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Chapter 20
3. Provide evidence to support the hypothesis that chemical evolution resulting in life's origin
occurred in 4 stages:
a. Abiotic synthesis of organic monomers Abiotic synthesis is a testable hypothesis. Laboratory
experiments performed under conditions simulating those of the primitive Earth have produces
diverse organic molecules from inorganic precursors. Stanley Miller and Harold Urey used an
apparatus to stimulate chemical dynamics on the primitive Earth. A warmed flask of water
simulated the primeval sea. The "atmosphere" consisted of H2O, H2, CH4, and NH3. Sparks
were discharged in the synthetic atmosphere to mimic lightning. A condenser cooled the
atmosphere, raining water and any dissolved compounds back to the miniature sea. As material
circulated through the apparatus, the solution in the flask changed from clear to murky brown.
After one week, Miller and Urey anayzed the contents of the solution and found a variety of
organic compounds, including some of the amino acids that make up the proteins of organisms.
b. Abiotic synthesis of polymers Laboratory simulations of the early Earth conditions have
produced organic polymers. Small organic molecules polymerize when they are concentrated on
hot sand, rock, or clay. This process vaporizes water and concentrates the monomers on the
substratum. Using this method, Sidney Fox of the University of Miami had made what he calls
Proteinoids, which are polypeptides produced by abiotic means. Perhaps waves or rain splashed
dilute solutions of organic monomers onto fresh lava or other hot rocks on the early Earth and
then rinsed proteinoids and other polymers back into the water.
c. Formation of protobionts Protobionts can form by self-assembly. Organic molecules
synthesized in the laboratory have spontaneously assembled into a variety of droplets microspheres, liposomes, and coarcervates - with some of the properties associated with life.
d. Origin of genetic information The first genes may have been abiotically produced RNA, whose
base sequence served as a template for both alignment of amino acids in polypeptide synthesis
and alignment of complementary nucleotide bases in a primitive form of self-replication. Once
genetic information became incorporated inside membrane-enclosed compartments, protobionts
would have acquired heritability and the ability to evolve as units.
4. Describe Whittaker's five-kingdom system.
The traditional five-kingdom system classifies organisms as Monera (prokaryotes), Protista
(relatively simple eukaryotes), Plantae, Fungi, and Animalia (this criterion originally used by
Whittaker.)
5. Describe three alternatives to the five-kingdom system and explain the rationale for each.
The six kingdom alternative divides the prokaryotes into two kingdoms. This modification is
based onmolecular evidence for an early evolutionary divergence between eubacteria (most
bacteria) and archaebacteria, an ancient lineage of prokaryotes with many unique
characteristics.
The next alternative puts more significance to the ancient evolutionary split between eubacteria
and archeabacteria by using a superkingdom taxon called the domain.
The eight-kingdom system is one example of a "kingdom-splitting" solution to the taxonomic
problems posed by certain distinct lineages of microorganism. In addition to two separate
prokaryotic kingdoms, this system also splits the protists into three kindgoms.
Chapter 22
1. State the two major points Darwin made in The Origin of Species concerning the Earth's biota.
The Darwinian view of life can be dissected into two separate claims: the evolution of new
species by descent with modification from ancestral species, and natural selection as the
mechanism for this evolution.
3. Describe Carolus Linnaeus' contribution to Darwin's theory of evolution.
Linnaeus, who apparently believed that species are fixed, provided Darwin with a connection
to evolution by recognizing that the great diversity of organisms could be ordered into "groups
subordinate to groups." (kingdom>phylum>class>order>family>genus>species) To Darwin, the
natural hierarchy of the Linnean scheme reflected the branching genealogy of the tree of life,
with organisms at the different taxonomic levels related through descent from common
ancestors.
7. Describe Jean Baptiste Lamarck's model for how adaptations evolve.
Before Darwin, Jean Baptiste Lamarck proposed an evolutionary theory to account for the
fossil record. His suggested mechanism was the inheritance of acquired characteristics. Lamarck
saw the ground level of the ladder of life as the microscopic organisms, which Lamarck believed
were continually generated spontaneously from inanimate material. At the top of the
evolutionary escalators were the most complex plants and animals. Evolution was driven by an
innate tendency toward the greater and greater complexity, which Lamarck seemed to equate
with perfection.
11. Explain what evidence convinced Darwin that species change over time.
Each generation, environmental factors screen heritable variations, favoring some over
others. Differential reproduction results in the favored traits being disproportionately represented
in the next generation. Darwin found evidence in artificial selection, the breeding of
domesticated plants and animals. Humans have modified other species over many generations
by selecting individuals with the desired traits as breeding stock.
13. Explain why variation was so important to Darwin's theory.
Natural selection involves interactions between individual organisms and their environment, but
individuals do not evolve. Evolution can be measured only as changes in relative proportions of
variations in a population over a succession of generations. Natural selection can only amplify or
diminish those variations that are heritable.
Heritable variation is at the heart of Darwin’s theory of evolution, for variation provides the
substrate on which natural selection works.
