Evolution Flashcards
Approximately when did the planet form?
~4.6 bya
What were the initial conditions of the planet?
Much hotter
No oxygen
Lots of UV, lightning, volcanoes and meteorites
No life
What is the 4 step hypothesis of how life evolved?
- Organic monomers were synthesized abiotically
- polymers formed abiotically
- ex. proteins, nucleic acids - molecules were packaged into protocells
- molecules formed that made inheritance possible
Where would the energy have come from to abiotically synthesize organic molecules when life began to form?
UV and lightning
How could some organic molecules have arrived on Earth?
On meteorites
Which element, that was abundant on Earth pre-life, has been recently found to catalyze metabolic reactions?
Ferrous iron
Define protocells
Droplets of fluid with membranes that maintained internal chemistry different from their surroundings
T or F: protocells could form abiotically and divide and grow?
True
What is an example of a molecule that made inheritance possible?
Self-replicating RNA molecules
What was likely the first hereditary material? Why?
RNA because it is simpler than DNA and easier to form abiotically
What enzymes formed when RNA was formed?
Ribozymes (RNA enzymes)
Overtime, what became the universal genetic material instead of RNA? Why?
DNA because it is more stable and can be more accurately copied
What is the general timeline for evolution of life on Earth?
- 3.5 bya: Prokaryotes (stromatolites)
- ~3.9 bya: Single cells may have evolved earlier
- ~2.7 bya: Photosynthetic prokaryotes
- 2.1 bya: single-celled eukaryotes
- 1.2 bya: multicellular eukaryotes
- 1 bya: prokaryotes colonized land
- ~500 mya: larger life forms colonized land
How long ago did prokaryotes evolve? What is the evidence that supports this?
at least 3.5 bya
Earliest evidence is fossilized stromatolites
What are stromatolites?
Layered rocks formed by prokaryotes that are likely the first form of life to evolve
How long ago may single cells have evolved? Why is there less evidence for this?
~3.9 bya
Less evidence because they’re simpler than prokaryotes and may not have fossilized well
How long ago did photosynthetic prokaryotes evolve?
~2.7 bya
What atmospheric change did the evolution of photosynthetic prokaryotes cause?
An increase in atmospheric oxygen
How long ago did single-celled eukaryotes evolve?
2.1 bya
What atmospheric change did the evolution of single-celled eukaryotes cause?
A more rapid increase in oxygen levels
How long ago did multicellular eukaryotes evolve?
At least 1.2 bya
How long ago did prokaryotes colonize land?
Over 1 bya
How long ago did larger life forms colonize land?
~500 mya
How did Darwin define evolution?
As descent with modification
What is the current definition of evolution?
A change in the genetic composition of a population from generation to generation
Define Darwinism
the hypothesis of natural selection proposed by Darwin
T or F: Darwin’s hypothesis of natural selection is now an accepted theory
True
What was the accepted paradigm during Darwin’s time for species?
That species had a fixed form (ie, they do not evolve over time)
What field of science did Georges Cuvier develop?
Palaeontology (study of fossils)
What were Cuvier’s 2 biggest discoveries?
He found that the older the layer of rock, the greater the differences between fossils and current life forms
That species appeared and disappeared in different layers of rock
What was Cuvier’s proposal for why species appeared and disappeared in rock layers?
This was due to local catastrophes rather than that species change over time (he rejected evolution)
What field of science did Charles Lyell study?
Geology
What did Lyell propose?
That the mechanisms of change are constant over time and that geological processes always operate at the same rate
over time, small changes can add up to a substantial change (ex. a river carving a canyon)
Who was Lyell’s work based on?
James Hutton, another geologist
What 2 things did Darwin reason from Lyell and Hutton’s work?
- the earth was much older than a few thousand years (as was previously thought)
- a slow and similar process (to geological processes) might change life forms
What did Jean-Baptiste Lamarck study?
Compared living species with fossil forms
What 2 things did Lamarck find in his studies?
He found several lines of descent where fossils led to living species
Organisms’ environmental suitability can be explained by gradual evolutionary change
What was Lamarck’s proposed hypothesis of evolution?
Body parts that were used became larger and stronger and those unused deteriorated
And that organisms could pass on these modifications to their offspring
What is Lamarckism?
Organisms can pass on their individual modifications to their offspring
What is wrong with Lamarck’s conclusions?
