Chapter 3 Notes: Intro to Evolution
Biodiversity: reflects the reality that life on earth exists from the ocean floor to well
into the atmosphere
Ecosystems: group of communities interacting with their shared physical
Community: populations of all species that occupy the same area
Population: Group of individuals of the same kind (that is, the same species) that
occupy the same area
Multicellular organism: individual consisting of interdependent cells
Cell: the smallest unit with the capacity to live and reproduce, independently or as
part of a multicellular organism
Hierarchy of Life: each level exhibits emergent properties that do not exist at lower
Autotrophs: such as plants, synthesize organic carbon molecules using inorganic
Heterotrophs: all animals, they obtain carbon from organic molecules, either from
living hosts or from organic molecules in the products, waste, or remains of dead
Chemotrophs: obtain energy by oxidizing inorganic or organic substances
Phototrophs: obtain energy from light
Chemoautotrophs: carbon source: CO2, inorganic molecules, found in some bacteria
and archaeans; not in eukaryotes
Chemoheterotrophs: carbon source: organic molecules, found in some bacteria and
archaeans, and also in proteins, fungi, animals, and plants
Photoautotroph: carbon source: CO2, energy source: light, found in some
photosynthetic bacteria, in some proteins, and in plants
Photoheterotrophs: carbon source: organic molecules, energy source: light, found in
some photosynthetic bacteria Selection occurs when some force or phenomenon affects the survival of individual
-when a large population of individuals is exposed to a lethal factor and only
resistant individuals survive
-inheritance of offspring
-key factors behind selection: selective force and the capacity for explosive
-major force responsible for evolution and biodiversity
Bacteria that are resistant to antibiotics can survive and reproduce, overwhelming
the defenses of an individual and institutions. Similar to pests and pesticides.
Theory of Evolution
-all organisms alive today descend from a common ancestor, which explains why all
organisms share certain features (unity). It also tells us that species change over
time as a result of natural selection (diversity).
-all organisms use ATP as their cellular energy source, have DNA as genetic material,
and have plasma membranes composed of lipid bilayers
-Central ideas of Darwin’s theory of evolution by natural selection:
1) individual organisms in a population vary in many heritable traits
2) any population has the potential to produce far more offspring than the
environment can support
3) struggle for existence, and some individuals have traits giving them an advantage
in their community
4) more likely to survive and reproduce surviving organisms pass on favourable
traits to their offspring. In this way incidence of traits will change.
Chapter 20 Notes: History of Evolutionary Thought/Evidence for Evolution
-Natural Theology: dominated biological research, sought to name and catalogue all
of God’s creations, i.e. living organisms
-Aristotle’s ladder of life: Great Chain of Being: careful study of species, position, and
-Sir Francis Bacon: established the importance of observation, experimentation, and
-Biogeography, comparative morphology, and geology promoted a growing
awareness of change
-through documentation and findings of fossils, giving rise to the
understanding that the Earth is very old.
-Buffon: proposed some animals must have changed since their creation
-vestigial structures: useless body parts seen today must have had some function in
ancestral organisms -Cuvier: Catastrophism: reasoning that each layer of fossils represented the remains
of organisms that had died in a local catastrophe such as a flood. Repeat of this
happened, forming a different set of fossils in the next higher layer.
-Lamarck: Biological Evolution:
-“perfecting principle” caused organisms to become better suited to their
-simple organisms evolved to more complex ones moving up ladder of life
-Principle of use and disuse: body parts grow in proportion to how much they
are used, unused structures grow weaker and shrink
-Inheritance of acquired characteristics: changes that an animal acquires
during its lifetime are inherited by its offspring.
-his proposed mechanisms do not cause evolutionary change
-Four main contributions:
1) species change through times
2) changes passed from one generation to another
3) organisms change in response to the environment
4) hypothesized the existences of specific mechanisms that caused evolutionary
-James Hutton proposition that slow and continuous physical processes acting over
long periods of time, produced earth’s major geological features.
-Gradualism: view that earth changed slowly over time, contrasted to
-Uniformitarianism: unchanging earth, geologic processes proceed very
slowly, millions of years for landscape to configure.
