midterm1 Flashcards
selection acts on ____ *not ____
selection works ____ and mainly on ____________
selection acts on phenotypes *not genotypes
selection works fast and mainly on traits for mating postulates
there is tremendous diversity ____ species as well as ____ species
there is tremendous diversity within species as well as between species
Evolution by NS explains:
1. ____: NS promotes ___ by causing innumerable ____ _____ throughout the history of life
2. _____: NS promotes by ____ individuals with ____ that ____ them survive and reproduce in their environment
3. ____: NS promotes _____ by favoring the cumulative build up of _____ improvements in ______ design.
Evolution by NS explains:
1. diversity: NS promotes diversity by causing innumerable branching events throughout the history of life
2. Adaptation: NS promotes by favoring individuals with traits that help them survive and reproduce in their environment
3. complexity: NS promotes complexity by favoring the cumulative build up of small improvements in organismal design.
2 evolution hypotheses
1 special creation
2 descent with modification (evolution)
evolution definition
inherited change in a group of organisms over time (generations
vestigial traits example
brown kiwi with useless wings
transitional fossils
tikaalik that transitions between fish and land-dwelling
homology: possession by ___ or more species of a ____ (example: a morphological structure or a behavior) that is _____, with or without _____, from their common ancestor. Think _____?
homology: possession by two or more species of a trait (example: a morphological structure or a behavior) that is derived, with or without modification, from their common ancestor. Think common bones between humans, dolphin, etc.
all organisms have the virtually same ___ ____; helps explain at the ____ ____ how we can understand human diseases using other _____
all organisms have the virtually same genetic code; helps explain at the deepest levels how we can understand human diseases using other organisms
what is evidence of evolution?
direct observation (in natural populations)
NS is the ____, ______ survival and/or reproduction of individuals that differ in one or more _____
NS is the nonrandom, differential survival and/or reproduction of individuals that differ in one or more characteristics
NS can lead to evolution but doesn’t always do so why?
*other ways to create evolution
1 there are other ways to produce evolutionary change (genetic drift/bottleneck) or mutation or migration
evolution produces a ____-like pattern… humans did NOT evolve from ____ (but we share a ____ ____ with ___)… humans are NOT more ___ ____ than other primates
evolution produces a tree-like pattern… humans did NOT evolve from apes (but we share a common ancestor with apes)… humans are NOT more highly evolved than other primates
evolution by NS does not lead to ____; instead, is more like a ____ to ____ on what is already there
evolution by NS does not lead to perfection; instead, is more like a tinkerer to improve on what is already there
____ evolution by NS can to complexity. Think ____?
gradual evolution by NS can to complexity. Think blind cavefish
microevolution can lead to macroevolution
domestic breeds of domestic dogs although there is more variation between the breeds with size and color = micro
different species have little variation between breeds size and color like wolf vs fox = macro
Selection acts on the_____ of individuals but its consequences consist of _____ changes in _____
selection can take different forms or “____”
Selection acts on the phenotypes of individuals but its consequences consist of heritable changes in populations
selection can take different forms or “modes”
studies that have measured selection have revealed that selection in many natural populations is ____ enough to cause a ____ evolutionary change in a _____ period of time
studies that have measured selection have revealed that selection in many natural populations is strong enough to cause a substantial evolutionary change in a short period of time
Selection acts stronger on traits associated with _____ than on traits associated with _____
Selection acts stronger on traits associated with mating success than on traits associated with survival
Although _____ is common, organisms might not express the “____” trait because of various limitations or constraints
Although adaptation is common, organisms might not express the “perfect” trait because of various limitations or constraints
selection only occurs when individuals with certain traits produce _____ offspring than individuals with other traits
this means that selection requires:
1 ______
2 ___________, where some individuals produce ____ offspring BECAUSE of their particular traits
Moreover, for selection to produce evolution requires:
3 _____, where the ____ _____ individuals distinctive traits are passed on to their offspring
selection only occurs when individuals with certain traits produce more offspring than individuals with other traits
this means that selection requires:
1 variation
2 differential survival/reproduction, where some individuals produce more offspring BECAUSE of their particular traits
Moreover, for selection to produce evolution requires:
3 inheritance, where the selectively favored individuals distinctive traits are passed on to their offspring
if selection is weak, how big mean size of reproducing individual?
big and medium
OR
medium and small
if selection is strong, how big mean size of reproducing individual?
only big
or
only small
For evolution to occur, there must also be ______; thus if heritability = 0, the mean value of the parents will be the _________ for the offspring.
