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CHAPTER 22
DESCENT WITH MODIFICATION:
A DARWINIAN VIEW OF LIFE
OBJECTIVES
1. State the two major points Darwin made in The Origin of Species concerning the Earth's
biota.
2. Describe Carolus Linnaeus' contribution to Darwin's theory of evolution.
3. Describe Jean Baptiste Lamarck's model for how adaptations evolve.
4. Explain what evidence convinced Darwin that species change over time.
5. Explain why variation was so important to Darwin's theory.
6. Define and state the basic principles in natural selection.
7. Using some contemporary examples, explain how natural selection results in evolutionary
change.
8. Describe how molecular biology can be used to study the evolutionary relationships among
organisms.
9. Explain the problem with the statement that Darwinism is "just a theory".
ANSWERS:
1. Darwinism has dual meaning. One facet is recognizing of evolution as the explanation of life’s
unity and diversity. The second facet is the Darwinian concept of Natural selection as the cause
of adaptive evolution.
2. 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”.
3. Lemarck believed that evolution was driven by an innate tendency toward increasing
complexity, which he equated with perfection. As organisms attained perfection, they became
better and better adapted to their environments. Thus, Lamark believed that evolution
responded to organisms’ felt needs.
4. Darwin perceived the origin of new species and adaptation as closely related processes; new
species could arise from an ancestral population by gradually accumulating adaptations to a
different environment. For example, two populations of species could be isolated in different
environments as each adapted to local conditions.
5. Variation was important to Darwin’s theory because if he did not have a variation of different
animals and living things to relate to his theory then he would not have had enough evidence to
support it and it would never have become anything.
6. a) Populations possess an enormous reproductive potential. Darwin calculated that two
elephants would produce a population of 19 million individuals after 750 years if all offspring
survived to reproductive maturity and fostered their normal number of offspring.
b) Population sizes remain stable. Darwin observed that populations generally fluctuate
around constant size.
c) Resources are limited. Resources, such as food, water, or light, do not increase, as
populations grow larger.
d) Individuals compete for survival. Eventually, the needs for a growing population will exceed
the available resources. As a result, individuals must compete for resources.
e) There is variation among individuals in a population. Most traits reveal considerable variety
in their form. In humans, for example, skin, hair, and eye color occur as continuous variation
from very dark to very light.
f) Much variation is heritable. Most traits are produced by the action of enzymes that are
coded by DNA. DNA is the hereditary information that is passed from generation to generation.
g) Only the most fit individuals survive. “Survival of the fittest” occurs because individuals with
traits best adapted for survival in the environment are able to outcompete other individuals for
resources.
h) Evolution occurs as advantageous traits accumulate. The best adapted individuals survive
and leave offspring who inherit the traits of their of their parents. In turn, the best adapted of
these offspring leave the most offspring. Over time, traits best adapted for survival in the
environment and the alleles that generate them accumulate in the population.
7. One example would be, Peter and Rosemary Grant’s study of medium ground finches on
Daphne Major, a tiny islet of the Galapagos. They discovered that the average depth of beaks in
this finch population changes over the years. During droughts, beak depth increases, only to
decrease again during wet periods.
8. Molecular signs of evolution discussed in chapter 5 were basically saying that evolutionary
relationships among species are reflected in their DNA and proteins. In their genes and gene
products. If two species have libraries of genes and proteins with sequences of monomers that
match closely, the sequences must have been copied from a common ancestor. A common
genetic code is further evidence that all life is related.
9. The “just a theory” argument concerns Darwin’s second claim, his theory of Natural selection.
This brings us to the second flaw in the “just a theory” case. The term theory has a very different
meaning in science compared to our general use of the word. The colloquial use of “theory”
comes close to what scientists mean by a “hypothesis.”
