Chapters 22-24
Chapter 22 - Descent with Modification: A Darwinian View of Life
Early Classification
Scala Naturae
Linear Hierarchy
"Scale of Nature"
Aristotle
Life forms arranged on a ladder, increasing complexity.
Binomial Naming Format
Carolus Linnaeus
Nested Classification System
Grouped similar species into increasingly general categories.
Ex. "Homo Sapiens" : Humans
Changing Ideas
Darwin
Drew from studies of fossils (Paleontology)
Found in Strata (Stratum)
Sedimentary Rocks
Georges Cuvier
James Hutton
Noted dissimilar fossils in older stratum, compared to modern life-forms
Believed each boundary between strata marked a sudden catastrophe.
Opposed idea of Evolution
Proposed geological features formed by gradual mechanisms.
Charles Lyell
Proposed the same geologic processes are operating today, as in the past.
Lamarck's Hypothesis
Use and Disuse
Inheritance of acquired characteristics
Body parts become stronger with use and deteriorated with disuse
Organisms could pass modifications to offspring
Ex. "Giraffes stretching their necks to reach branches."
Ex. "Giraffes evolved over generations stretching their necks higher."
Descent with Modification Explains Adaptions
Darwin's Research
Went to medical school, later joined Cambridge university to become a Clergyman
Voyage of Beagle
Observed and collected specimens
Noted similarities and differences of mocking birds in Galapagos
Hypothesized Galapagos had been colonized by south america, then diversified.
Focus on Adaption
Observed examples of adaption
Inherited characteristics that enhance survival and reproduction in specific environments.
Natural Selection
Process by which individuals with specific inherited traits tend to survive and reproduce at a higher rat, because of those traits.
"The Origin of Species"
Written by Charles Darwin
Descent with Modification
All organisms descend from a related ancestor, from the distant past, and developed modifications to fit specific ways of life.
Viewed history of life as a tree with many "branches"
Selection and Adaption
Artificial Selection
Selective breeding of domesticated animals
Results in organisms with little resemblance to wild ancestors
Used to prove natural selection
Natural Selection
Observations
#⃣ 1
Members of a population often vary in their inherited traits
#⃣ 2
All species produce more offspring than their environment can support, many do not survive to reproduce.
Inferences
#⃣ 1
#⃣ 2
Individuals whose inherited traits give them a higher probability of surviving/ reproducing tend to leave more offspring in a given environment.
Unequal ability of individuals to survive/ reproduce leads to accumulation of favorable traits in population over generations
Adaptation
An organisms traits influence it's own performance, and offspring's.
Advantageous variations gradually accumulate in the population, less favorable variations diminish
Over time, process increases frequency of individuals with favorable adaptations
Support of Evolution
Direct observations
Natural selection in response to introduced species
"beaks" of soap berry bugs changing in response to introduction of new food sources
Evolution of Drug Resistant Bacteria
Pathogens reproduce quickly
Results in more mutations that can be advantageous
Homology
related species have characteristics with underlying similarities, but different functions
Anatomical & Molecular
Convergent Evolution
Homologous Structures
Evolutionary Tree
Vestigial Structures
All life forms use same genetic code
Structures in different species that look similar due to a common ancestor
Remnants of features that served a function in an organism's ancestors.
Homologous Genes can
Acquire new functions
Retain original functions
Lose their function
Diagram reflecting evolutionary relationships among groups of organisms
Independent evolution of similar features in different lineages.
Analogous Features
Features share similar function, not ancestry
Fossils
Documents pattern of Evolution
Shows, over time, descent with modification produced increasingly large differences between related groups of organisms
Biogeography
Scientific study of geographic distribution of species
Continental Drift
Pangaea
Endemic
Slow movement of earth's continents over time
Single super continent made up of all earth's land masses
Found nowhere else in the world
Chapter 23 - Evolution of populations
Genetic Variation makes Evolution Possible
Genetic Variation
Sources of Genetic Variation
Differences in composition of individuals genes/DNA sequence
Phenotypic Variation
How genetic variations are expressed
Mendel's pea plants; Purple or White flowers
Introns
Non-coding segments of DNA
Exons
Coding segments of DNA
Part of DNA that gets transcribed
Formation of new Alleles
Mutation
A change in nucleotide sequence of an organisms DNA
Neutral Variation
Differences in DNA sequence that doesn't have a selective advantage or disadvantage
Aka. Mutations with no noticeable effect
Altering Gene Number/Position
Rearrangement
Rapid Reproduction
Sexual Reproduction
Duplication
Chromosomal changes; deletes, disrupts or rearranges loci
Duplication of genes in meiosis
Uneven crossing over
"slippage" during DNA replication
activities of Transposable elements
Mutation Rates
Low in plants/animals
Lower in prokaryotes
Have lower generation times
Mutations generate genetic variation quickly
Shuffles existing alleles, deals them at random to produce individual genotypes
Crossing over
Independent assortment of chromosomes
Fertilization
Hardy Weinberg Equations
Gene Pool & Allele Frequency
Population
Hardy-Weinberg Equations
Gene Pool
Group of individuals of same species that live in same area & interbreed, producing viable fertile offspring
Some populations are geographically isolated
A population's genetic make up
Consists of all copies of every type of allele, in every member of population
Fixed Allele
All Individuals Homozygous for allele
Allele Variation
Two or more alleles for loci exist in population
Individuals may be homozygous or heterozygous
Hardy-Weinberg Equilibrium
Populations, not currently evolving, allele & genotype frequency remain constant
p+q=1
p = Frequency of Dominant Allele (%)
q = Frequency of Recessive Allele (%)
p^2+2pq+q^2=1
p^2 = Frequency of Homozygous Dominant Individuals
2pq = Frequency of Heterozygous Individuals
q^2 = Frequency of Homozygous Recessive Individuals
Conditions
No mutations
Random mating
No natural selection
Extremely large population size
no gene flow
Alterations in allele frequencies in Populations
Natural Selection
Genetic Drift
Gene Flow
Results in alleles being passed down to the next generation
Proportions differ from that of older generations
Adaptive Evolution
Traits that enhance survival/reproduction tend to increase in frequency over time
Chance events cause unpredictable fluctuations in allele frequency from one generation to another
Bottle Neck Effect
Size of a population is greatly reduced in a short period of time, remains population no longer reflects original population.
