Where does evidence for evolution come from?
Paleontology, biogeography, embryology, Comparative anatomy, Molecular biology
Darwin’s arguments
Populations posses tons of reproductive potential, population sizes are stable, Resources are limited, Individuals compete to survive, Variation is a thing, much variation is heritable, only the fittest individuals survive, evolution occurs as favorable traits accumulate in the population
Stabilizing selection
Selects against the extremes
Directional selection
selects for one extreme
Disruptive selection
Selects for extremes
Sexual selection
Differential mating of males in a population. Example: peacocks, deer/antlers
Artificial selection
Directional selection carried out by humans
Balanced polymorphism
The maintaining of different phenotypes in one population. This can happen in several ways:
- Heterozygote advantage, like with sickle cell anaemia vs. malaria
- Hybrid vigor: when a hybrid is better than either of the two species it came from
- Frequency dependent selection: When the rarest phenotype has the greatest chance of survival, becomes common, and then is selected against, becomes rare…for example, predators that form a search image for the most common form of their prey.
Sources of variation (5)
Mutation, Sexual reproductions, diploidy, outbreeding, balanced polymorphism.
Neutral variation
Variation that has no selective value
How do humans impact the evolutionary potential of other species?
By creating environments in which monocultures are prevalent (agriculture), and overusing antibiotics, thereby eliminating the types of plants that are susceptible to the antibiotics.
Causes of changes in allele frequencies
- Natural Selection
- Mutations
- Gene Flow: movement of individuals between populations
- Genetic drift: random drift. The founder effect (founder populations) and bottlenecks (for some reason, pop size decreases dramatically, random allele frequencies might have more dominance)
- Nonrandom mating: when individuals choose their mates based upon their particular traits. Inbreeding (mating with family members) and sexual selection (when females only mate with certain males)
Genetic/ Hardy-Weinberg Equilibrium
When the allele frequencies remain constant from generation to generation. There is no evolution at genetic equilibrium.
What factors could make there not be genetic/hardy weinberg equilibrium?
- Natural Selection
- Mutations
- Gene Flow: movement of individuals between populations
- Genetic drift: random drift. The founder effect (founder populations) and bottlenecks (for some reason, pop size decreases dramatically, random allele frequencies might have more dominance)
- Nonrandom mating: when individuals choose their mates based upon their particular traits. Inbreeding (mating with family members) and sexual selection (when females only mate with certain males)
HW equilibrium equations and variables
p (dominant) and q (recessive) are allele values for each allele. Frequencies of homozygotes are psquared and qsquared. Frequency of heterozygotes is 2pq.
p+q=1 (all allele sum to 100%)
psquared + 2pq + qsquared = 1 (all ppl sum up to 100%)
Allopatric Speciation
Geographic barrier - reproductive isolation - differential evolution - reproductive barriers - new species
Sympatric speciation
The formation of a new species without the presence of geographic barriers.
- Balanced polymorphism, like in different colored insects who can only mate with other same colored insects bc they’d be eaten on a different substrate.
- Polyploidy. Polyploid individuals are unable to mate with other individuals because their gametes will have too many chromosomes. This is speciation in one generation
- Hybridization. Two species mate and form a hybrid zone, which may eventually diverge from both parent species
Adaptive Radiation
Occurs when a bunch of different species evolve relatively quickly from the same ancestral species. Happens when the original species is introduced into an area where there are lots of options for colonization. Ex: marsupials, galapagos finches
Prezygotic isolating mechanisms
Mechanisms that prevent fertalization in order to maintain reproductive isolation of a species
- Habitat isolation
- Temporal isolation: mate/flower @ diff times
- Behavioral Isolation: one species does not recognize the other as an option
- Mechanical isolation: physically doesn’t work
- Gametic isolation: male gametes don’t survive in the environment of the female gametes
Postzygotic isolating mechanisms
Mechanisms that prevent the formation of fertile progeny.
- Hybrid inviability: zygotes die
- Hybrid Sterility: like mules
- Hybrid breakdown: hybrids produce offspring that are messed up
4 Patterns of evolution
Divergent evolution, convergent evolution, parallel evolution, Coevolution
Divergent evolution
Two or more species that originated from the same ancestor and became species through allopatric, sumpatric speciation or adaptive radiation.
Convergent evolution
When species have analogous structures because they live in similar environments, not because they have a recent common ancestor. (The two species converged).
Parallel evolution
Two related species/lineages that make similar evolutionary changes after their divergence from a common ancestor.