CHAPTER 23
THE EVOLUTION OF
POPULATIONS
OBJECTIVES
1. Explain what is meant by the "modern synthesis".
2. Explain how micro-evolutionary change can affect a gene pool.
3. In your own words, state the Hardy-Weinberg theorem.
4. Describe the usefulness of the Hardy-Weinberg model to population geneticists.
5. Explain how genetic drift, gene flow, mutation, nonrandom mating and natural
selection can cause microevolution.
6. Distinguish between the bottleneck effect and the founder effect.
7. Explain why mutation has little quantitative effect on a large population.
8. Give the cause of nearly all genetic variations in a population.
9. Explain how genetic variation may be preserved in a natural population.
10. Describe what selection acts on and what factors contribute to the overall fitness of a
genotype.
11. Distinguish among stabilizing selection, directional selection and diversifying selection.
12. Give at least four reasons why natural selection cannot breed perfect organisms.
ANSWERS:
1. A comprehensive theory of evolution that became known as the modern synthesis was forged
in the early 1940’s. It is called a synthesis because it integrated discoveries and ideas from
many different fields, including paleontology, taxonomy, biogeography, and, of course,
population genetics.
2. Micro-evolutionary change can affect a gene pool because, if there is even a slight change in
the living thing, it has undergone evolution. So, even the smallest change, like microevolutionary change, could affect the evolutionary path of the living thing.
3. There has to be a very large population size, Isolation from other populations, No net
mutations, Random mating, and Natural selection.
4. It describes the genetic structure of non-evolving populations.
5. Microevolution is caused by these examples because they affect the allele frequencies in the
population. They also introduce a change in the alleles or genotypes.
6. A bottleneck occurs when the population undergoes a dramatic decrease in size. Regardless
of the cause of the bottleneck (natural catastrophe, predation, and disease), the small
population that results becomes severely vulnerable to genetic drift. Destructive geological or
meteorological events such as floods, volcano eruptions, and ice ages have created bottlenecks
for many populations of plants and animals.
The founder effect occurs when allele frequencies in a group of migrating individuals are, by
chance, not the same as that of their population of origin. For example, one of the founding
members of the small group of Germans that began the Amish community in Pennsylvania
possessed an allele for polydactylism (more than five fingers or toes on a limb). After 200 years
of reproductive isolation, the number of cases of this trait among the eight thousand Amish,
exceed the number of cases occurring in the remaining world’s population.
7. By itself, 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, depending on the species and the gene locus, rates of one mutation per
locus 105 to 106 gametes are typical.
8. Genetic variation, are caused by non-random mating, natural selection, genetic drift, and
mutations.
9. There are two subjects that branch off from preservation of genetic variation. They are
Diploidy and Balanced Polymorphism. The diploid nature of most eukaryotes hides a
considerable amount of genetic variation from selection in the form of recessive alleles in
heterozygotes. Selection itself may preservevariation at some gene loci. This 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.
10. An organism exposes it phenotype, its physical traits, metabolism, physiology, and behavior
to the environment. Acting on phenotypes, selection indirectly adapts a population to its
environment by increasing or maintaining favorable genotypes in the gene pool. The factors that
contribute to the overall fitness is whether or not they are doing the proper things to “stay in
shape” or eating correctly, the same as any other living thing.
11. Stabilizing selection culls extreme variants from the population. The trend is toward reduced
phenotypic variation and maintenance of the status quo.
Directional selection shifts the overall make up of the population by favoring variants of one
extreme.
Diversifying selection favors variants of opposite extremes over intermediate individuals.
12. With the constraints stated on page 433, we cannot expect evolution to craft perfect
organisms. Natural selection operates on a “better than” basis. We can see evidence for
evolution in the subtle imperfections of the organisms it produces.
CHAPTER 2 4
THE ORIGIN OF SPECIES
OBJECTIVES
1. Define biological species (E. Mayr).
2. Describe some limitations of the biological species concept.
3. Distinguish between prezygotic and postzygotic isolating mechanisms.
4. Describe five prezygotic isolating mechanisms and give an example of each.
5. Distinguish between allopatric and sympatric speciation.
6. 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.
