Lecture 7 - The Basis of Evolution by Natural Selection Flashcards
What are the three possible theories for the history of life?
Evolution
Transformation
Separate creation
What is evolution?
A change in gene frequencies over time
What are the 4 kinds of evolution
- Mutation
- Natural selection
- Genetic drift
- Founder effects
What is mutation?
The source of genetic variation
What is natural selection?
The sifting of variation to produce adaptions
What is genetic drift?
Random sampling of individuals over time
What is founder effect?
Small group of individuals “bud off” or survive by chance
What do mutations drive and innovate
New alleles in the generation
What evidence is there for evolution?
- The fossil record
- Observations of similarities and differences BETWEEN living species
- Evolution in action - Observing changes in real time
What are present continuously in the fossil record?
Intermediate forms
What does the order of fossils suggest?
Evolutionary relationships
- If you dig into the earth, there is an order of things. In different zones you can find different levels of complexity.
What are analogous species?
One that has evolved independently as a solution to a problem
What are homologous species?
Evolved through decent with modification
Example of an analogous species
Octopus: Inverted retina of vertebrate (left) and non-inverted retina of octopus (right). An example of totally separate evolutionary pathways
What are vestigal structures?
They suggest evolutionary descent.
- Pectoral and pelvic articulations are homologous in tetrapods; where the limbs are no longer adaptive, they have been lost but remains can still be seen in the skeleton
Example of a vestigal structure
Appendix is not needed anymore. It was a past adaptation from when we had high cellulose diets
What are phylogenetic approaches?
Understanding evolution by comparing features if extant species
What are two problems with evolutionary classifications based on external features
- Discriminating features
- Convergent evolution
What is convergent evolution?
Independent evolution of similar features in species. Creates analogous structures that have similar form or function but were not present in the last common ancestor of those groups
What are phylogenetic approaches?
the study of the evolutionary relatedness among groups of organisms.
What generates variations?
- Random mutations
- Recombinations (via sex)
- Gene flow
How many mutations were you born with?
- 300 of which at least 1 or 2 are potentially harmful if they are homozygous
- Over 10000 human genes have been described that in their mutated form cause diseases or defects.
- Variation is the building block for evolution
What are recombinations and variations?
- All genetic variation owes its origin ultimately to mutation.
- However in the short term recombination accounts for a great deal of the genetic variation in wild populations.
What factors can cause allele substitution in a population?
Natural (sexual) selection and genetic drift.
What is genetic drift?
Most populations are a finite size and random fluctuations in allele frequencies can result in the replacement of alleles (non-adaptive evolution)
What is effective population size?
The effective size (Ne) of a population is the number of adult individuals in the population that actually reproduce.
What are the implication of drift for metapopulations?
- Demes that initially are genetically identical evolve by chance to have different genetic constitutions.
- This assumes that the two alleles have identical effects on fitness (i.e. they are neutral).
What are founder effects?
- Populations that go through a restricted size are said to have gone through a bottleneck.
- This can happen when new populations are founded.
How does natural selection variations arise and why are individuals so well adapted to their environment?
Designing agent = Selection
- Acts to sift variants of behaviour, favouring those that provide their bearer with greater representation in the next generation
Selection for survival steps
- Huge numbers of individuals are produced
- Insufficient resources for all, so many die before reproducing
- Individuals vary in attributes
- Individuals with attributes better suited to environment are less likely to die
- These individuals will be over represented in next generation
Selection for reproductive share “sexual selection”
- Individuals differ in their reproductive output
- May depend on fecundity – number of offspring they can produce themselves
- May depend on attractiveness – number of mates they can obtain and the sum of THEIR offspring
What is the red queen hypothesis?
- Species (or populations) must continually evolve new adaptations in response to evolutionary changes in other organisms to avoid extinction.
- The term is derived from Lewis Carroll’sThrough the Looking Glass, where the Red Queen informs Alice that “here, you see, it takes all the running you can do to keep in the same place.”