15. Define and state the basic principles in natural selection.
Natural selection is based on differential success in reproduction, made possible because of
variation among the individuals of any population and the tendency for a population to produce
more offspring than the environment can support. On average, the individuals best adapted to
the local environment leave the most offspring and thereby pass on their adaptive characteristics.
Natural selection involves interactions between individual organisms and their environment, but
individuals do not evolve. Evolution can be measured only as changes in relative proportions of
variations in a population over a succession of generations. Natural selection can only amplify or
diminish those variations that are heritable.
17. Using some contemporary examples, explain how natural selection results in evolutionary
change.
One investigation of natural selection in action tests a beak evolution of Darwin’s finches.
The medium ground finch uses its strong beak to crush seeds. Given a choice of small needs or
large seeds, the birds eat mostly small seeds. During wet years, small seeds are produced in
such abundance that ground finches consume relatively few large seeds. This changes during
dry years when the birds resort to eating a larger proportion of large seeds. Field studies
comparing offspring to parents confirm that this trait is inherited rather than acquired. The most
likely explanation is that those birds that happen to have stronger beaks have a feeding
advantage during droughts and pass the genes for this trait to their offspring.
Another investigation is a change in taste by a Western butterfly, testing the feeding of the Edith
editha on Collinsia torreyi, a common native plant in a Nevada meadow.
20. Describe how molecular biology can be used to study the evolutionary relationships among
organisms.
Closely related species show unmistakable similarities in their DNA and proteins.
21. Explain the problem with the statement that Darwinism is "just a theory". Dismissing Darwin’s
theory as "just a theory" has two flaws. First, it fails to separate Darwin’s two claims: that
modern species evolved from ancestral forms, and that natural selection is the main mechanism
for this evolution. The conclusion that life has evolved is based on historical evidence. So the
"just a theory" argument concerns Darwin’s second claim, his theory of natural selection. As
applied to evolution, the term theory refers to models for how to evolution occurs.
Chapter 23
1. Explain what is meant by the "modern synthesis".
Modern synthesis is a comprehensive theory of evolution emphasizing natural selection,
gradualism, and populations as the fundamental units of evolutionary change; also called neoDarwinism.
2. Explain how micro-evolutionary change can affect a gene pool.
Microevolution, a change in allele or genotype frequencies in a population, can occur when
the conditions required for Hardy-Weinberg equilibrium are not met.
3. In their own words, state the Hardy-Weinberg theorem.
The Hardy-Weinberg theorem describes a non-evolving population. According to the HardyWeinberg theorem, the frequencies of alleles in a population will remain constant if sexual
reproduction is the only process that affects the gene pool. The mathematical expression for
such non-evolving population is the Hardy Weinberg equation, which states that for a two-allele
locus, p^2 +2pq+q^2 = 1, where p and q represent the relative frequencies of the dominant
and recessive alleles, respectively, p^2 and q^2 the frequencies of the homozygous genotypes,
and the 2pq and the frequency of the heterozygous genotype.
7. Describe the usefulness of the Hardy-Weinberg model to population geneticists. The HardyWeinberg model is useful to population geneticists by the Hardy-Weinberg equation enabling the
calculation of frequencies of alleles in a gene pool if the frequencies of genotypes are known, and
vice versa. 9. Explain how genetic drift, gene flow, mutation, nonrandom mating and natural
selection can cause microevolution. Genetic drift can cause evolution via chance fluctuation in a
small populations gene pool. Genetic drift is the change in allele frequencies observed in small
populations due to sampling error or chance events.
Gene flow can cause evolution by transferring alleles between populations. Gene flow is the
exchange of alleles between two populations due to migration.
Mutations can cause evolution by substituting one allele for another in a gene pool. Mutation can
theoretically affect allele frequencies in a gene pool, but it is usually insignificant over the short
term for large populations. Mutation is mainly important in evolution because it generates new
variations.
Nonrandom mating can cause evolution by shifting the frequencies of genotypes in a gene pool.
Nonrandom mating, such as inbreeding or assortative mating, does not ordinarily affect allele
frequencies, but does affect the ration of genotypes in populations.
Natural selection can cause evolution via differential reproductive success among varying
members of a population. Natural selection is the only agent of microevolution that tends to be
adaptive.
11. Distinguish between the bottleneck effect and the founder effect.
The bottleneck effect is the genetic drift resulting from the reduction of a population,
typically by a natural disaster, such that the surviving population is no longer genetically
representative of the original population.
The founder effect is a cause of genetic drift attributable to colonization by a limited number of
individuals from a parent population.
12. Explain why mutation has little quantitative effect on a large population Mutation does not
have much quantitative effect on a large population in a single generation. This is because a
mutation at any given gene locus is a very rare event; although mutation rates vary, mutation
per locus per 10^5 to 10^6 gametes are typical.
18. Give the cause of nearly all genetic variation in a population.
Both discrete and quantitative characters contribute to variation within a population. Most
heritable variation consists of polygenic characters that vary quantitatively within a population.