7. Define sympatric speciation and explain how polyploidy can cause reproductive isolation.
8. List some points of agreement and disagreement between the two schools of thought about
the tempo of speciation (gradualism vs. punctuated equilibrium).
ANSWERS:
1. 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.
2. 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.
3. Prezygotic barriers impede mating between species or hinder the fertilization of ova if
members of different species attempt to mate. If a sperm cell from one species does fertilize an
ovum of another species, then postzygotic barriers prevent the hybrid zygote from developing
into a viable, fertile adult.
4. Habitat: live in separate habitats. Behavorial: posses unique, exclusive mating signals and
courtship behavior. Temporal: breed at different times. Mechanical: have anatomically
incompatible reproductive organs. Gametic: have incompatible sex cells.
5. The initial block to gene flow may be a geographical barrier that physically isolates the
population. This speciation is termed allopatric speciation. In the second speciation mode, a
subpopulation becomes reproductively isolated in the midst of its parent population; this is
sympatric speciation.
6. Adaptive radiation is the rapid evolution of many species from a single ancestor. This
happens when the ancestral species colonize areas with diverse geographic or ecological
conditions. Variations of the ancestral species become populations specialized for each set of
conditions.
7. Polyploidy is the possession of more
than the normal two sets of chromosomes found in
diploid cells. Normal meiosis in the tetraploid individual will continue to produce diploid gametes,
reproductive Isolation with other individuals in the population occurs in a single generation.
CHAPTER 26
EARLY EARTH AND
THE ORIGIN OF LIFE
OBJECTIVES
1. Provide evidence to support the hypothesis that chemical evolution resulting in life's origin
occurred in 4 stages:
a. Abiotic synthesis of organic monomers
b. Abiotic synthesis of polymers
c. Formation of protobionts
d. Origin of genetic information
2. Describe Whittaker's five-kingdom system.
3. Describe three alternatives to the five-kingdom system and explain the rationale for each.
ANSWERS:
1. a) because of Miller and Urey’s experiment, it was proven that the amino acids needed to
begin life and some bases of DNA and RNA could be formed in the primordial soup.
b) In some lab experiments, polymerization has occurred by dripping diluted solutions of organic
molecules onto hot rocks. Waves or rain could have diluted these, splashing them onto fresh lava or
hot rocks.
c) These could have preceded living cells. Lab experiments show that they can form
spontaneously. When cool water is added, they become miproteinoids (swelling or shrinking in a
salt water solution like cells do).
d) In a lab, if RNA is transferred to a test tube solution containing monomers to make more
RNA, nucleotides of 5-10 base pairs can be formed.
2. The five-kingdom system recognizes the two fundamentally different types of cell, prokaryotic
and eukaryotic, and sets the prokaryotes apart from all eukaryotes by placing them in their own
kingdom, Monera. The prokaryotes are bacteria, including cyanobacteria, formerly called bluegreen algae. Organisms of the other four kingdoms all consist of cells organized on the
eukaryotic plan. The kingdoms Plantae, Animalia and Fungi are multicellular eukaryotes, each
kingdom defined by characteristics of structure and life cycle.
3. The six-kingdom alternative divides the prokaryotes into two kingdoms. This modification is
based on molecular evidence for an early evolutionary divergence between eubacteria (most
bacteria) and archaebacteria, and ancient lineage of prokaryotes with many unique
characteristics. Another set up is the three-domain system. It splits into Bacteria (eubacteria),
Archae (archaebacteria), and Eukarya (eukaryotes). This scheme assigns even more
significance to the ancient evolutionary split between eubacteria and archaebacteria by using a
super kingdom taxon called the domain. Finally, there is eight-kingdom system. This is one
example of the “kingdom-splitting” solution to the taxonomic problems posed by certain distinct
lineages of microorganisms. In addition to two separate prokaryotic kingdoms, this system also
splits the protests into three kingdoms.