What is R=h^2*S
For evolution to occur, there must also be inheritance; thus if heritability = 0, the mean value of the parents will be the same value for the offspring.
The evolutionary response to selection R=h^2*S
4 postulates?
1 individuals within species are variable
2 variation among individuals can be inherited
3 all organisms face a struggle for existence because more offspring are born that can survive to reproduce
4 in such a situation, survival and reproduction are nonrandom
Darwin arrived at the first two postulates (_____ and _____) because of his observations of _____ species that had undergone _____ ____.
Darwin arrived at the first two postulates (variation and inheritance) because of his observations of domesticated species that had undergone artificial selection.
Darwin’s breakthrough (the ____ postulate) was to realize that “A struggle for existence is universal whenever more individuals are produced than can possibly survive.”
This insight was inspired by the cleric and scholar _____ _____.
Darwin’s breakthrough (the third postulate above) was to realize that “A struggle for existence is universal whenever more individuals are produced than can possibly survive.”
This insight was inspired by the cleric and scholar Thomas Malthus.
What is heritability?
Heritability (H) is the ratio of the total phenotype variation in a ‘quantitative’ trait that can be attributed to genetic variation among individuals in a population; broad-sense heritability
What issues complicate measuring heritability in the wild?
(1) Misidentified paternity (females may engage in extrapair sex)
(2) Conspecific nest parasitism (egg dumping)
(3) Shared environments (relatives share environments as well as genes)
(4) Maternal effects
What is the difference between narrow-sense heritability and broad-sense heritability?
‘Narrow-sense heritability’ is the ratio of the total phenotype variation in a trait that is due to additive genetic variation
broad-sense heritability is general heritability (ratio of total phenotype variation to total genetic variation in a trait)
finches + seeds
during drought, what 4 things changed.
outcome?
1 finches overall number decreased
2 number of seeds declined
3 characteristics of seeds also changed
4 large-beaked birds were favored
outcome: finch population evolved
Why don’t species always evolve in one direction?
the direction of selection fluctuates
phenotypic plasticity example
eating hard seeds may cause more keratin to be deposited on the beak. even when a trait shows plasticity, plasticity may still have a heritable basis and can be a target of selection
Individuals with different ____ typically vary in whether and how they respond to the _____
Individuals with different genotypes typically vary in whether and how they respond to the environment.
How does directional, stabilizing, and disruptive selection change during and after selection?
what do these explain?
directional selection: during, fitness increases linearly. after, phenotypes look like smaller bell curve shape as original
stabilizing selection: during, fitness is bell curve. after, phenotypes shape has selected for the middle ones, so deep drop off
disruptive selection: during, fitness is U shaped. After, phenotypes shape is flat
these explain how selection can assume different modes
stabilization usually leads to…
differentiation between tadpoles (omnivores and carnivores with different niches)
We can measure the trait values for a ____ of individuals and then estimate the ____ associated with different trait values.
The relationship between variation in ________ and variation in the _______ represents _____ on the trait.
We can measure the trait values for a sample of individuals and then estimate the fitness associated with different trait values.
The relationship between variation in relative fitness and variation in the trait values represents selection on the trait.
The regression between ______ values (z) and _____ (w) of those phenotypes is called the _____ _____
If this relationship is described by a straight line, __________________
This measure of the strength of selection is called the ____ _____ (Beta).
The regression between phenotypic values (z) and fitnesses (w) of those phenotypes is called the fitness function.
If this relationship is described by a straight line, the strength of selection is given by the slope, b, of the regression.
This measure of the strength of selection is called the selection gradient (Beta).
how strong is phenotypic selection in natural populations?
very strong, enough to cause substantial evolutionary change in 10-100 generations (very small in evo time)
Interestingly, the strength of selection is greater due to variation in ____ ____ than that due to variation in _____
Interestingly, the strength of selection is greater due to variation in mating success than that due to variation in survival.
What is an adaptation?
An adaptation is a characteristic (or a specific trait value) that increases the fitness of an individual compared to individuals that lack the trait (or that express a different trait value).
Why do organisms often not express the “perfect” trait (or trait value) for their particular circumstances?