Frequently used body parts will not become larger or stronger during an individual’s life time
and the hypothesis of evolution is wrong at the organismal level
What did Charles Darwin do on his voyage around South America on the Beagle?
Observed and collected thousands of organisms
Noted that organisms were always well suited to their environment
What did Darwin discover about the Andes? What conclusion did this lead him to draw?
He found fossils of oceanic organisms up in the Andes and concluded that because earthquakes can lift rocks, the fossil containing rocks must have been at sea level and were lifted by earthquakes over time
This meant that the Earth had to be older than a few thousand years
What did Darwin notice about the species on the Galapagos Islands? What did this lead him to conclude?
They were unique but still resembled those on the mainland
He hypothesized that the islands were colonized by mainland organisms that diversified and gave rise to new species
What is an example of the differences Darwin noticed between finches of different islands of the Galapagos?
Beaks of finches were adapted for food sources on each island
ex. cactus-eater vs insect-eater vs seed-eater all have different beaks
Define adaptation
Inherited characteristics of organisms that enhance their survival and reproduction in specific environments
What did Darwin hypothesize as a cause of speciation?
Populations in a new area can accumulate new adaptations
What do adaptations arise from?
natural selection
Define natural selection
A process in which individuals in a population that have certain inherited traits will survive and reproduce at greater rates than individuals without the traits
What was the name of the other naturalist who was also studying evolution at the same time as Darwin?
Alfred Russel Wallace
What year was On the Origins of Species by Darwin published?
1859
What were Darwin’s 3 main findings?
- evolution = descent with modification
- All organisms have descended from one ancestor
- Organisms changed and adapted to specific environments which led to the diversity of life
What are Darwin’s 2 observations?
- Members in the population often have variable inherited traits
- All species can produce more offspring than the environment can support and many will not survive
What are Darwin’s 2 inferences?
- Individuals that have better fit traits will tend to have higher survivorship and more offspring
- unequal survivorship and reproduction rates will cause population to accumulate favourable traits
Define Neo-Darwinism/new Darwinism
The comprehensive theory of evolution including genetics
What happened in the 1930s in regards to genetic heredity?
Population geneticists started studying genetic variation and quantitative characters
Define macroevolution and give examples
Broad pattern of evolution above the species level
ie, sweeping changes in life on Earth above the species level
ex. mass extinctions, evolution of flight, evolution of seeds
What are 4 types of evidence for macroevolution?
- direct observation
- homology
- fossil record
- biogeography
Describe direct observation, give an example
Biologists have documented evolutionary changes in thousands of scientific studies
ex. beak length in soapberry bugs changed when the plant they fed on became rare and they started to feed on an invasive species
describe homology and give an example
similar characteristics as a result of common ancestry
ex. bones in forelimbs of mammals are homologous but modified for different modes of travel
define homologous structures
variations on a structural theme that was present in a common ancestor (anatomical or molecular)
describe embryology and give an example
early stages of development in different animals show additional homologies
ex. the four chordate characteristics
Describe vestigial structures and give an example
Remnants of homologous structures that served a function in the organism’s ancestors
ex. arrector pili muscles in humans - in other mammals the muscles cause fur to stand up as insulation or to make the animal seem larger when threatened
describe molecular homologies
All life shares some genetic characteristics from a distant common ancestor
What is an example of something that is found in all life forms?
nucleic acids
T or F: humans share genes with other organisms including prokaryotes
true
Will more closely related organisms have fewer or more homologies? why?
More, due to a more recent common ancestor
Define convergent evolution, give an example
When natural selection causes the evolution of similar features in different lineages
ex. gliding in rodents in different parts of the world (sugar glider vs flying squirrel) - similar niches with similar selectional pressures
Describe the fossil record
Shows evolutionary changes that have occurred and reveals common ancestors that are now extinct to help complete the tree of life
What does the fossil record show when species appear and disappear?
Succession of life forms
What were the first life forms?
Prokaryotes
Define biogeography
The study of the distribution of species on Earth
What is Pangea?
The single landmass that used to exist on earth and broke apart ~200 mya
Define endemic species
Species that are found only in one place (often islands)
They are similar to the mainland species because they were colonized from the mainland but have adapted to their new environment and became a new species
T or F: closely related endemic species tend to be in the same regions
True, example is marsupials in Australia
T or F: natural selection works on individuals and therefore individuals can evolve
FALSE. Natural selections works on individuals, but individuals CANNOT evolve
What is the smallest unit of evolution?
