Chapter 11 Glossary, Summary, and Practice Questions
KEY TERMS
adaptation a heritable trait or behavior in an organism that aids in its survival in its present environment
adaptive radiation a speciation when one species radiates out to form several other species
allopatric speciation a speciation that occurs via a geographic separation
analogous structure a structure that is similar because of evolution in response to similar selection pressures resulting in convergent evolution, not similar because of descent from a common ancestor
bottleneck effect the magnification of genetic drift as a result of natural events or catastrophes
convergent evolution an evolution that results in similar forms on different species
dispersal an allopatric speciation that occurs when a few members of a species move to a new geographical area
divergent evolution an evolution that results in different forms in two species with a common ancestor
founder effect a magnification of genetic drift in a small population that migrates away from a large parent population carrying with it an unrepresentative set of alleles
gene flow the flow of alleles in and out of a population due to the migration of individuals or gametes
gene pool all of the alleles carried by all of the individuals in the population
genetic drift the effect of chance on a population’s gene pool
homologous structure a structure that is similar because of descent from a common ancestor
inheritance of acquired characteristics a phrase that describes the mechanism of evolution proposed by Lamarck in
which traits acquired by individuals through use or disuse could be passed on to their offspring thus leading to evolutionary change in the population
macroevolution a broader scale of evolutionary changes seen over paleontological time
microevolution the changes in a population’s genetic structure (i.e., allele frequency)
migration the movement of individuals of a population to a new location; in population genetics it refers to the movement of individuals and their alleles from one population to another, potentially changing allele frequencies in both the old and the new population
modern synthesis the overarching evolutionary paradigm that took shape by the 1940s and is generally accepted today
natural selection the greater relative survival and reproduction of individuals in a population that have favorable heritable traits, leading to evolutionary change
population genetics the study of how selective forces change the allele frequencies in a population over time
speciation a formation of a new species
sympatric speciation a speciation that occurs in the same geographic space
variation the variety of alleles in a population
vestigial structure a physical structure present in an organism but that has no apparent function and appears to be from a functional structure in a distant ancestor
vicariance an allopatric speciation that occurs when something in the environment separates organisms of the same species into separate groups
CHAPTER SUMMARY
Discovering How Populations Change
Evolution by natural selection arises from three conditions: individuals within a species vary, some of those variations are heritable, and organisms have more offspring than resources can support. The consequence is that individuals with relatively advantageous variations will be more likely to survive and have higher reproductive rates than those individuals with different traits. The advantageous traits will be passed on to offspring in greater proportion. Thus, the trait will have higher representation in the next and subsequent generations leading to genetic change in the population.
The modern synthesis of evolutionary theory grew out of the reconciliation of Darwin’s, Wallace’s, and Mendel’s thoughts on evolution and heredity. Population genetics is a theoretical framework for describing evolutionary change in populations through the change in allele frequencies. Population genetics defines evolution as a change in allele frequency over generations. In the absence of evolutionary forces allele frequencies will not change in a population; this is known as Hardy-Weinberg equilibrium principle. However, in all populations, mutation, natural selection, genetic drift, and migration act to change allele frequencies.
Mechanisms of Evolution
There are four factors that can change the allele frequencies of a population. Natural selection works by selecting for alleles that confer beneficial traits or behaviors, while selecting against those for deleterious qualities. Mutations introduce new alleles into a population. Genetic drift stems from the chance occurrence that some individuals have more offspring than others and results in changes in allele frequencies that are random in direction. When individuals leave or join the population, allele frequencies can change as a result of gene flow.
Evidence of Evolution
The evidence for evolution is found at all levels of organization in living things and in the extinct species we know about through fossils. Fossils provide evidence for the evolutionary change through now extinct forms that led to modern species. For example, there is a rich fossil record that shows the evolutionary transitions from horse ancestors to modern horses that document intermediate forms and a gradual adaptation o changing ecosystems. The anatomy of species and the embryological development of that anatomy reveal common structures in divergent lineages that have been modified over time by evolution. The geographical distribution of living species reflects the origins of species in particular geographic locations and the history of continental movements. The structures of molecules, like anatomical structures, reflect the relationships of living species and match patterns of similarity expected from descent with modification.