1
2
3
4
1 selection can act on different levels
2 time lags may preclude adaptation –> evo is at least a generation behind any changes in the environment
3 genetic constraints may preclude adaptation: When the heterozygote has a higher fitness than either homozygote, the population evolves to an equilibrium at which all three genotypes are present. A proportion of the individuals must therefore have the deleterious homozygous genotypes.
This constraint arises because the heterozygotes cannot, under Mendelian inheritance, produce purely heterozygous offspring; i.e., they cannot “breed true.” think: sickle cell
Also, pleiotropy: where a single gene influences more than one trait. A mutation in a gene may produce a better version of one trait, while also producing worse versions of other traits whose development that gene influences.
4 selection itself may preclude the “perfect” adaptation: selection might be precluded from evolving toward an adaptive trait value because of a selective “valley.” Additionally, selection can only refine a trait that it actually ‘sees.” The best way of illustrating such a selective constraint is to consider the evo theory for why all living things senesce (age) and die
genetically engineered trees in forest that still end up dying because of diseases or natural disasters
The evolutionary theory of senescence
The selective effect of any allele _____ with the ___ at which that allele is _____ in the individual –> An allele affecting the phenotype at old age will have ____ effect on fitness, because the organism…?
Moreover, the organism will have..?
The theory we have just outlined is called the “____ ____” hypothesis like cancers, Huntington’s or old age
A slightly different hypothesis is the “____ _____” hypothesis
According to this hypothesis, a mutation that has two effects - early in life? but late in life? - can be favored by ____ (“live fast, die young”)
E.g., compare annual versus perennial plants
The selective effect of any allele decreases with the age at which that allele is expressed in the individual
An allele affecting the phenotype at old age will have little effect on fitness, because the organism will usually have died of something else by then (e.g., accidents, disease).
Moreover, the organism will have already reproduced and passed along the late-acting mutant allele to its offspring!
The theory we have just outlined is called the “mutation accumulation” hypothesis like cancers, Huntington’s or old age
A slightly different hypothesis is the “antagonistic pleiotropy” hypothesis
According to this hypothesis, a mutation that has two effects - increased fitness early in life but decreased fitness late in life - can be favored by selection (“live fast, die young”)
E.g., compare annual versus perennial plants
There are significant _____ in studying the origin of life: e.g., the _____ on the early Earth were dramatically ____ than they are today. Also, we know of only ___ instance in which ___ has arisen!
There are significant difficulties in studying the origin of life: e.g., the conditions on the early Earth were dramatically different than they are today. Also, we know of only one instance in which life has arisen!
Defining “___” is problematic. However, all ___ is subject to ____ ____
Defining “life” is problematic. However, all life is subject to natural selection
Life may have been based initially on ___. Cellular life likely arose > ____
Life may have been based initially on RNA. Cellular life likely arose > 4 bya!
Darwin first proposed the “___ ___” theory for the origin of life. This theory was demonstrated in the lab in the ____
Many scientists now believe life arose near _______
However, life may have arisen elsewhere (e.g., ____) and traveled to ____!
Darwin first proposed the “prebiotic soup” theory for the origin of life. This theory was demonstrated in the lab in the 1950s
Many scientists now believe life arose near undersea hydrothermal vents.
However, life may have arisen elsewhere (e.g., Mars) and traveled to Earth!
2 contradictory reasons why scientists generally avoided studying origin of life:
First, __________
Second, _______
2 contradictory reasons why scientists generally avoided studying origin of life:
First, living matter was assumed to be fundamentally different from non-living matter. This idea is called ‘vitalism,’ and it occurs across cultures.
Second, it was also widely believed that life forms from non-living matter all the time! This idea, known as ’spontaneous generation,’ also occurs across cultures. Think maggots.
1924 Alexander Oparin argued that ____ matter was not fundamentally different from ____ matter; the two must be governed by similar ____ and _____ processes.
Many chemists, geologists, biologists began studying origin of life but soon encountered __ difficulties
1924 Alexander Oparin argued that living matter was not fundamentally different from non-living matter; the two must be governed by similar physical and chemical processes.
