Evolution
A Darwinian View of Life (ch. 22)
Traditional Views (22.1)
Descent with Modification (22.2)
Scientific Evidence (22.3)
Greek Philosophers
suggested that life might have changed gradually over time
Aristotle
viewed species as fixed, unchanging
recognized certain "affinities" among organisms and concluded that life-forms could be arranged on a ladder
Scala naturae
Scale of nature
increased complexity of the organism where every organism had its own spot
consistant with the Old Testament and suggested that individuals were designed perfect by God
Carolus Linnaeus
developed the two-part, or binomial, format for naming species
Example: Homo sapiens
adopted a classification system
grouped similar species into increasingly general categories
Example: similar species are grouped in the same genus, similar genera are grouped in the same family, and so on
Darwin argued the classification should be based based on evolutionary relationships
turned to Paleontology
the study of fossils
fossils
the remains or traces of organisms from the past
typically found in sedimentary rocks formed from sand and mud that settle to the bottom of seas, lakes, and swamps
layers of the sediment are called strata
upper strata were the younger fossils
lower strata were the older fossils
Georges Cuvier
noted that the older the stratum , the more dissimilar its fossils were to current life-forms
observed that some new species appeared while others disappeared
inferred that the boundaries between strata represented a sudden catastrophic event
Lamarck's Hypothesis of Evolution
proposed a mechanism for how life changes over time
found several lines of descent, each chronological series of older to younger fossils leading to a living species
Two principles
Use and Disuse
Inheritance of acquired characteristics
the idea that parts of the body that are used extensively become larger and stronger, while those that are not used, deteriorates
Example: a giraffe stretching its neck to reach leaves on high branches
organism could pass these modifications to its offspring
Observations
Members of a population often vary in their inherited traits
All species can produce more offspring than their environment can support, and many of these offsprings fail to survive and reproduce
genetic variation
Inferences
individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offsprings
Unequal ability to survive and reproduce will lead to the accumulation of favorable traits in the population over generations
Natural Selection
a process in which individuals that have certain heritable traits survive and reproduce at a higher rate than do other individuals because of those traits
Adaptation
inherited characteristics of organisms that enhance their survival and reproduction in specific environment
Examples : The finches' various beaks and behaviors are adapted to the specific foods available on their home islands
The unity of Life
unity of life to the descent of all organisms from an ancestor that lived in the remote past
gradually accumulated diverse modifications , or adaptations, that fit them to specific ways of life .
can increase the frequency of adaptations that are favorable in a given environment
may result in adaptations to new conditions if the environment is disturbed or a species moves to a new environment
overpopulation occurs
Artificial Selection
Microevolution
Macroevolution
pattern of evolution above the species level
focusing on evolutionary changes in populations
selecting and breeding individuals that posses desired traits
Evolution of Drug-Resistant Bacteria
The Evolution of Populations (CH 23)
Genetic Variation makes evolution possible (23.1)
Hardy-Weinberg Equation (23.2)
Altering allele frequency in a population (23.3)
Natural Selection causes adaptive evolution (23.4)
Staphylocuccus
Anatomical and Molecular Homologies
Homology
related species can have characteristics that have an underlying similarity yet function differently.
