Evolution Flashcards
evolution
change in allelic frequencies in population
mostly takes place over hundreds, thousands, or millions of years
methods of dating Earth:
- studying undisturbed sedimentary rock layers and fossils within can reveal relative age
- absolute age can be accurately mesured by radiometric dating (decay of radioactive isotopes/halflifes)
- if not enough rock source, scientists use paleomagnetic dating (Earth’s magnetic poles shift and sometimes reverse and are recorded in rock layers)
- other methods include change in sea levels, molecular clocks, measurements of continental drift
history of Earth
- Earth has radically changed since forming 4.5 billion years ago
- continents shifted, climate through extreme cooling/warming, oceans risen and lowered repeatedly, volcanic activity brought major change and killed off species, meteorites killed dinosaurs and gave mammals chance to expand around globe
- 5 major extinctions have occured
- 4 billion years ago, non free oxygen: cyanobacteria (oxygen-generation organisms that form rock like structures, stromatolites) provided free oxygen for oceans + atmosphere
- high oxygen killed most anaerobic prokaryotes (oxygen is toxic) but also caused rapid diversification of life on land and in seas
- short period Cambrian explosion (535-525 mil years ago) characterized by sudden appearance of many present-day animal phyla
1. Fossil Record
6 pieces of evidence for evolution
- existence of species that may have gone extinct or evolved
- radiometric dating and half-life measures age of fossils
- prokaryotes first organisms to develop = oldest fossils
- paleontologists discovered transitional forms that link older fossils to modern species
- indicates that organisms living today is tiny fraction of every organism that lived: most life that existed on Earth went extinct
2. Comparative Anatomy
6 pieces of evidence for evolution
study of different structures help understand evolution of anatomical structures and evolutionary relationships
homologous structures
homologous structures have common origin and reflect common ancestry
wing of bat, lateral fin of whale, human arm all have same internal bone structure even if function varies
analogous structures
- bat wings and fly wings have same function, but very different
- similarity is superficial and reflects adaptation to similar environments, not descent from recent common ancestor
vestigial structures
structures with no apparent function, a residual from past ancestor
evidence that structures have evolved
e.g. appendix is a vestige of a structure needed when human ancestors ate a different diet
3. Comparative Biochemistry
6 pieces of evidence for evolution
- organisms with common ancestor will have common biochemical pathways
- more closely related = more similar biochemistry
e.g. medicine can be tested on mice and etrapolate the results to humans
4. Comparative Embryology
6 pieces of evidence for evolution
closely related organisms have similar stages in embryonic development
e.g. all vertebrate embryos go through stage with gill pouches on sides of throats - will deveop into gills in fishs, will develop into eustachian tubes in mammals
5. Molecular Biology
6 pieces of evidence for evolution
- because all aerobic organisms contain cells that carry out aerobic cell respiration, they all contain polypeptide cytochrome c
- comparison of amino acid sequence of cytochrome c in different organisms shows which organisms more closely related
- cytochrome c in human cells almost identical to chimpanzee and gorilla, but different from pig
6. Biogeography
6 pieces of evidence for evolution
- theory of plate tectonics (continents/oceans rest on giant plates of crust that floats on hot mantle) →convection currents in mantle causes continental drift
- plate movement over millions of years changed flora and fauna of Earth
- continental drift changed distributions of life on Earth
- e.g. marsupials only on Australia while other continents home to eutherians (true placental mammals), marsupials originated in Asia and reached Australia from South America and Antarctica while continents were joined, Australia set afloat like raft and carried marsupials and eutherians, marsupials filled every available niche in Australia while true placental mammals went extinct
historical context for evolutionary theory
- Aristotle had theory of Scala Natura: all life-forms can be arranged on ladder of increasing complexity, each with its own rung, species permanent and do not evolve, humans at pinnacle of ladder of increasing complexity
- Carolus Linnaeus/Carl von Linné (1707-1778) specialized in taxonomy (branch of biology for naming and classifying forms of life), believed that scientists should study life + classification system would reveal divine plan, developed binomial nomenclature (genus + species name)
- Georges Cuvier studied fossils and realized each stratum of earth characterized by different fossils, advocated catastrophism (series of events in past occured suddenly and caused by mechanisms different from present, events responsible for changes in organisms on Earth and strong opponent of evolution), influenced Darwin’s theory
- James Hutton (influential geologist) published theory of gradualism (1795), earth was molded and not by sudden events (effects of wind, weather, flow of wateer formed geologic features on earth), theory important because based on idea that earth had long history and change is normal course of events