-Plate tectonics can be responsible for continental drift, and on distribution and
evolution of organisms
-Charles Darwin: - observed species in Galapagos Islands
-animals on different islands varied slightly in form
-artificial selection: breeding individuals with favourable characteristics, so traits
would be enhanced in future generations
1) Physical evidence
2) Evolutionary change occurs in groups of organisms rather than individuals.
Some members survive and reproduce more successfully than others.
3) Multistage process, variations arise within groups, natural selection
eliminates unsuccessful variations and the next generation inherits
4) Some organisms function better in a particular environment
-Natural Selection: mechanism that drives all evolutionary change, acted on the
variability within groups of organisms, favoured traits are preserved, unfavoured
are eliminated. Most fossils found in sedimentary rock, they preserve the details of hard structures
(that are not readily decomposed) such as bones, teeth, shells, wood, leaves, and
pollen of plants.
-Conditions of low oxygen or high acidity are idea for fossilization
-Some fossils are casts or moulds; in others, dissolved minerals replace the original
-Radiometric dating involves the use of isotopes and sometimes allows actual age to
be associated with different rock strata.
-isotopes begin to decay from the moment they form.
-dating is limited by the half-life of the isotope which is the amount of time it takes
half of the initial amount of isotope to decay into more stable elements.
-carbon dating – ratio of Carbon 14 and Carbon 12 to determine fossil age
-living organisms effected by climate and environmental conditions
-plate tectonics: earth’s crust is broken into irregularly shaped plats of rock and
float on mantle, currents cause the plates to move, also known as continental drift.
-Pangaea: supercontinent present on earth 250 million years ago, continental drift is
what separated it into the continents we know today.
-movement of continents towards the poled caused formation of glaciers
-massive volcanic eruptions, asteroids have also impacted climate and atmosphere.
-extinction of many forms of life
Continuous and Disjunct Distributions
-continuous distribution: many species living in suitable habitats throughout large
-disjunct distributions: closely related species live in widely separated locations
-dispersal and vicariance create disjunct distribution
-dispersal: movement of organisms away from their place of origin; disjunct
distribution is produced if a new population becomes established on the far
side of a geographical barrier.
-Vicariance: fragmentation of a continuous geographic distribution by
Biotas: result of geographical isolation of continents, means all organisms living in a
-Wallace’s Biogeographical Realms: Nearctic, Neotropical, Ethiopian, Palearctic,
Oriental, and Australian.
-Endemic Species: species that occur nowhere else on earth, such as marsupials that
are native to Australia.
-Monotremes: egg laying mammals
-Placentals: e.g. bats, rodents, and dingos.
-biotas of Nearctic and palearctic are similar (i.e. North America and Eurasia)
-Convergent Evolution: distantly related organisms that are similar in appearance
not because of a shared ancestor but because they occupy similar environments.
-convergence between placentals and marsupials. Chapter 2: 2.2
-Earth is 4.6 billion years old
-solar system was formed by the gravitational condensation of matter present in a
molecular cloud, which consisted mostly of hydrogen.
-condensation of interstellar gas forms stars
-earth bombarded with rock from solar system (meteorites) , and volcanic and
-the primordial atmosphere contained an abundance of water vapour, H2S, CO2,
NH3, and CH4.
-some were formed spontaneously others were formed by volcanic eruptions
-Oparin and Haldane proposed that organic molecules essential to the formation of
life – including amino acids, sugars, and the nucleotide bases that form DNA and
RNA (could have been made in the absence of life – abiotic synthesis).
-this hypothesis is that the early atmosphere was a reducing atmosphere because of
the presence of large concentration of molecules such as Hydrogen, methane and
-large complex molecules are possible in formulation because the elements above
contain max number of electrons and are said to be fully reduced.
-today’s atmosphere is an oxidizing atmosphere.
The Miller Urey Experiment
-lack of oxygen in primordial atmosphere meant there was no Ozone layer to block
UV light from the sun
-Oparin and Haldane hypothesized that the UV light along with lightning provided
the energy that combined the reducing conditions present in the atmosphere, would
lead to accumulation of simple “building blocks” required for life.
-Miller placed components of a reducing atmosphere – hydrogen, methane,
ammonia, and water vapor – in a closed apparatus and exposed the gases to an
energy source in the form of continuously sparking electrodes.