Homologous structures
Example:forelegs, flippers, and wings of different mammals
represent variations on a structural theme that was present in their common ancestor
Vestigial Structures
permanent features that served a function in the organism's ancestor
these structures are no longer useful for present day species
Example: Snake with pelvis
Example: Human with appendix
Evolutionary Tree
A diagram that reflects evolutionary relationships among groups of organisms
are hypotheses that summarize our current understanding of patterns of descent
supported by anatomical and DNA sequence data
can be used to makes surprising predictions about organisms
Convergent Evolution
the independent evolution of similar features in different lineagaes
The resemblance is said to be analogous
Analogous
features share similar functions, but not common ancestors
share common ancestors but not necessarily similar functions
The Fossil Record
documents the pattern of evolution, showing that past organisms differ from present day organisms and that many species have become extinct
provides evidence of evolutionary changes that have occurred in various groups of organisms
shows that over time , descent with modification produced increasingly large differences among related groups of organism
Biogeography
the scientific study of the geographic distributions of species
Continental Drift
the slow movement of Earth's continents over time
Pangaea
these movements united all of Earth's landmasses into a single large continent
has no negative effect on the organism it harbors on
Strain Methicillin-resistant S. aureus are formidable pathogens
Penicillin was used to treat bacteria which eventually became resistant to the medicine
The Origin of Species
Genetic Variation
characters that vary in this way are determined by a single gene locus, with different alleles producing distinct phenotypes
many phenotypic characters are influenced by multiple genes
Example: coat color in horses
Example: seed number in corn
Example: height in humans
can be measured at the molecular level of DNA ( nucleotide variability)
many nucleotide variations occur within introns
non coding segments of DNA lying between exons
the regions retained in mRNA after RNA processing
Phenotypes
Physical characteristics
Formation of New alleles
can arise by mutation
a change in the nucleotide sequence of an organism's DNA
Point Mutation
a change of as little as one base in a gene
can have a significant impact on the phenotype
Generally result in neutral variation
differences in DNA sequence that do not confer a selective advantage or disadvantage
in multi cellular organisms, only mutations in cell lines that produce gametes can be passed to offspring
Altering Gene number or position
chromosomal changes that delete, disrupt, or rearrange many loci are usually harmful
one mutation in every 100,000 genes per generation, often even lower in prokaryotes
prokaryotes have more generations per unit of time, so mutations can quickly generate genetic variation in their population
Sexual Reproduction
genetic variations results from the unique combination of alleles that each individual receives from its parents
crossing over
during meiosis, homologous chromosomes, one inherited from each parent, trade some of their alleles by crossing over
distributed at random through gametes
rearranges existing alleles into fresh combinations each generation, providing much of the genetic variation that makes evolution possible
a way to test whether evolution is occurring in a population
a population is a group of individuals of the same species that live in the same area and interbreed, producing fertile offsprings
populations have gene pools
consists of all copies of every type allele at every locus in all members of the population
if only one allele exists for a particular locus in a population, that allele is said to be fixed in the gene pool, and all individuals are homozygous for that allele
named for the British mathematician and German physician, respectively, who independently developed this idea in 1908
in a population that is not evolving, allele and genotype frequencies will remain constant from generation to generation,
p^2+2pq+q^2=1
p^2= expected frequency of genotype EX: Cr Cr
2pq; expected frequency of genotype Ex; CrCw
q^2; expected frequency of genotype Ex; CwCw
Conditions for Hardy-Weinberg Equilibrium
No mutations
Random Mating
No natural Selection
Extremely large population size
No gene flow
in small populations, allele frequencies fluctuate by chance over time ( a process called genetic drift.)
allele frequencies change when individuals with different genotypes show consistent differences in their survival or reproductive success
if individuals mate within a subset of the population, random mixing of gametes does not occur and genotype frequencies change
The gene pool is modified if mutations occur or if entire genes are delected or duplicated
By moving alleles into or out of populations, gene flow can alter allele frequencies
Natural Selection
Genetic Drift
The founder effect
The Bottleneck Effect
Genetic drift is significant in small populations
chance events can cause an allele to be disproportionately over- or underrepresented in the next generation.
can cause allele frequencies to change at random
an allele may increase in frequency one year, then decrease the next; the change from year to year is not predictable
can lead to a loss of genetic variation within populations
genetic drift can eliminate alleles from a population. can effect how effectively a population can adapt to a change in environment
can cause harmful alleles to become fixed
alleles that are neither harmful nor beneficial can be lost or become fixed by chance through genetic drift.
when a few individuals become isolated from a larger population, this smaller group establish a new population whose gene pool differs from the source population
Example: when a few members of a population are blown by a storm to a new island
genetic drift , in which chance events alter allele frequencies
a sudden change in the environment that drastically reduce the size of a population
Example: Fire or flood
individuals in a population exhibit variations in their heritable traits, and those with traits that are better suited to their environment tend to produce more offspring
Adaptive evolution
process in which traits enhance survival or reproduction tend to increase in frequency over time
Relative Fitness
the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals
Directional Selection
Disruptive selection
stabilizing selection
shifting a population's frequency curve for the phenotypic character in one direction or the other .