Many chemists, geologists, biologists began studying origin of life but soon encountered 5 difficulties
5 difficulties on studying origin of life:
5 difficulties on studying origin of life:
1. When life first arose, the Earth was so different from today’s Earth that some of its conditions are difficult to simulate or even to know with certainty. The young Earth was probably, hot, poisonous gases, little oxygen in atmosphere, large meteorites, sun was weak, strong tidal forces
2. The origin of cellular life occurred so long ago that we have little hope of finding actual fossil traces of it. Recall from the last lecture that the Earth’s crust is constantly being recycled by plate tectonics and erosion, leaving very little of the early Earth for us to study
3. Life is everywhere on Earth, from deep in its crust to high in its atmosphere. This means that the modern Earth is no longer conducive for the simple life forms present on early Earth. *problematic because can’t create sterile environment that excludes our modern forms of life
4. All life forms on Earth almost certainly arose from a common ancestor. This means we have no replication to test hypotheses on why life arose.
5. But perhaps the greatest one is how to define life
What are 5 hallmarks of life?
1 homeostasis (the ability to adjust the internal environment to maintain a stable equilibrium)
2. structural organization (the ability to maintain distinct parts and the connections between them)
3. metabolism (the control of chemical reactions)
4. growth and reproduction
5. ability to respond to environmental conditions or stimuli.
Other way to define life
since all life is subject to NS, then if a species can change under NS
What was the first living thing? When did the life first arise on Earth? Where did the first living thing come from?
First living thing was lipid-encapsulated piece of RNA because 1 RNA can self-replicate since RNA serves as a template 2 ribozymes are catalytically active RNA molecules, so RNA uniquely can store info and catalyze its replication
Pros of RNA World hypothesis: solves chicken and egg problem because RNA is info carrier and catalyst for own replication; says that catalytics RNAs were a transitional form between nonliving matter and early cellular life
cons: does not explain where the first RNA molecules came from (RNA is a fairly complex molecule)
Why are we living in a DNA world and not RNA?
DNA is more stable (double helix) and proteins enzymes are more efficient than RNA (Nucleic acid) enzymes
Why is it perhaps not surprising that selection on mating success is stronger than selection on survival?
What makes Earth special?
A Sun of moderate size providing radiant energy over hundreds of millions of years
An orbit that is just the right distance from our Sun, providing the right amount of heat and light, and thus a moderately stable climate
The presence of liquid water
An ozone layer that protects life from harmful ultraviolet rays
Sufficient planetary mass to retain: an atmosphere, an ocean, and a liquid iron core
A liquid iron core, which casts a gigantic magnetic shield into space, protecting life from harmful radiation
The existence of moderate seasons, due to the Earth’s moderate tilt on its axis (23.4°)
A large moon, which stabilizes the Earth’s tilt
Plate tectonics, which creates a diverse environment
What is the law of supposition?
the oldest rocks must lie at the bottom and the youngest at the top.
Steno also noted that rock strata can be identified on the basis of fossils within them.
Later, Georges Cuvier (1769 – 1832) observed that fossils from the youngest strata are more like living organisms than are fossils from lower (older) strata.
What is the principle of uniformitarianism? people?
Hutton and Lyell
The steady, uniform action of the forces of nature could account for the Earth’s features.
This principle was developed as a contrast to catastrophism.
More generally, it can be stated as “the present in the key to the past.”
For geological features to have been produced through such processes, the Earth must be very old.
Darwin came to appreciate how uniformitarianism could explain the evolution of life.
Darwin argued that small changes, accumulating over long periods of time, could produce macroevolutionary change.
Who discovered radiometric dating? What was the problem and solution for finding how old Earth is using this process?
Marie Curie
Problem: no rocks today from Earth’s early history
Solution: use meteorites or moon rocks to date Earth indirectly –> 6.543 B yo
What is the problem for radiometric dating using fossils? How to we determine the age of a fossil?
Problem: Fossils occur only in sedimentary rocks, which cannot be dated directly.
Solution: calculating ages of layers of volcanic ash above and below a fossil
Who proposed continental drift? Explain plate tectonics and why are important for life?
Alfred Wegener
liquid magma push the continental plates of the lithosphere apart. The cooling of magma forms new crust.
Plate tectonics cause continents and their organisms to move over time. create diverse environments that are selective
5 types of fossils
compression
casts and molds
permineralized fossils
unaltered remains
trace fossils
In which environments are organisms least likely to be represented in the fossil record?
mountains then desert
explain fossil biases (3)
1 habitat biases: marine organisms are more likely preserved but actually only 10% of all living species
2 taxonomic biases: fossil record is mainly organisms with hard parts
3 temporal biases: old fossils are very rare
Why do we have few old fossils?
few old fossils because few old rocks –> few old rocks because erosion, plate tectonics, and volcanism
explain chemical remains in fossils
early life have left behind chemical remains that can be found in fossils
organisms produce less heavy carbon (C12) than volcanoes (C13). we can use these ratios as a biomarker for early life
How much of evolution has been caused by life itself?