-Result: large assortment of organic compounds in the water, including Urea, amino
acids, lactic, formic and acetic acids.
--The Miller-Urey apparatus demonstrating that organic molecules can be
synthesized spontaneously under conditions stimulating primordial earth
-When HCN and CH2O were added to the apparatus all the building blocks of
complex biological molecules were produced – amino acids, fatty acids, the purine
and pyrimidine building blocks of nucleic acids, sugars such as glyceraldehyde,
ribose, glucose, and fructose; and phospholipids (form lipid bilayers of membranes)
-scientific debate if there was enough ammonia and methane in the atmosphere
during primitive earth for these things to occur.
-however could have quite possibly occur near volcanoes and hydrothermal vents of
the ocean floor
-organisms near these vents are able to thrive in extreme conditions as well as in the
absence of light.
-polymerization: process in which monomers are linked together to form polymers -doubtful it could have occurred in aqueous environment of primordial earth.
Macromolecules could be easily broken down or hydrolyzed.
-alternative hypothesis: solid surfaces especially clays, would have provided unique
environment for polymerization to occur.
-clay consists of very thin layers of minerals separated by layers of water only a few
-layered structure absorbs ions, and organic molecules and promotes their
interactions, including condensations and other rxns.
-clays can also store potential energy
-term given to a group of abiotically produced organic molecules that are
surrounded by a membrane or membrane-like structure.
-allowed for an internal environment to develop differently than the external one
-concentration of key molecules could be higher and molecules could attain more
order in a closed space
-protobionts could have formed spontaneously on primordial earth
-e.g. liposomes, which are small membrane bound spheres, can be formed when
lipid molecules accumulate in aqueous environment, they ar selectively permeable,
they swell and contract depending on the osmotic conditions
Chapter 17: Microevolution: Genetic Changes within Populations
- Penicillin first antibiotic drug based on naturally occurring substance that
kills bacteria such as Staphylococcus aureus.
- Realization that some bacteria could survive low doses and that the offspring
of those germs would be more resistant to the drug
- Streptococcus pneumonia is leading cause of infectious death world-wide
- How do bacteria become resistant to antibiotics?
- Genomes of bacteria vary among individuals, some bacteria have genetic
traits that allow them to withstand attack by antibiotics
- Surviving bacteria reproduce and resistant organisms become more common
in later generations
- Process of selection
- Evolution of antibiotic resistance in bacteria is an example of
microevolution: heritable change in the genetics of a population
- Population: all individuals of a single species that live together in the same
place and time.
17.1: Variation in Natural Populations
- Phenotypic variation: differences in appearance or function that are passed
from generation to generation. 17.1a: evolutionary biologists describe and quantify phenotypic variation
- Quantitative variation: individuals differ in small, incremental ways
- This data is displayed in a bar graph or if sample is large enough as a curve.
Displaying continuous variation among members of a population.
- The width of the curve is proportional to the variability – the amount of
variation – among individuals, and the mean describes the average value of
- Qualitative variation: they exist in two or more discrete states, and
intermediate forms are often absent.
- Polymorphism: the existence of discrete variants of a character. E.g. human
blood groups (A, B, AB, and O)
- Phenotypic polymorphisms are expressed quantitatively by calculating
percentage or frequency of each trait.
17.1b: Phenotypic Variation Can Have Genetic and Environmental Causes
- Phenotypic variation within populations may be caused by genetic
differences b/w individuals, by differences in the environmental factors
individuals experience, or by an interaction between genetics and the
- E.g. of environmental effects: soil acidity effects the expression of the gene
controlling flower colour in the common garden plant hydrangea
macrophylla. Acidic soil produces blue, neutral produces pink.
- Some circumstances, organisms with different genotypes exhibit the same
- Organisms with the same genotype sometimes exhibit different phenotype.
- Only genetically based variation is subject to evolutionary change.
- Breeding experiments can demonstrate the genetic basis of phenotypic
17.1c: Several Processes Generate Genetic Variation
- Genetic Variation: two potential sources: production of new alleles and the
rearrangement of existing alleles.