Population
Define population
members of a species in the same geographic area at the same time that interbreed and produce viable offspring
Evolution works on ___ characteristics which must be ____
heritable; variable
T or F: changes in the environment can change which adaptations are selected for
True
Initially, black peppered moths were rare and lighter coloured moths were more common because they were better camouflaged. When the industrial revolution blackened the trunks of trees, what happened to the moths?
The darker moths became more camouflaged against the blackened trees and so they became more common than the light coloured moths that now stood out and were more heavily predated by birds
Define microevolution
Changes over time in the genetic composition of a population over many generations
Define allele frequency
Proportion of the population that has the alternative version of a gene
What are the 3 main causes of microevolution?
- natural selection
- genetic drift
- gene flow
Which of the 3 main causes of microevolution reliably increases the frequency of favourable alleles?
natural selection
Define genetic drift
a process where CHANCE events can cause changes in allele frequency
Is genetic drift always adaptive?
No because the allele change may not be the best allele since genetic drift occurs randomly
What size of a population does genetic drift have a larger impact on?
Small populations
What are the two main types of genetic drift?
- bottleneck effect
2. founder effect
Define bottleneck effect
1/2 types of genetic drift
Occurs when a random change (such as a natural disaster) wipes out most of the population and…
the surviving population has different genetic frequency than the original population after the event
Define founder effect
1/2 types of genetic drift
Occurs when few individuals become isolated from a larger population (ex. when a few organisms are blown/float to a new island) and…
the new population will have a different genetic frequency than the original population
Define gene flow
the transfer of alleles into or out of a population due to the movements of fertile individuals or their gametes (ex. pollen)
What is an example of gene flow?
The spread of insecticide resistance in mosquitoes
- the resistance alleles were a result of mutations
- spread to other populations through gene flow
- frequencies increased due to natural selection
Is gene flow adaptive?
Not necessarily because the outcome can be random
Define natural selection
the process in which individuals that have certain traits tend to survive and produce more offspring because of those traits
Is natural selection adaptive?
yes, the outcome is not random
How does natural selection affect allele frequencies?
It increases allele frequencies for traits that enhance survival and reproduction in the environment
What three ways does natural selection alter the frequency distribution of traits?
- directional selection
- disruptive selection
- stabilizing selection
Describe directional selection
1/3 ways natural selection alters frequency distribution of traits
Favours one extreme of phenotypes and
occurs when conditions favour individuals exhibiting an extreme value in the phenotype range
Which way does the population frequency curve shift when directional selection occurs?
to the left or to the right (one of the extremes)
When is directional selection common?
When the environment changes or members of a population migrate to a different habitat
Describe disruptive selection
1/3 ways natural selection alters frequency distribution of traits
When conditions favour individuals at both extremes of the phenotype range but not those with intermediate phenotypes
What is an example of disruptive selection?
birds with small beaks and birds with big beaks are favoured
Birds with moderately sized beaks are not as good at feeding on soft or hard seeds and are therefore less favoured
Describe stabilizing selection
1/3 ways natural selection alters frequency distribution of traits
When conditions favour the intermediate phenotypes but not the extremes
Reduces variation
Which of the 3 ways natural selection alters frequency distribution of traits reduces variation?
Stabilizing selection
What is an example of stabilizing selection
Birth weights of most human babies is 3-4 kg, and those outside that range have higher rates of mortality
Which way does the population frequency curve shift when disruptive selection occurs?
To both the left and right (the extremes)
Which way does the population frequency curve shift when stabilizing selection occurs?
Shifts inward and upward (gets taller and narrower)
How can genetic variation be measured?
As gene variability (% of heterozygous loci –> different alleles) or
nucleotide variability (% sequence differences)
What are 3 causes of genetic variation?
- mutations (gene, chromosomes, or genome)
- recombination
- mostly, sexual reproduction
How does sexual reproduction cause genetic variation?
It shuffles around existing alleles into new combinations
Do most populations show considerable or minimal genetic variation?
considerable
T or F: genetic variation has no effect on the health of a population
FALSE.
Populations need a certain amount of variation to be healthy
Are there genetic variations that have neutral results/cause no selective advantages?