acts against both phenotypes and favors intermediate variants
occurs when conditions favor individuals at both extremes of a phenotype range over individuals with intermediate phenotype
Sexual Selection
a process in which individuals with certain inherited characteristics are more likely than other individuals of the same sex to obtain mates
can result in sexual dimorphism
a difference in secondary sexual characteristics between males and females of the same species
Example: size, color, ornamentation, and behavior
Intrasexual selection
selection within the same sex, individuals of one sex compete directly for mates of the opposite sex
Intersexual selection
mate choice
individuals of one sex (usually females) are choosy in selecting their mates from the other sex
balancing selection
selection itself may preserve variation at some loci, thus maintaining two or more phenotypic forms in a population
frequency-dependent selection
the fitness of a phenotype depends on how common it is in the population
Speciation can take place with or without Geographic Separation (Ch. 24.2)
Biological species concept emphasizes reproductive isolation (Ch. 24.1)
Speciation can occur rapidly (Ch. 24.4)
a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring
do not produce viable, fertile offspring with members of other such groups
Reproductive isolation
the existence of biological factors that impede members of two species from interbreeding and producing fertile offspring
barriers block gene flow between species and limit the formation of hybrids
offsprings that result from an interspecific mating
Prezygotic barriers
block fertilization from occurring in three ways
impeding members of different species from attempting to mate
preventing an attempted mating from being completed successfully
hindering fertilization if mating is completed successfully
Habitat Isolation
two species that occupy different habitats within the same area may encounter each other rarely
Temporal Isolation
species that breed during different times of the day, different seasons, or different years cannot mix their gametes
Behavioral Isolation
Courtship that attracts mates and other behaviors unique to a species are effective reproductive barriers
Example:The geographic ranges of the western spotted skunk and the eastern spotted skunk overlap
Blue-footed boobies do the "high step" to show females off their blue feet
Example: two fly species, one feeds on apples and the other feed on oranges will never encounter each other
Mechanical Isolation
Mating is attempted, but morphological differences prevent its successful completion
Example: A Husky and a chihuahua
Postzygotic Barriers
may contribute to reproductive isolation after the hybrid zygote is formed
Reduced Hybrid Viability
The genes of different parent species may interact in ways that impair the hybrid's development or survival in its environment
Reduced Hybrid Fertility
hybrids may be sterile, may also fail to produce normal gametes
Hybrid Breakdown
first-generation hybrids are viable and fertile, but when they mate with another or with parent species, offsprings of the next gen are feeble or sterile
Morphological species concept
distinguishes a species body shape and other structural features
Allopatric Speciation
gene flow is interrupted when a population is divided into geographically isolated subpopulations
Sympatric speciation
speciation occurs in populations that live in the same geographic area
can occur if gene flow is reduced by such factors as polyploidy, sexual selection , and habitat differentiation
polyploidy
a species may originate from an accident during cell division that results in extra sets of chromosomes
occurs in animals
example: the gray tree frog Hylaversicolor is thought to have originated in this way
autoploidy
allopolyploidy
an individual that has more than two chromosomes sets that are all derived from a single species
Example: a failure of cell division could double a cell's chromosome number from the original number to a tetraploid number
when sterile hybrids change into fertile polyploid
fertile when mating but cannot interbreed with either parent species, thus represent a new biological species
reinforcement
involves reinforcing reproductive barriers
Punctuated Equilibrium
sudden changes
new species can form rapidly once divergence begins but it takes millions of years
Gradual equilibrium
a slow transition
the time interval between speciation events considerably, from a few thousand years to tens of million years
researchers have identified particular genes involved in some cases of speciation
speciation is driven by few or many genes
In very small population genetic drift can also cause alleles that are slightly harmful to become fixed