- new alleles probably arise from small-scale DNA mutations
- rearrangement of existing scales into new combinations can result from larger
scale mutations in chromosome structure, genetic recombination, including crossing
over b/w homologous pairs in meiosis, independent assortment of non-homologous
chromosomes, and random fertilization of genetically different sperm and eggs
17.1d: Populations Often Contain Substantial Genetic Variation
- Gel electrophoresis to identify polymorphisms in diverse organisms
- Technique separates two or more forms of a given protein if they differ
significantly in shape, mas or net electrical charge - Identification of a protein polymorphism by inferring genetic variation at the
locus coding for that protein.
- Result: much genetic variations
17.2a: All Populations Have a Genetic Structure
- Gene Pool: sum of all alleles at all gene loci in all individuals
- Genotypic Frequencies: percentages of individuals possessing each
- Allele Frequencies: abundances of one allele relative to others at the same
gene locus in individuals of a population.
- Relative abundances: relative commonness of populations within a
17.2b: Hardy Weinberg Principle
- Null Models: predict what they would see if a particular factor has no effect,
they serve as theoretical reference points against which observations can be
- Hardy Weinberg Principle: specifies the conditions under which a population
of diploid organisms achieves genetic equilibrium, the point at which neither
allele frequencies nor genotype frequencies change in succeeding
- Mathematical model that describes how genotype frequencies are
established in sexually reproducing organisms.
- Conditions: 1) no mutations occurring. 2) The population is closed to
migration from other populations. 3) The population is infinite in size. 4) all
genotypes in the population survive and reproduce equally well. 5)
Individuals in the population mate randomly with respect to genotypes
- If conditions are met, allele frequencies will never change, and genotype
frequencies will stop changing after one generation
- Therefore, microevolution will not occur
17.3: Agents of Microevolution
- Population’s allele frequencies will change overtime if conditions of Hardy
Weinberg Principle are not met.
- Agents of microevolution: mutation, gene flow, genetic drift, natural
selection, and nonrandom mating
17.3a: Mutations create new genetic variations
- Mutation: heritable change in DNA, which introduces new genetic variation
- Deleterious mutations: alter an individual’s structure, function, or behavior
in harmful ways - Lethal mutations: cause the death of organisms carrying them, if a lethal
allele is dominant, both homozygous and heterozygous carriers suffer effects.
If recessive it affects only homozygous recessive individuals.
- Neutral mutations: neither harmful nor helpful – amino acid sequence not
- Advantageous mutation: confers some benefit on an individual that carries it,
natural selection might preserve the new allele and even increase its
frequency over time.
17.3b: Gene Flow Introduces Novel Genetic Variants into Population
- gene flow: The transfer of genes from one population to another through the
movement of individuals or their gametes.
- dispersal agents e.g. pollen carrying wind or seed carrying animals responsible for
gene flow in most plant populations
- phenotypic or genetic markers to identify immigrants in a population, to
demonstrate they reproduces and contributed to the gene pool of their adopted
- many immigrant females do not foster gene flow because they do not contribute to
the gene pool of the population they join.
- evolutionary importance of gene flow depends on the degree of genetic
differentiation b/w populations and the rate of gene flow b/w them.
17.3c: Genetic Drift Reduces Genetic Variability within Populations
- Genetic Drift: random fluctuations in allele frequency as a result of chance events;
usually reduces genetic variation in a population
- Has especially dramatic effects on small populations, violating Hardy-Weinberg
Principle assumption of infinite population size
- chance deviations from expected results - which cause genetic drift – occur
whenever organisms engage in sexual reproduction, simply because their
population sizes are not infinitely large
- particularly common in small populations because only a few individuals
contribute to the gene pool and b/c any given allele is present in very few
- genetic drift leads to the loss of alleles and reduced genetic variability
- population bottlenecks and founder effects, foster genetic drift
- Population bottlenecks: a stressful factor such as disease, starvation, or drought
kills a great many individuals and eliminates some alleles from a population,
producing a population bottleneck.