Yes
ex. fingerprints
Define Darwinian fitness
The relative contribution of an individual to the gene pool of the next generation
What is an example of Darwinian fitness?
Ghengis Khan’s lineage is very fit as 1/200 men alive today are his descendants
Define relative fitness
chances of survival and fertility of a genotype
Does selection act on genotypes or phenotypes?
Phenotypes
What can differential reproductive success lead to?
change in populations
Define the biological species concept
A group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring
Define reproductive isolation
Existence of biological factors (barriers) that impede members of two different species from interbreeding and producing viable, fertile offspring
What are two purposes of reproductive isolation?
- maintain integrity of closely related species
2. formation of new species hinges on this
What are prezygotic barriers?
Ways to impede matings or prevent fertilization
What are 5 prezygotic barriers?
- habitat isolation
- temporal isolation
- behavioural isolation
- mechanical isolation
- gametic isolation
Describe habitat isolation
1/5 prezygotic barriers
Species in aquatic and terrestrial environments would not interbreed even if they’re in the same area
Describe temporal isolation
1/5 prezygotic barriers
Species have different breeding times (ex. times of day, seasons, years)
Describe behavioural isolation
1/5 prezygotic barriers
Species have different courtship rituals
Describe mechanical isolation
1/5 prezygotic barriers
Species have morphological differences to prevent completion of mating
Describe gametic isolation
1/5 prezygotic barriers
Sperm of one species may not survive the reproductive tract of female of another species
Or
biochemical mechanisms can prevent the sperm from fertilizing the egg
What are postzygotic barriers?
If fertilization occurs, these are ways to maintain reproductive isolation
What are 3 postzygotic barriers?
- reduced hybrid viability
- reduced hybrid fertility
- hybrid breakdown
Describe reduced hybrid viability
Hybrids fail to develop or may not survive
Describe reduced hybrid fertility (give an example)
hybrids are not fertile
ex. mules (cross between donkey and horse are sterile)
Describe hybrid breakdown
First generation is fertile but later generations are not or are weak
Define speciation
A process by which a group of individuals which can breed together splits into two or more groups that can no longer interbreed between them
OR
One species splits into two or more species
When can speciation occur?
When a group is reproductively separated from parent species and the group changes enough to form a new species
What 2 ways can speciation occur?
- allopatric speciation
2. sympatric speciation
Describe allopatric speciation
When gene flow is interrupted because population has been geographically isolated into subpopulations
What causes allopatric speciation?
A change in habitat
ex. a lake drying, river changing course, formation of canyons
What are 4 reasons allopatric speciation cause an isolated subpopulation to become a new species?
The subpopulation will be genetically different from the parent population (FOUNDER EFFECT)
Genetic drift occurs and will have a profound effect cause the group will likely be small
different mutations can occur
natural selection may favour different traits in a new habitat
Define sympatric speciation
Speciation that occurs in populations that live in the same geographic area
Why is sympatric speciation less common than allopatric?
Because the species are still in the same geographic area so they can still interbreed
What are 3 examples of sympatric speciation?
- polyploid speciation in plants
- habitat differentiation
- sexual selection (may be triggered by colour)
How does habitat differentiation work as a form of sympatric speciation?
A subpopulation can exploit habitat or resources not used by the parent population
Define adaptive radiation
evolution of many new species from a common ancestor
How does adaptive radiation work?
New species can fill different ecological roles or niches
What 3 reasons could adaptive radiation occur?
- After mass extinctions when there are many vacant niches
- when ancestors have evolutionary innovations such as seeds or armoured body coverings
- when new island chains form (volcanism)
- ex. Hawaiian or Galapagos Islands
What are 4 reasons why natural selection cannot fashion perfect organisms?
- selection can only act on existing variations and ideal variations may not exist
- evolution is limited by historical constraints because it adapts EXISTING structures to new situations
- chance, natural selection and the environment all interact causing a moving target for natural selection
- adaptations are often compromises
How does the interaction between chance, natural selection and the environment effect evolution?
- chance can affect evolution:
- natural disasters don’t necessarily only affect the worst or best adapted individuals - environmental change can cause moving targets for natural selection –> one year one trait might be adaptive and the next year it’s not
In what way are adaptations often compromises? Give an example
traits can be advantageous in one way but disadvantage in another
ex. adaptations for speed can lead to fragility of limbs
