Lecture 10. Natural Selection and Evolutionary Processes Flashcards
When is natural selection inevitable ?
- Replication
- Variation between individuals
- Heritability of traits
- Differential survival
What is differential survival ?
Only the individuals who do best in the environment, grow up and successfully breed
What conclusion can we draw about individuals who inherit traits which fit them well for their current environment ?
They are more likely to breed and pass on those good traits to their offspring
What does the frequency of the increase in good traits and reduction of bad traits result in ?
The population slowly changing to be better adapted to its environment
What is the evolution of the population ?
The inevitable outcome of replication, variation between individuals causing differential survival and heritability of the locally beneficial traits
What was Darwin’s problem of variation and inheritance ?
He did not know how traits passed from parents to offspring and he thought the traits of the parents blended in the offspring which gets rid of variation very fast. He also knew that variation is maintained much longer than blending would allow.
What theory did Darwin propose for his problem of variation and inheritance which turned out to be incorrect ?
Pangenesis
What is pangenesis ?
This theory says that variation acquired during the animals lifetime are transmitted to the germ cells by gemmules returning variation to the system.
What did Gregor Mendel do ?
Carried out breeding experiments with peas, and quantitative analysis of the resulting forms to infer how inheritance worked
What did Mendel’s genetic show us ?
- Inheritance through alleles of genes is particulate not blended. This maintains variation despite variation.
- Acquired characteristics are not inherited, so play no part in evolutionary change
What did Mendel’s genetics tell us about natural selection ?
Natural selection is the change in frequency of stable variants
Which scientists integrated all our evolutionary understanding into “The modern synthesis” ?
Ernst Mayer, George Ledyard Stebbins, Theodosius Dobzhansky
What does the “Modern Synthesis” reconcile ?
- Natural selection
- Mendelian genetics
- Population genetics
- Macroevolution
- Microevolution
What is macroevolution ?
Species level patterns in survival and extinction
What is microevolution ?
Individual level changes in populations of organisms
What does “The Modern Synthesis” theory agree with ?
That natural selection, working on heritable variation, supplied by mutation, brings about evolution
What does natural selection remove ?
Variance
What is punctuated equilibrium ?
New species are formed by leaps where whole organism changes occur
What do evolutionary scientists say how does evolution progress on the geological timescale ?
Punctuated gradualism
What is punctuated gradualism ?
Bouts of faster change when selection pressure are high, and variation is present. Slower or no change when less selection pressure or mutations are needed
What did Sheldon 1987 show ?
Evolution is gradual, but it varied in both rate and direction
What are the three types of selection over geological timescales ?
- Directional selection
- Stabilising selection
- Disruptive selection
What is directional selection ?
One extreme of the population is the fittest
What is stabilising selection ?
The mean of the population is the fittest