Alleles may be over represented, under represented, or completely absent
Flounder Effect
A few individuals become isolated, forming a larger with a different gene pool than the original population
Effects
Significant in small populations
Can cause allele frequencies to change at random
can lead to the loss of genetic variation within a population
can cause harmful alleles to become fixed
Transfer of genes into or out of a population, due to the movement of fertile individuals or their gametes
Natural Selection: A Closer Look
Selection Types
Why can't nature fashion perfect organisms?
Relative Fitness
Contribution an individual makes to the gene pool of next generation relative to contributions of other individuals
Selection can only act on existing variations
Evolution is limited by historical constraints
Adaptions are often compromises
Chance, natural selection and environment interact
Stabilizing Selection
Sexual Selection
Disruptive Selection
Balancing Selection
Directional Selection
population favors variants of one extreme phenotype in a specific environment
Population lives in environment that favors both extremes over intermediate phenotypes
Environment favors populations with an intermediate phenotype over extreme variants
Individuals with certain inherited traits make an individual more likely to obtain mates
Sexual Dimorphism
Differences of secondary sex characteristics between males and females
Size, Color, Ornamentation, Behavior...
Intrasexual Selection
Individuals of the same sex compete for mates of the opposite sex
Intersexual Selection
"Mate Choice"
Members of one sex are particularly choosy when selecting a mate
Selection that maintains two or more phenotypic forms in a population
Frequency-Dependent Selection
Fitness of a phenotype is dependent on how frequent it is in the population
Heterozygote Advantage
Greater reproductive success of heterozygous individuals, compared to homozygous
maintains two or more alleles in population
Chapter 24 - The Origin of Species
"Mystery of species"
Speciation
Process by which one species splits into two or more species
Microevolution
Changes over time in allele frequencies in a population
Macroevolution
The broad pattern of evolution above the species level
Reproductive Isolation Emphasis
Definitions of Species
Biological Species Concept
Reproductive Isolation
Existence of biological factors that impede members of two species from interbreeding and producing viable, fertile offspring.
Hybrids
Offspring that result from an interspecific mating
Reproductive Barriers
Prezygotic Barriers
"Before the Zygote"
Habitat isolation
Two species can occupy different habitats in the same area and thus may never encounter each other.
Temporal isolation
Some species breed at specific times of day/ year and thus won't be able to mix their gametes
Behavioral isolation
Some species have unique behaviors/ courtship rituals to attract mates, each specific to that particular species
Mechanical isolation
Mating may be attempted but morphological differences prevent successful completion
Postzygotic Barriers
"After the Zygote"
Reduced Hybrid Viability
Genes of different parents may interact in ways that impair the hybrid's development/ survival
Reduced Hybrid Fertility
Hybrid Breakdown
Genes of different parent may have chromosomal differences resulting in hybrids unable to produce viable gametes
Some first generation hybrids are viable and fertile, but after mating with each other or one of the parent species, the next generation is feeble or sterile
A group of populations, whose members are able to interbreed and produce viable, fertile offspring
Morphological Species Concept
Distinguishes a species by body shape and other structure features
Ecological Species Concept
Defines species in terms of it's ecological niche
Doesn't require information on gene flow
Relies on subjective criteria
The sum of how members of species interact with living and nonliving parts of their environment
Emphasizes role of disruptive natural selection
Speciation without Geographic Separation
Allopatric Speciation
allos , "other" ; Patra , "Homeland"
Geneflow is interupted when population is divided into geographically isolated subpopulations
Process
Geographic isolation occurs
Separated gene pools diverge
Mutations
Natural Selection
Generic Drift
Reproductive isolation
Sympatiric Isolation
Syn , "Together"
Speciation occurs in populations living in the same geographic area
Polyploidy
Accident during cell division results in an extra set of chromosomes
Autopolypoid
individual with more than two chromosomal sets that are derived from a single species
Allopolypoid
individual with more that two chromosomal sets from two different species.
can interbreed with each other, but not parent species
Sexual selection
Females select males based on appearance and can act as a reproductive barrier
keeps gene pools of two species seperate
Habitat Differentation
A subpopulation exploits a habitat or resource not used by the parent population
Hybrid Zones
A region in which members of a different species meet and mate, producing at last some offspring of mixed ancestry
Patterns
some zones form as narrow bands
typically resemble isolated patches scattered about
Over Time
Hybrids can become reproductively isolated and form a new species
Reinforcement
Hybrids are often less fit than members of the parent species
natural selection strengthens prezygotic barriers to reduce formation of such hybrids
Fusion
Gene flow through hybrid zones causes speciation to reverse.
two species' gene pools become so alike, until they fuse into one species.
Stability
Hybrids continue to be produced with little to no effect on the parent populations
Time Course of Speciation
Patterns in Fossil Record
Punctuated Equilibria
Long periods of apparent stasis, species undergo little to no morphological change, interrupted by brief periods of sudden change
Gradual
Species diverge from one another slowly and steadily over time