-this reduces genetic variation even if the populations numbers later rebound
- Founder Effect: when a few individuals colonize a distant locality and start a new
population, carry only a small sample of the parent populations genetic variation
-by chance some alleles may be missing from the new population while other rare
ones might appear more frequently
-genetic drift has important implications for conservation ecology -endangered species experience sever population bottlenecks which result in the
loss of genetic variability
-limited genetic variation, as well as small numbers, threatens populations of
17.3d: Natural Selection Shapes Genetic Variability by Favouring Some Traits Over
- Natural Selection: process by which such traits become more common in
subsequent generations. (Violates Hardy Weinberg Principle)
- Can change the allele frequencies, it is the phenotype of an individual
organism, rather than any particular allele, that is successful or not.
- Reproduction causes both favourable and unfavourable traits to be passed on
to the next generation.
- Relative fitness: number of surviving offspring that an individual produces
compared with number left by others in the population.
- Directional Selection: when individuals near one end of the phenotypic
spectrum have the highest relative fitness
- Shifts trait away from mean to a more favoured extreme.
- Stabilizing Selection: individuals expressing intermediate phenotypes have
the highest relative fitness
- Reduces genetic and phenotypic variation and increases the frequency of the
- Most common mode of natural selection
- Disruptive Selection: when extreme phenotypes have higher relative fitness
than intermediate phenotypes
- Favours both extreme phenotypes, promoting polymorphism
- Much less common
17.3e: Sexual Selection Often Exaggerates Showy Structures in Males
- Sexual Selection: has fostered the evolution of showy structures such as
brightly coloured feathers, long tails, or impressive antlers – as well as
elaborate courtship behavior in the males of many animal species
- Intersexual selection: selection based on the interactions b/w males and
- Intrasexual selection: selection based on the interactions b/w members of
the same sex. i.e. males use their large body size, antlers, tusks, to intimidate,
injure, or to kill rival males.
- Sexual selection is the most probable cause of sexual dimorphism,
differences in the size or appearance of males and females
- Sexual selection pushes phenotypes toward one extreme 17.3f: Nonrandom Mating Can Influence Genotype Frequencies
- HW assumption – individuals must select mates randomly with respect to
- Many organisms do however mate non-randomly, selecting a mate with a
particular phenotype and underlying genotype
- Because individuals with similarly genetic based phenotypes mate with each
other, the next generation will contain fewer heterozygotes
- Inbreeding: form of nonrandom mating in which individuals that are
genetically related mate with each other
- Organisms that live in a small/closed populations tend to mate with relatives
- Inbreeding increases the frequency of homozygous genotypes and decreases
the frequency of heterozygotes. Recessive alleles are often repressed.
17.4a: Diploidy Can Hide Recessive Alleles from the Action of Natural Selection
- diploid condition reduces the effectiveness of natural selection in eliminating
harmful recessive alleles from a population
- such alleles might be disadvantageous in homozygous state, they may have
zero or no effect in heterozygous state
- recessive alleles can be protected from natural selection by the phenotypic
expression of the dominant allele
- diploid state preserves recessive alleles at low frequencies, in large
- in small populations, a combination of natural selection and genetic drift can
eliminate harmful recessive alleles
- when a recessive allele is common, most copies are present in homozygotes,
when the alleles is rare, most copies exist as heterozygotes
- rare alleles that are completely recessive are protected from the action of
natural selection because they are masked by dominant alleles in
17.4b: Natural Selection Can Maintain Balances Polymorphisms
- Balanced Polymorphism: one in which two or more phenotypes are
maintained in fairly stable proportions over many generations.
- Natural selection preserves it when heterozygotes have higher relative
fitness, when difference alleles are favoured in different environments, and
when the rarity of a phenotype provides an advantage.
- Heterozygote Advantage: a balances polymorphism can be maintained,
when heterozygotes for a particular locus have higher relative fitness than
- e.g. maintains of the HbS (sickle) allele , which codes for a defective form of
hemoglobin in humans
- it is an oxygen transporting molecule in red blood cells - low oxygen causes the red blood cells to take a sickle shape
- most common in regions with malarial parasites infect red blood cells in
40.10: Mates as Resources
- Mating Systems: maximize reproductive success, in response to the amount
of parental care that offspring require and other aspects of species’ ecology.
- Monogamy: a male or female form a pair bond for a mating season or for the
individuals entire reproductive lives.