Polymorphism is a cause of nearly all genetic variation where polymorphic characters existent.
19. Explain how genetic variation may be preserved in a natural population.
The tendency for natural selection to reduce variation is countered by several mechanisms
that preserve or restore variation. Diploidy and Balanced Polymorphism preserve variation. The
ability of natural selection to maintain diversity in a population is called balanced polymorphism.
One of the mechanisms for this preservation of variation is heterozygote advantage.
24. Describe what selection acts on and what factors contribute to the overall fitness of a
genotype.
Selection favors certain genotypes in a population by acting on the phenotype of individual
organisms. The whole organism is the object of selection.
25. Give examples of how an organism's phenotype may be influenced by the environment.
I am familiarized with how an organism’s phenotype may be influenced by its environment.
26. Distinguish among stabilizing selection, directional selection and diversifying selection.
Natural selection can affect the frequency of a phenotype in three different ways: stabilizing
selection, which discriminates against extreme phenotypes; directional selection, which favors
relatively rare individuals on one end of the phenotypic range; and diversifying selection, which
favors individuals at both extremes of a range over intermediate phenotypes.
28. Give at least four reasons why natural selection cannot breed perfect organisms. Evolution by
natural selection does not fashion perfect organisms for several reasons: Structures result from
modified ancestral anatomy, adaptations are often compromises, the gene pool can be affected
by genetic drift, and natural selection can act only on available variation.
Chapter 24
3. Define biological species (E. Mayr).
The biological species concept defines a species as a population or group of populations
whose members have the potential to interbreed with one another in nature to produce viable,
fertile offspring, but who cannot successfully interbreed with members of other species.
4. Describe some limitations of the biological species concept.
The biological species concept does not work in all situations. The criterion of interbreeding
is useless for organisms that are completely asexual in their reproduction, as are all prokaryotes,
some protists, some fungi, and even some plants and some animals. The biological species
concept is also inadequate as a criterion for grouping extinct forms of life, the fossils of which
must be classified according to morphology.
6. Distinguish between prezygotic and postzygotic isolating mechanisms.
Prezygotic barriers impeded mating between species or hinder the fertilization of ova if members
of different species attempt to mate. In particular, species that occupy the same geographic are
often live in separate habitats (habitat isolation); breed at different times (temporal isolation);
possess unique, exclusive mating signals and courtship behaviors (behavioral isolation); and/or
have anatomical incompatible reproductive organs (mechanical isolation) or incompatible sex
cells (gametic isolation).
Even if species manage to mate, postzygotic barriers usually prevent the interspecific hybrids
from developing into adults, breeding with either parent species, or producing viable fertile
offspring.
7. Describe five prezygotic isolating mechanisms and give an example of each.
In particular, species that occupy the same geographic are often live in separate habitats
(habitat isolation); breed at different times (temporal isolation); possess unique, exclusive
mating signals and courtship behaviors (behavioral isolation); and/or have anatomical
incompatible reproductive organs (mechanical isolation) or incompatible sex cells (gametic
isolation).
10. Distinguish between allopatric and sympatric speciation.
Allopatric speciation is a mode of speciation induced when the ancestral population becomes
segregated by a geographical barrier.
Sympatric speciation is a mode of speciation occurring as a result of a radical change in the
genome that produces a reproductively isolated subpopulation in the midst of its parent
population.
13. Describe the adaptive radiation model and use it to describe how it might be possible to have
many sympatric closely related species even if geographic isolation is necessary for them to
evolve.
Adaptive radiation is the evolution of numerous species with diverse adaptations from a common
ancestor. Island chains are showcases of radiation. See Figure 22.8 (page 443) for the model for
adaptive radiation on island chains.
1 - One island in the cluster of the three is seeded by a small colony founded by individuals of
Species A, blown over from a mainland population.
2 - Its gene pool isolated from the parent species, the island population evolves into Species B as
it adapts to its new environment.
3 - Storms or other agents of dispersion spread species B to a second island
4 - where the isolated colony evolves into species C.
5 - Later, individuals from Species C re-colonize the first island and cohabit with species B, but
reproductive barriers keep the species distinct.
6 - A colony of species C may also populate a third island
7 - where it adapts and forms species D
8 - species D is dispersed to the two islands is dispersed to the two islands of its ancestors
9 - forming a new species, E, on one of those islands.
14. Define sympatric speciation and explain how polyploidy can cause reproductive isolation.
Sympatric speciation occurs without geographic separation when a segment of the
population experiences a genetic change that results in reproductive isolation. Sympatric
speciation is most common in plants, in which the mutation is usually the doubling of the
chromosome number.
16. List some points of agreement and disagreement between the two schools of thought about
the tempo of speciation (gradualism vs. punctuated equilibrium).
According to the theory of punctuated equilibrium, a species changes most when it buds from an
ancestral species and then remains fairly static in morphology for the rest of its duration.
One view of speciation is that it usually occurs gradually by an accumulation of microevolutionary changes in gene pools.