brought back thousands of specimens and fossils
What came out in 1844?
A draft of his theory of species formation
What was Darwin concerned about?
The impact of his ideas in a religious culture
What did Darwin instruct his wife to do?
Instructed his wife to publish this essay upon his death
What was Darwin reluctant to do?
To publish but didn’t want ideas to die with him
What happened in 1858?
Darwin received a letter that changed everything.
Who was the letter from?
Alfred Russel Wallace, a young naturalist working in the East Indies
What had Alfred Russel Wallace done?
Had written a short paper with a new idea.
What had he asked Darwin?
To evaluate his ideas and pass it along for publication.
What happened on November 24, 1859?
Darwin published “On the Origin of Species by Means of Natural Selection”
What was Darwin’s first idea?
Variation exists in natural populations
What was Darwin’s second idea?
Many more offspring are born each season than can possibly survive to maturity
What was Darwin’s third idea?
As a result, there is a struggle for existence - competition
What was Darwin’s fourth idea?
Characteristics that are beneficial in the struggle
for existence will tend to become more common in the population, changing the average characteristics of the population - adaptations
What was Darwin’s fifth idea?
Over long periods of time, and given a steady input of new variation into a population, these processes lead to the emergence of new species
What was Darwin’s first observation (Darwin’s Theory of Evolution by Natural Selection)?
Individuals within a species vary in many ways
What was Darwin’s second observation (Darwin’s Theory of Evolution by Natural Selection)?
Some variability can be inherited
What was Darwin’s third observation (Darwin’s Theory of Evolution by Natural Selection)?
Each generation produces way more offspring than can survive and passes on variations
What was Darwin’s fourth observation (Darwin’s Theory of Evolution by Natural Selection)?
Populations tend to remain stable in size
What was Darwin’s first inference (Darwin’s Theory of Evolution by Natural Selection)?
Members of the same species compete with each other for survival
What was Darwin’s second inference (Darwin’s Theory of Evolution by Natural Selection)?
Individuals with more favourable variation are more likely to survive. SURVIVAL IS NOT RANDOM
What was Darwin’s third inference (Darwin’s Theory of Evolution by Natural Selection)?
Survivors contribute proportionately more offspring to succeeding generations the favourable variation will become more common THIS IS NATURAL SELECTION
Why did people not believe Darwin’s theory?
Not everyone thought the earth was millions of years old
What did fossil records have?
HUGE gaps (geology and palaeontology are new sciences)
What did fossil records now show?
Transitional forms
What did people not know about?
Genetics
What has life on earth been dated at?
3.5 billion years
Today, how many more fossils have been found?
Far more fossils found which show progression
What do we understand today?
Genetics, mutations, and recombination - this gives the most compelling evidence
What happened in 1866?
Gregor Mendel publishes work on peas (ignored until 1900s)
What came from the idea of Natural Selection?
Two results or theories (to further study)
What are these two results or theories called?
Descent with Modification
Common Descent
What is Descent with Modification?
Each living organism has descended, with changes from other species over time
What is Common Descent?
Were derived from common ancestors
What is Natural Selection?
A mechanism of evolution where by traits become more or less common in a population due to effects on survival and reproduction
What are the four types of natural selection?
1.Directional Selection
2.Stabilizing Selection
3.Disruptive Selection
4.Sexual Selection
What is directional selection?
Selection that favours an increase or decrease in the value of a trait from the current population; favours the phenotypes at one extreme over another.
What is stabilizing selection?
Selection that favours intermediate phenotypes and acts against extreme variants
What is one example of stabilizing selection?
Human babies have an average size
Too big and they can’t get through birth canal
Too small and they have low survivability
What is disruptive selection?
Selection that favours two or more variations of a trait that differ from the current population average
What can disruptive selection lead to?
New species forming
What is mimicry?
Similarity of one species to another which provides protection
What are some mimicry similarities?
Appearance, behaviour, sound, scent
What is sexual selection?
Differential reproductive success caused by variation in the ability to obtain mates
What does sexual selection result in?
Results in sexual dimorphism, and mating courtship behaviours
What is sexual dimorphism?
A phenotypic difference between males and females of the same species
What phenotypic differences result from sexual dimorphism?
Morphology
Ornamentation
Behaviour
What is one example of sexual selection?
Female Mate Choice: Females choose mates based on physical traits, such as bright colouration and behaviour
What is another example of sexual selection?
Male-versus-male competition = males have physical features that assist them in establishing control of and defending their territory used in direct competition
What are some changes in the genetic makeup of a population NOT?
Influenced by the traits of individuals
What are examples of evolutionary change without selection?
1.Genetic Drift
2.Bottlenecks and Founder Effect
What is Genetic Drift?
Changes to allele frequency as a result of chance are much more pronounced in small populations
What happens when populations are small?
Chance can play a significant role in altering allele frequencies.
What is a genetic bottleneck?
A dramatic, often temporary, reduction in population size, usually resulting in significant genetic drift
What is the founder effect?
Genetic drift that results when a small number of individuals separate from their original population and establish a new population
What is a human example of the founder effect?
Polydactyly (extra fingers and toes, a symptom of Ellis-van Creveld syndrome) are more common in Amish communities in the US
Why is Polydactyly more common in Amish communities in the US
This is because they have grown from a very few founders, have not recruited newcomers, and tend to marry within the community