The Earth (and its component rocks and minerals) have evolved; much of this evolution has been caused by life itself!
How often is it that organisms become fossils?
Organisms only rarely become fossils.
How did cells arise? Aka the first living thing
All life is organized in cells. Cell membranes were selectively favored because they
1 separate internal and external environments
2 provide selective barriers
3 concentrate reactants –> increase reaction efficiency
mutalism?
How does mutualism occur at molecular level>How does mutualism?
when members from 2 or more species interacts in a way that benefits all parties
mutalism forms basis for “hypercycle model” that suggests that if different components are enclosed in a membrane and share collective replication rate, then an increase in the beneficial effect of one component on the replication of another will be favored by NS
*NS favors the ability to compartmentalize components with similar replication rate
Explain the origin of cells
cells may have been formed because of lipid vesicles in water that form bi layered vesicles/droplets. these droplets can grow in response to mechanical agitation.
Dehydrating molecules makes droplets called coacervates that take in only specific chemicals
What is molecular selection?
Selection would have originated as soon as the first non-homogeneous population of molecules appeared on Earth.
What is protocellular selection?
Selection among protocells would have originated as soon as the first non-homogeneous population of protocells appeared (non-homogenous because of differences in size, and/or efficiency in obtaining/utilizing energy).
First living thing was cell
When: 4.1 B
Where: hypothermal vents or extraterrestial
What is wrong with primordial soup hypothesis?
thermodynamically flat… need lots of E or unbalanced to push life up the E hill to make complex polymers RNA, DNA, and proteins
Why hydrothermal vents?
1 black smokers gave protected environment
2 early life was adapted to high temperatures
3 give organic carbon, minerals, and E for complex molecules via releasing small E when H2S reacts with Fe to make FeS
problem: not enough E to make CO2 into organic matter
what is primordial pizza hypothesis?
Explanation for origin of life. Another hypothesis known as the “pizza” hypothesis says that the earliest cells developed on mineral surfaces on land. But this hypothesis can’t explain how those cells would have obtained the right amount of water to survive.
*but plate tectonics are critical for evolution
Cambrian explosion
542 Million y/a
“Why did life suddenly appear?”
*Cambrian explosion is not new species, it’s new phyla! And new ecologies like parasitism and competition
CE = morphology and ecological expansion
Why did cyanobacteria evolve to have pigment?
When life began, there was no oxygen in the atmosphere. With no protective ozone (O3), the Sun’s UV rays sterilized everything on or near the surface.
Cyanobacteria may have initially evolved pigments as a way of absorbing these harmful UV rays.
Once the energy had been absorbed, the cyanobacteria could use this energy to drive chemical reactions; i.e., the process of photosynthesis.
*so something was alive before photosyn but kept on dying because of UV
Great Oxidation Event
2.45 B y/a
rusting of the earth
bounded Fe formation are results of Earth being oxidized/rusted; Bc photosynthesis evolved, and life is making oxygen as byproduct *example of life altering Earth. The O2 binded to Fe in rock then can leave rock and O2 goes into water and makes ozone (O3)
cyanobacteria are a global ____ ____
ecosystem engineer
Eukaryotes appear
2.1 B y/a probably of algae
endosymbiosis (ancestral Euk cells engulfed aerobic bacteria that evolved to become mitochondria; chloroplasts may also have originated this way)
World-wide glaciation
Cryogenian period
850-635 M y/a
cooling period that created ice in whole world
evolution slowed because less heat
Melting of cyrogenian period ice kicks off what?
lots of evolution of life
1st animal
600 y/a 1st animal
sponge is 1st animal; found fossils of embryos in China that have blastula stage (criteria for animals)
larger animals were found 1st when? how do we know?
575-542 Mya
found cholesterol which is only in animals
Did Ediacarans leave any descendants?
placozoans are small, flattened animal that share common ancestor with Ediacarans
phyla represents
different body plans
What caused Cambrian explosion?