- Charles Lyell (leading geologist in Darwin era) stated geological change results from slow, continuous actions, believed Earth much older than 6000 years, his work Principles of Geology had influence on Darwin
- Lamarck (contemporary of Darwin) published theory of evolution in 1809 (year Darwin was born) and had idea that inheritance of acquired characteristics + use and disues, stated individual organisms change in response to environment: giraffe has long neck because they stretched neck to reach leaves on tall acacia tree
- Alfred Russel Wallace (naturalist/author) published essay about natural selection similar to Darwin’s (not published yet), credited for theory along with Darwin
- Charles Darwin (naturalist/author, left England aboard HMS Beagle at 22 to visit Galapagos Islands, South America, Africa, Australia) worked out theory of natural selection or descent with modification as mechanism for evolution (1840s), eventually published “On the Origin of the Species” (1859)
Darwin’s Theory: Natural Selection
- major mechanism of evolution: acts on phenotypic variation in populations
- populations tend to grow exponentially, overpopulate, exceed resources
- overpopulation results in competition
- in any population, there is variation and unequal ability of individuals to survive + reproduce
- only best-fit individuals survive to pass on traits to offspring
- evolution occurs as advantageous traits accumulate in population (individual doesn’t change because of pressure in environment, but allelles become more frequent in population)
giraffe + long neck
- according to Darwin: ancestral giraffes were short-necked animals, although neck length varied
- as population of animals competing increased, taller individuals had better chance of surviving than those with shorter necks
- eventually, proportion of giraffes with longer necks increased until only long-necked giraffes existed
insects + resistance to pesticides
- insects do not become resistance, some insects naturally resistant to insecticide
- when environment sprayed, resistant insects have selective advantage
- all insects not resistant die, and remaining resistant ones breed quickly with no competition
- directional selection
1. Stabilizing Selection
5 types of selection
- eliminates extremes, favouring more common intermediate forms
- mutant forms weeded out
aka purifying selection
e.g. human babies weigh 6-8 pounds as larger or smaller results in greater infant mortality, Swiss starlings lay up to 5 has more surviving offspring vs. more or less eggs
2. Disruptive/Diversifying Selection
5 types of selection
- increases extreme types in population at expense of intermediate forms
- results in balanced polymorphism (1 population divided into 2 distinct types, may result in formation of 2 new species over time)
e.g. in environment with very light/dark rocks, very light/dark mice will increase while intermediate mice will die
3. Directional Selection
5 types of selection
- changing environmental conditions
- 1 phenotype replaces another in the gene pool
- can produce rapid shifts in allelic frequencies
e.g. industrial melanism in peppered moths, moths were light in 1845 in England but smog and smoke soon made plants and rocks dark, all moths dark by 1900
4. Sexual Selection
5 types of selection
- based on variation in secondary sexual characteristics to compete for mates
- difference in appearance between males and females known as sexual dimorphism (female birds blend in with environment while males are bright to compete for attention)
e.g. evolution of horns, antlers, large stature, strength: male elephant seals fight for supremacy of harem w/ 50 females, baboons have long canines, colourful birds
5. Artificial Selection
5 types of selection
humans breed organisms by seeking desired traits as breeding stock
e.g. racehorses, laying hens, types of vegetables
preserving variation in population
- variation necessary for population to evolve as environment changes
- even if it seems like natural selection will reduce genetic variation by removing unfavourable genotypes, 8 main mechanisms to preserve variation
1. Balanced Polymorphism
preserving variation in population
presence of 2+ phenotypically distinct forms of trait in a population
e.g. shells of a genus of land snail exhibits wide range of colors + patterns: banded snails living on dark + mottled ground less visible than unbanded ones, unbaned snails have selective advantage in areas where background is uniform
2. Geographic Variation
preserving variation in population
- 2 different rabbit variations exist in different regions of NA, graded variation in phenotype of organism known as a cline
- rabbit variation due to differences in northern + southern environments = north-south cline
3. Sexual Reproduction
preserving variation in population
- variation due to shuffling + recombination of alleles during meiosis/fertilization
- independent assortment of chromosomes in metphase I results in recombination of unlinked genes
- crossing-over is exchance of genetic material of homologous chromosomes in meiosis I
- random fertilization of ovum by sperm results in variety among offspring
4. Outbreeding
preserving variation in population
- mating of organisms within a species that are not closely related
- maintains variation in species and strong gene pool (inbreeding weakens gene pool because deterimental recessive traits appear in homozygous recessive individuals)
e.g. mechanisms to promote outbreeding: lion chasing away young maturing males
5. Diploidy
preserving variation in population