- Polygamy: occurs when one male has active pair bonds with more than one
female (polygyny) or one female has active pair bonds with more than one
- Promiscuity: occurs when males and females have no pair bonds beyond the
time it takes to mate
40.11: Sexual Selections
- Sexual dimorphism in which one gender is larger or more colourful than
another can be an outcome of sexual selection
- Adornments or weapons can attract other females, and ward off other males
- A males large size, large horn, bright feathers, might indicate that the male is
healthy, harvest resources efficiently, or simply manage to survive to an
- His features signify his quality/genetic makeup that he can potentially
fertilize a females eggs with successful alleles
- Can potentially gain access to large territories and resources
- Males locate cluster of females and fight to keep others away, those who can
inseminate the most females means they will increase their offspring’s
chances of living long enough to reproduce
- In some populations, females have a more active mate choice…they inspect
potential male partners
- Lek: a display ground where males each possess a small territory from which
they court attentive females
- E.g. a peahens mate choice influences her offspring’ chances of survival –
peacocks with more attractive tails tend to survive and mate with more
19.1a Fake Flowers
- The fungus, Puccinia monoica, affects the growth of leaves, changing their
appearance and odour making it flower-like and appear to produce nectar
19.1b Carnivorous Plants
- Plants use different methods to trap insects for nitrogen - Not all carnivorous plants share a common ancestor
19.1c Mammals with Flat Tails Are Not Always Beavers
- Fossil found of: Castorcauda lutrasimilis mammal that had modified tail
vertebrae fattened like living beavers – but beavers are not the only
mammals with flat tails
- Flowerlike structures are not always flowers, carnivorous plants are not
necessarily closely related, and looking a mammals tail may give you a
different picture of its relationship than its skull
- Although the tails of aquatic mammals with flattened tails are broad and flat
with similarities in caudal vertebrae, the skills and teeth are different
19.2 Systematic Biology: Overview
- Systematic biology, classification, and taxonomy help us organize and
understand info about the biological world
- Two majors goals of Systematics: 1) reconstruct the phylogeny or
evolutionary history of a group of organisms.
- Phylogenies are represented in phylogenetic trees, which are formal
hypotheses identifying likely relationships among species
- Accurate phylogenetic trees are used to compare and analyze the
- It allows us to distinguish similarities from a common ancestor from those
that evolved independently in response to similar environments
- 2) Taxonomy: identification and naming of species their placement in a
- Classification: an arrangement of organisms into hierarchical groups that
reflect their relatedness
19.3 The Linnaean System of Classification
- Linnaeus described and named thousands of species on the basis of their
similarities and differences
- Taxonomic hierarchy: arranging organisms into categories based on family
(group of genera that closely resemble one another), Orders, Classes, Phyla,
and into Kingdoms.
- Lastly all life on earth is classified into three domains and organisms
included into any category of the taxonomic hierarchy compromise a taxon
19.5. Evaluating systematic Characters
- Systematists seek characters that are independent markers of underlying
genetic similarity and differentiation
- Stugy traits in which phenotypic variation reflects genetic differences – try to
exclude differences caused by environmental conditions - Must be genetically independent, reflecting different parts of organisms’
- Systematic analyses rely on the comparison of homologous characters as
indicators of common ancestry and genetic relatedness
- Analogous characters are homoplasious (homoplasies), phenotypic
similarities that evolved independent in different lineages
- Homoplasies: characteristics shared by a set of species often because they
live in similar environments but not present in their common ancestor, often
the product of convergent evolution
- Systematists exclude homoplasies from their analysies because they provide
no information about shared (genetic) ancestry
- Homologous bones, different structures and functions
- Homologous characters emerge from comparable embryonic structures and
grow in similar ways during development
- Mosaic evolution: refers to the reality that in all evolutionary lineages, some
characteristics evolve slowly, whereas others evolve rapidly
- Ancestral characters: old forms of traits, and derived characters (new form of
traits) are displayed in species as a mixture
- Presence of a vertebral column is a derived character because fossils of the
earliest animals lack backbones
19.6 Phylogenetic Inference and Classification
- phylogenetic trees portray the evolutionary diversification as a hierarchy
that reflects branching pattern of evolution
- each branch represents the descendants of a single ancestral species
- monophyletic taxa: those derived from a single ancestral species
- polyphyletic taxa: species from separate evolutionary lineages