1 intrinsic genetic factors: differential gene expression for different cell types because CE is creating complex organisms; cell heredity to maintain different cell lines via methyl transferase enzymes; Homeotic genes (Hox genes) to tell embryo how to grow
2 extrinsic environmental factors: increased temperatures, more oxygen in ocean because photosynthetic algae and more calcium that could create shells
3 extrinsic ecological factors: co-evolution (you either evolve or you go extinct) arising from predator-prey like holes in shells OR competition
What factors might have favored movement onto land?
enabled by?
lots of competition in ocean, so land would be an untapped niche
process enabled by tracheids (elongated cells that move fluids from roots to other plant parts) and stomata to prevent water loss, and genes from bacteria that gave traits to help plants move onto land; animals evolved lungs or tracheal systems for breathing air
Why did trees evolve?
competition for light; different niche (higher up, more sun)
Rhynie Chert
400 Mya
early terrestrial ecosystem
when insects first appeared
tetrapods
370 Mya
4 legs to push them out of oxygen poor water to breathe oxygen
Adaptive radiation occurs when a ____ (or a small ___ of) ancestral lineages ______ rapidly into ____ descendent lineages (‘______’) that occupy a wide variety of ecological niches (‘_____’).
Adaptive radiation requires ____ _____, which can arise from _____ and _____ factors.
Adaptive radiation occurs when a single (or a small group of) ancestral lineages diversifies rapidly into many descendent lineages (‘radiation’) that occupy a wide variety of ecological niches (‘adaptive’).
Adaptive radiation requires ecological opportunity, which can arise from extrinsic and intrinsic factors.
Species, on average, last ______ years before becoming extinct. Such ‘______’ extinction can be caused by many factors that reduce a species’ population size
Species, on average, last a few million years before becoming extinct. Such ‘background’ extinction can be caused by many factors that reduce a species’ population size
Mass extinctions coincide with ____ and _____ environmental change. Mass extinctions are instructive for understanding our current ______ crisis
Mass extinctions coincide with abrupt and global environmental change. Mass extinctions are instructive for understanding our current biodiversity crisis.
Biodiversity refers to:
When studying fossils, we usually measure biodiversity in terms of number of _____ (or higher ____ levels).
Biodiversity refers to the total inherited variation of all organisms
When studying fossils, we usually measure biodiversity in terms of number of genera (or higher taxonomic levels).
Biodiversity has generally _____ over the past 542 million years BUT not _____; lots of _____
Biodiversity has generally increased over the past 542 million years BUT not steady; lots of ups and downs
What are the 2 components of adaptive radiation?
1 production of new species
2 taking up more ecological and morphological space
What is non-adaptive radiation?
speciation without new niches; example: salamanders after warming had to move up in elevation and cannot move into valley because too hot; salamanders were isolated but still radiation because speciation but not AR
What resources could contribute to ecological opportunity?
food, light, resources, space, mates
AR causes
extrinsic (external):
1
2
3
intrinsic:
4
AR causes
extrinsic (external):
1 AR after no competitors initially because space was just created (lakes, mountains)
2 AR after competitors went extinct (ex: dinosaurs)
3 push competitors out because adaptively superior
intrinsic: AR after it evolves a new adaptation to outcompete (ex: herbivore)
An increase in ecological opportunity is a ____ that allows _____ to take place—it is not the trigger of the ______. _____ is the trigger bc…
An increase in ecological opportunity is a condition that allows adaptive radiation to take place—it is not the trigger of the adaptive radiation. Competition is the trigger because it causes pressure for things to move away from each other
Who were the survivors of the crater crash?
small and could burrow underground
what took longer to recover to pre-extinction levels, Pacific ocean ecosystems or phytoplankton?
phytoplankton 8-10 M years
Pacific ocean ecosystems 1.8 M years
mass extinctions tend to _________, with the collapse of primary production cascading up the food chain.
Natural selection cannot prepare species to survive ________
mass extinctions tend to bottom-up, with the collapse of primary production cascading up the food chain.
Natural selection cannot prepare species to survive events that occur only rarely (every tens of millions of years).
Why should biologists explicitly focus on catastrophic bad luck as the major driver of mass extinction?
“Biologists should explicitly focus on catastrophic bad luck as the major driver of mass extinction, and they should deliberately disassociate natural selection from all mass extinction events, including the present one.”
Important because can draw attention to the Earth approaching the 6th mass extinction
Why do we think that there is a 6th mass extinction?
decline in population sizes and genetic diversity because of population bottlenecks –> if environmental change less diversity = less ability to cope and adapt
5 causes:
1 habitat loss, fragmentation, and degradation
2 invasive species
3 pollution
4 climate change
5 over exploitation