2n condition maintains + hides huge pool of alleles that are harmful in the present but may be advantageous when conditions change
6. Heterozygote Advantage
preserving variation in population
- preserves multiple alleles in population
- hybrid individuals sometimes better adapted than homozygotes
e.g. west africans hybrids (Ss) have normal hemoglobin and is resistant to sickle cell disease and malaria
7. Frequency-Dependent Selection
preserving variation in population
- decrease frequency of more common phenotype and increase less common
aka minority advantage
e.g. in predator-prey relationships, predators develop search image to make them hunt more effectively, rare individuals will have advantage and will become more common until they are selected against
8. Evolutionary Neutral Traits
preserving variation in population
traits with no selective advantage
e.g. blood types
genetic drift
causes of evolution of a population
change in gene pool due to chance
flucutation in frequency of alleles from generation to another
unpredictable and tends to limit diversity
bottleneck effect
- natural disasters reduce population unselectively, loss of genetic variation
- resulting population smaller and not representative of original
e.g. norther elephant seal almost hunted to extinction, government put under protection, and population increased from original group with little genetic variation
the founder effect
small population breaks away from larger to colonize new area
e.g. colonists from small group of settlers had 1+ settlers with gene for polydactyly (extra finger/toes), population now has high incidence of polydactyly
gene flow
causes of evolution of a population
movement of alleles into/out of population, increases diversity
from migration of fertile individuals between populations
e.g. pollen from a valley carried to another valley by wind
mutations
causes of evolution of a population
- changes in genetic material
- raw material for evolutionary change
- increase diversity
- single point of mutation can introduce new allele into population
nonrandom mating
causes of evolution of a population
selection of mate serves to eliminate less-fit individuals
e.g. snow geese exist in 2 phenotypically distinct forms: white + blue (blue tends to mate with blue and white tends to mate with white), if blue becomes more attractive, both blue + white geese will mate with blue geese, population would evolve quickly, favoring blue geese
natural selection
causes of evolution of a population
individuals better adapted exhibit better reproductive success
Hardy-Weinberg Equilibrium - Characteristics of Stable Population
- Hardy + Weinberg described characteristics of stable, nonevoling population: one where allelic frequencies do not change
- if population is stable:
1. population must be very large (small change in gene pool diluted by sheer number of individuals, no change in frequency of alleles will occur)
2. population must be isolated from other populations (no migration of organisms into/out)
3. must be no mutations in population
4. mating must be random
5. no natural selection
Hardy-Weinberg Equation
- used to calculate frequencies of alleles in a population
- p = dominant allele
- q = recessive allele
- equation: p^2 + 2pq + q^2 = 1 or p + q = 1
speciation and reproductive isolation
- species = population whose members can interbreed in nature and produce viable, fertile offspring
- species defined in terms of reproductive isolation (one group of genes becomes isolated from another to begin separate evolutionary history)
- once gene seperated, 2 isolated populations begin to diverge genetically under pressure of different selective forces/environments, 2 populations eventually can become so different interbreeding would not naturally occur (speciation)
- anything that fragments population and isolates small groups of individuals may cause speciation
allopatric speciation
caused by geographic isolation
e.g. mountain ranges, canyons, rivers, lakes, glaciers, altitude, longitude
sympatric speciation
without geographic isolation:
polyploidy: condition where cell has >2 complete sets of chromosomes
habitat isolation: 2 organisms live in same area but encounter each other rarely
behavioral isolation: male fireflies signal to females of their kind by blinking lights on tale in pattern, females respond only to characteristics of own species, flashing back to attract males, if female doesn’t respond with correct pattern, no mating occurs (isolated)
temporal isolation: flowering plant colonizes region warm vs. cool: flower in warmer regions become sexually mature sooner than flowers in colder area (2 populations)
reproductive isolation: closely related species unable to mate: differences in structure of genitalia, difference in flower shape, anything to prevent mating (prezygotic barriers), things that prevent production of fertile offspring after mating has occured (postzygotic barriers)
5 patterns of evolution
divergent, convergent, parallel, coevolution, adaptation radiation
divergent evolution
patterns of evolution
population becomes isolated from rest of species, becomes exposed to new selective pressures, evolves into new species
convergent evolution
patterns of evolution
unrelated species occupy same environment, subject to similar selective pressures, show similar adaptations
whale and fish similar but whale came from mammals
parallel evolution
patterns of evolution
2 related species that made similar evolutionary adaptations after divergence from common ancestor
tasmanian wolf (marsupial) vs. gray wolf
coevolution
patterns of evolution