- paraphyletic taxa: ancestor and some, but not all, of its descendants
- assumption of parsimony: that the simplest explanation should be most
- unlikely same changes evolved twice in one lineage
- traditional evolutionary systematics: groups together species that share
ancestral and derived characters
- Cladistics produces phylogenetic hypotheses and classifications that reflect
only the branching pattern of evolution. It ignores morphological divergence
- Cladists group together species that share derived characters
- Clade: a monophyletic group of organisms that share homologous features
derived from a common ancestor
- Cladograms are phylogenetic trees illustrating a hypothetical ancestor at
each branching point
- Always display monophyletic groups and use principle of parsimony - Phylocode: identifies and names clades instead of placing organisms into the
familiar taxonomic groups
19.7: molecular data
- most systematists use molecular characters as part of the data set when
conducting phylogenetic analyses
- molecular data include nucleotide base sequences of DNA and RNA or the
amino acid sequences of the proteins for which they code
- because DNA is inherited it provides clues to the evolutionary relationships
- Advantages: 1) provide abundant data because every amino acid in a protein
and every base in a nucleic acid can serve as a separate character for analysis
- 2) molecular sequences can be compares between distantly related
organisms that share no organismal characteristics – as well as study closely
related species with morphological differences
- 3) many proteins and nucleic acids are not directly affected by the
developmental or environmental factors that cause non-genetic
- Disadvantage: since there are only 4 nucleotide bases at each position in DNA
or RNA sequence and only 20 possible amino acids. If two species have the
same base substitution, their similarity may have evolved independently –
therefore making it difficult to verify if they evolved from a single common
- Molecular clock: a technique for dating the time of divergence of two species
or lineages, based on the number of molecular sequence differences between
- Mosaic evolution occurs at a molecular level, so different molecules exhibit
individual rates of change
- Mitochondrial DNA evolves relatively quickly, useful for dating evolutionary
divergences that occurred within the last few million years
- Chloroplast DNA and genes that encode ribosomal DNA evolve much more
slowly, providing info for divergences that are hundreds of millions of years
- Species that diverged recently from a common ancestor should share many
similarities in their molecular sequences, whereas more distantly related
species should exhibit few similarities
- Amino acid sequencing allows systematists to compare the primary structure
of protein molecules directly
- When two species exhibit similar amino acid sequences for the same protein,
systematists, infer their genetically similar and evolutionary related 19.7c
- insertion or deletion of base pairs can change the length of a DNA sequence
and the relative locations of the specific positions along its length
- therefore, systematists align the sequences they are comparing to ensure
that the nucleotide base being compared are at the exact same position
- by determining where insertions or deletions have occurred, systematists
match up the positions of the nucleotides
18.1: What’s in a Name?
- communication can affect both inter- and intra- specific behavior
- biologists use scientific names (Latinized descriptions) of the organism
bearing the name, for precise communication
18.2 Definition of Species
- Species are the fundamental taxonomic units of biological classification.
Environmental laws are framed in terms of species.
- 1)Biological Species Concept defines species as a group of organisms that
can successfully interbreed and produce fertile offspring
- 2)The Phylogenetic Species Concept defines a species as a group of
organisms bound by a unique ancestry
- 3)The Ecological Species Concept defines a species as a group of organisms
that share a distinct ecological niche
- Problems with the definitions: 1) it deals only with species that reproduce
sexually, and ignores ones that reproduce asexually. Reproduction patterns
can blur the definition of species
- Androdioecous organisms exist as natural populations of functional males
and hermaphrodites but include no true females
- Gynogenetic species have only females – use internal fertilization, by which
they seduce males for their sperm to stimulate the eggs and achieve
- These two examples do not fall under the biological species concept does this
mean they are not species?
- 2)The definition also does not apply where there is hybridization (when two
species interbreed and produce fertile offspring).
- Hybridization b/w species that produces sterile offspring does not put them
outside the definition
- Sterile hybrids result when horses are crossed with zebras and lions with
tigers. Mules are the sterile hybrids of donkeys and a female horse, where as
hinnies are sterile hybrids of a male horse and a female donkey
- Asexually reproducing populations had a higher frequency of mutations in
mitochondrial protein-coding genes than sexually repr