Processes of Evolution Flashcards
Evolution
the change in genetic composition and makeup of populations over time
Evolutionary theory
the understanding of the mechanisms of evolutionary change
Darwin’s 3 propositions of theory
- Species change over time
- Divergent species share a common ancestor, and species have diverged gradually through time (descent with modification).
- The mechanism that produces the change is natural selection: the differential survival and reproduction of individuals based on variation in their traits
5 processes of evolution
Mutation, gene flow, genetic flow, genetic drift, and nonrandom mating
Hardy Weinburg equation
p^2 + 2pq + q^2 = 1, where p^2 = frequency of homozygous dominant genotype, 2pq = frequency of heterozygous genotype, and q^2 = frequency of homozygous recessive genotype
Conditions met in the Hardy Weinburg equation
No mutation
No selection among genotypes
No gene flow
Population size is infinite
Mating is random
Natural selection can act on quantitative traits in 3 ways:
- Stabilizing selection
- Directional selection
- Disruptive selection
Stabilizing selection
preserves the average phenotype
Directional selection
favors individuals that vary in 1 direction from the mean
Disruptive selection
favors individuals that vary in both directions
Trade-offs
result in traits that are adaptive in one context but not another. Ex: rough-skinned newts make the neurotoxin tetrodotoxin (TTX), which paralyzes nerves and muscles.
4 eons
- Hadean eon - before life evolved
- Archean eon - early life
- Proterozoic eon - first eukaryotes. First 3 are known collectively as the Precambrian (4 billion years)
- Phanerozoic eon - diversification of eukaryotes.
Hadean eon
Earth’s forming: surface is cooling, ocean forms, meteorites, no oxygen, no life
Archean eon
atmosphere accumulates, less meteorites, still almost no oxygen, origin of life
Impact of weather conditions on Earth
During the Carboniferous and Permian periods, massive burial and decomposition of organic material transformed dead plants and animals into fossil fuels - occurred over millions of years ago. Burning these fossil fuels is releasing that stored carbon as CO2 - occurring over a few hundred years
By 2100, temps are expected to increase by 2-3 degrees C. The last temperatures were that high sea level was 24 meters high
Proterozoic eon
origin of photosynthesis, oxygen accumulates from the atmosphere, there’s eukaryotes and multicellular organisms
Phanerozoic eon
diversification of eukaryotes, mass extinctions
Why do some species go extinct
lack of resources, reproductive partners, no prey = no predators, predators outnumber prey
What’s the Cambrian explosion
It is the time when most of the major groups of animals first appear in the fossil record. Soft bodied multicellular organisms began to evolve
4 major environmental changes
- Ordovician period - marine organisms occurred and mass glaciers formed
- Devonian period: an extinction at the end of the Devonian resulted in loss of 75% of marine species
- Carboniferous period: large glaciers formed over high latitude, but great swamp forests of horsetails and tree ferns grew on the tropical continents
- Permian period: the continents merged to form the supercontinents Pangaea
- Cretaceous period: modern continents began to form. A continuous sea encircled the tropics. Earth was warm and humid
Other important events
- Triassic period: the surviving organisms inhabited a relatively empty world
Continents began to drift apart; sea levels rose and flooded the continents forming large shallow seas - Jurassic period: Pangaea divided into Laurasia, which drifted southward
First lizards and flying reptiles (pterosaurs) appeared; most large terrestrial animals were dinosaurs - Cretaceous period: modern continents began to form. A continuous sea encircled the tropics. Earth was warm and humid
- Paleogene period: Amphibians, snakes, lizards, birds, and mammals underwent extensive radiations
- Neogene period: continents began to take their current positions