reciprocal evolutionary set of adaptations of 2 interacting species
predator-prey relationships
adaptive radiation
patterns of evolution
emergence of numerous species from common ancestor introduced into environment, each newly emerging form specializes to fill an ecological niche
14 species of Darwin’s finches diverged from single ancestral species: 6 ground finches, 6 tree finches, 1 warbler finch, 1 bud eater
gradualism
modern theory of evolution
- organisms descend from common ancestor gradually in linear/branching method
- big changes from accumulation of small changes
- fossil record at odds with theory, rarely found transitional forms or missing links
punctuated equillibrium
modern theory of evolution
- favored theory of evolution today by Stephen J. Gould + Niles Eldridge
- proposes new species appear suddenly after long periods of stasis
- new species changes most as it buds from parent species, then changes little for rest of existence
- sudden appearance of new species explained by allopatric model speciation
- new species arises in different place and expands range, outcompeting, replacing ancestral species
evo-devo
- evolutionary development biology
- major changes in body form/function come about when some genes regulate other genes
- DNA sequence that codes for structure identical in different species, but genes might be upregulated/downregulated by other genes for different outcomes
humans and chimps so different when DNA almost identical
homeotic genes
- master regulatory genes that control spatial organization of body parts
- determines where features go on insect/flower
e.g. Hox gene provides positional information in developing embryos
heterochrony
evolutionary change in rate or timing of development of body parts
infant human/chimp skull very similar but human skull seems to stop before chimp changes happen, genetic code for morphology of skull might be identical but something signals human skull genes to stop developing sooner
origin of life
- ancient atmosphere made of CH4, NH3, CO, CO2, N2, H20 but lacked free O2
- intense lighting and UV radiation that penetrated primitive atmosphere providing energy for chemical reactions
- A.I Oparin + J.B.S Haldane (1920s) hypothesized seperately that under conditions, organic molecules can form
- organic molecules could form and remain without corrosively reactive molecular oxygen to react with
- Stanley Miller + Harold Urey (1950s) tested Oparin-Haldane hypothesis and proved that almost energy source can convert molecules in early atmosphere into variety of organic molecules (e.g. amino acids), used electricity and UV lights to mimic environment
- Sidney Fox (recent) began with organic molecules, and able to produce membrane-bound, cell-like structures that could last for several horus (proteinoid microspheres)
heterotroph hypothesis + theory of endosymbiosis
- first cells anaerobic heterotrophic prokaryote, absorbed organic molecules from surrounding primordial soup for nutrients, evolved around 3.5 billion years ago
- eukaryotes didn’t evolve until 2 billion years after evolution of prokaryotes, arose from endosymbiosis (theory by Lynn Margulis: mitochondria + chloroplasts once free-living prokaryotes and took up residence inside larger prokaryotic cells)
- proof that mitochondria + chloroplasts endosymbionts: have own DNA, DNA more like prokaryotic DNA than eukaryotic DNA (not wrapped with histones), organelles have double membranes
RNA world
- concept hypothesizes that 4 billion years ago, first genetic substance on Earth not DNA molecule but small, single-stranded RNA molecule
- ribozyme (RNA type) can catalyze reactions like enzme, also transmit info like DNA
- functions of ribozyme: functions as enzyme to catalyze reactions, splices RNA by itself without need for proteins, removes own introns during RNA processing, joins amino acids together to form polypeptide during translation in ribosomes
- hypothesis gone from speculation to prevailing idea in past 50 years
- ribozyme is exception to idea that all biological catalysts are proteins, RNA is not protein
exaptation
- not every trait results because it is adaptive (natural selection)
- traits evolved by natural selection but then co-opted for another purpose
feathers originally arisen as adaptations in context of selection for insulation, but later co-opted for flight: adapatation for insulation and exaptation for flight
half-life
- used for most common way to determine absolute age of fossil (radiometric dating)
- half-life = natural decay of radioisotopes
- time required for half of nucleus of radioactive sample to decay to its products
- after 1 half-life passed, half of original materical decayed into atoms of new element, other half intact
- can be a fraction of second or a billion years
- not affected by temperature, pressure, or any other environmental conditions
- fossils have isotopes of elements that accumulated in organism when alive (mostly stable carbon isotope C-12 as well as small amount of radioactive C-14, when organism dies, stops accumulating carbon and amount of C-12 in tissues remain same but C-14 decays slowly into another element (N-14) – determine age by measuring ratio of C-14 to C-12
- over 75 000 years contain too little C-14 to be detected
dating over 75 000 years
- dated indirectly if fossil embedded in volcanic rock
- cooling lava might absorb + trap radioisotopes from surrounding environment
- if fossil sandwiched between 2 layers of volcanic rock and if we can date two layers by half-life, age range is known
