Unit 7: Natural Selection (AP BIO)
What do fossils provide evidence of?
changing life forms
strata
layers of rock where fossils are deposited
Charles Lyell
geologic processes that have shaped planet = uniform over time -> Earth must be older than previously thought (a few thousand years)
Jean Baptiste de Lamarck
proposed a mechanism for evolution based on use and disuse & inheritance of acquired characteristics
Use and disuse
Inheritance of acquired characteristics
characteristics acquired in lifetime -> passed onto next generation
(flawed theory)
What was the significance of Lamarck's findings?
recognized that species evolve; organisms and environment match through this gradual evolutionary change
inheritance of acquired characteristics - wrong
What was the significance of Lyell's findings?
an old Earth has time for evolution; a young Earth doesn't -> gave Darwin the "gift of time"
Example of inheritance of acquired characteristics
A weightlifter's child could be born with a more muscular anatomy
What was the impetus for the development of Darwin's evolution by natural selection?
Darwin's voyage on the HMS Beagle
Natural Selection
results in alleles being passed to the next generation in proportions different from their relative frequencies in the present generation
Adaptations
Example of an adaptation
Darwin's theory of evolution: principle one
members of a population often vary in their inherited phenotypic traits
Darwin's theory of evolution: principle two
Darwin's theory of evolution: principle three
individuals with inherited traits that are better suited to local environment = more likely to survive and reproduce
"differential reproductive success"
Fitness
the reproductive success of an individual in a population
Darwin's theory of evolution: principle four
evolution -> unequal reproductive success of individuals -> accumulation of favorable traits in the population over generations
What does natural selection improve over time?
the match between organisms and their environment
If individuals move to a new environment, or their environment changes...
natural selection may result in adaptation to these new conditions
different genetic variations can be selected depending on...
the new environment
Individuals DO NOT EVOLVE...
populations evolve
Evolution
a change in the genetic makeup of a population over time
Artificial selection
process by which species are modified by humans
Example of artificial selection
selective breeding for milk or meat production; development of dog breeds
Evidence for Evolution
Direct observations of evolutionary change
examples of direct observation of evolutionary change
Homology
characteristics in related species can have an underlying similarity even though they have very different functions
Homologous structures
anatomical signs of evolution
examples of homologous structures
present and used in a common ancestor
Embryonic homologies
example of embryonic homologies
all vertebrate embryos have a post-anal tail and pharyngeal pouches
Vestigial organs
example of vestigial organs
Molecular homologies
examples of molecular homologies
Convergent evolution
explains why distantly related species can resemble one another
The likenesses that result from convergent evolution are considered...
analogous, not homologous
examples of convergent evolution
"similar problems have similar solutions"
paleontology
the study of fossils
Fossil record
succession of forms!
transitional fossils have been found that...
link ancient organisms to modern species
Biogeography
the geographic distribution of species
Species in a discrete geographic area...
tend to be more closely related to each other than species in distant geographic areas
example of biogeography (as evidence for evolution)
Continental drift & the breakup of Pangaea
Endemic species
found at a certain geographic location and nowhere else
example of endemic species
phenotypic variation often reflects...
genetic variation
examples of phenotypic variation
Mutations
only source of new genes and new alleles
only mutations in cell lines that produce...
gametes can be passed to offspring
Point mutations
Example of a point mutation
sickle cell disease
Chromosomal mutations
gene duplications can...
most genetic variations within a population result from...
the sexual recombination of alleles that already exist in a population
sexual reproduction...
shifts existing alleles and deals them at random to produce individual genotypes
three mechanisms for the shuffling of alleles
Population
a group of Individuals of the same species that live in the same area and interbreed, producing fertile offspring
Population genetics
the study of how populations change genetically over time
Gene pool
all of the alleles at all loci in all the members of a population
How many alleles does for a particular gene does each Individual have (diploid species)
two (and the individual may be heterozygous or homozygous)
Fixed (pertaining to a gene)
all members of a population are homozygous for the same allele
the greater number of fixed alleles...
the lower the species' genetic diversity
Hardy-Weinberg equation
used to describe a population that is not evolving
Hardy-Weinberg Equilibrium
1) no change in allelic frequency due to mutation
2) random mating
3) no natural selection
4) extremely large population size
5) no migration
What is the Hardy-Weinberg equation good for?
provides an excellent null hypothesis (conditions are seldom met in natural populations)
three major factors that alter allele frequencies...
(and bring about the most evolutionary change)
Differential Reproductive Success
Adaptive evolution
organisms adapted to their environment
Genetic Drift
unpredictable fluctuation in allele frequencies from one generation to the next
the smaller the population...
the greater the chance there is for genetic drift
two examples of genetic drift
Founder effect
a few individuals become isolated from a larger population and establish a new population whose gene pool is not reflective of the source population
Example of the founder effect
a mat of vegetation washes up on the shore of a Pacific island, host to a small population of lizards
Bottleneck effect
a sudden change in the environment that drastically reduces the size of a population
Example of the bottleneck effect
Gene flow
occurs when a population gains or loses alleles by genetic additions or subtractions from the population (often by migration)
gene flow occurs when...
alleles between different populations are mixed, resulting in a reduction of genetic differences between the populations
gene flow tends to reduce the...
genetic differences between populations, making them more similar
converse of gene flow
isolated populations do not experience it, tend to adapt to their unique environments and may have significant genetic differences from the ancestral population
Relative fitness
the contribution an organism makes to the gene pool of the next-generation relative to the contributions of other members
fitness in the context of evolution is only measured...
by reproductive success
natural selection acts more directly on the...
phenotype
natural selection acts more indirectly on the...
genotype
Three ways in which natural selection can alter the frequency distribution of heritable traits
Directional selection
Example of directional selection
Disruptive selection
Example of disruptive selection
Stabilizing selection
Example of stabilizing selection
Sexual selection
Sexual dimorphism
How is genetic variation preserved in a population? (Why doesn't natural selection eliminate all unfavorable alleles?)
Diploidy
Heterozygote advantage
Example of heterozygote advantage
Why does natural selection not produce perfect organisms?