Speciation
Speciation occurs along two main pathways: geographic separation (allopatric speciation) and through mechanisms that occur within a shared habitat (sympatric speciation). Both pathways force reproductive isolation between populations. Sympatric speciation can occur through errors in meiosis that form gametes with extra chromosomes, called polyploidy. Autopolyploidy occurs within a single species, whereas allopolyploidy occurs because of a mating between closely related species. Once the populations are isolated, evolutionary divergence can take place leading to the evolution of reproductive isolating traits that prevent interbreeding should the two populations come together again. The reduced viability of hybrid offspring after a period of isolation is expected to select for stronger inherent isolating mechanisms.
Common Misconceptions about Evolution
The theory of evolution is a difficult concept and misconceptions abound. The factual nature of evolution is often challenged by wrongly associating the scientific meaning of a theory with the vernacular meaning. Evolution is sometimes mistakenly interpreted to mean that individuals evolve, when in fact only populations can evolve as their gene frequencies change over time. Evolution is often assumed to explain the origin of life, which it does not speak to. It is often spoken in goal-directed terms by which organisms change through intention, and selection operates on mutations present in a population that have not arisen in response to a particular environmental stress. Evolution is often characterized as being controversial among scientists; however, it is accepted by the vast majority of working scientists. Critics of evolution often argue that alternative theories to evolution should be taught in public schools; however, there are no viable alternative scientific theories to evolution. The alternative religious beliefs should not be taught as science because it cannot be proven, and in the United States it is unconstitutional. Science is silent on the question of the existence of a god while scientists are able to reconcile religious belief and scientific knowledge.
ART CONNECTION QUESTIONS
- Figure 11.7 Do you think genetic drift would happen more quickly on an island or on the mainland?
REVIEW QUESTIONS
- Which scientific concept did Charles Darwin and Alfred Wallace independently discover?
- mutation
- natural selection
- overbreeding
- sexual reproduction
- Which of the following situations will lead to natural selection?
- The seeds of two plants land near each other and one grows larger than the other.
- Two types of fish eat the same kind of food, and one is better able to gather food than the other.
- Male lions compete for the right to mate with females, with only one possible winner.
- all of the above
- What is the difference between micro- and macroevolution?
- Microevolution describes the evolution of small organisms, such as insects, while macroevolution describes the evolution of large organisms, like people and elephants.
- Microevolution describes the evolution of microscopic entities, such as molecules and proteins, while macroevolution describes the evolution of whole organisms.
- Microevolution describes the evolution of populations, while macroevolution describes the emergence of new species over long periods of time.
- Microevolution describes the evolution of organisms over their lifetimes, while macroevolution describes the evolution of organisms over multiple generations.
- Population genetics is the study of .
- how allele frequencies in a population change over time
- populations of cells in an individual
- the rate of population growth
- how genes affect embryological development
- Galápagos medium ground finches are found on Santa Cruz and San Cristóbal islands, which are separated by about 100 km of ocean. Occasionally, individuals from either island fly to the other island to stay. This can alter the allele frequencies of the population through which of the following mechanisms?
- natural selection
- genetic drift
- gene flow
- mutation
- In which of the following pairs do both evolutionary processes introduce new genetic variation into a population?
- natural selection and genetic drift
- mutation and gene flow
- natural selection and gene flow
- gene flow and genetic drift
- The wing of a bird and the arm of a human are examples of .
- vestigial structures
- molecular structures
- homologous structures
- analogous structures
- The fact that DNA sequences are more similar in more closely related organisms is evidence of what?
- optimal design in organisms
- adaptation
- mutation
- descent with modification
- Which situation would most likely lead to allopatric speciation?
- A flood causes the formation of a new lake.
- A storm causes several large trees to fall down.
- A mutation causes a new trait to develop.
- An injury causes an organism to seek out a new food source.
- What is the main difference between dispersal and vicariance?
- One leads to allopatric speciation, whereas the other leads to sympatric speciation.
- One involves the movement of the organism, whereas the other involves a change in the environment.
- One depends on a genetic mutation occurring, whereas the other does not.
- One involves closely related organisms, whereas the other involves only individuals of the same species.
- Which variable increases the likelihood of allopatric speciation taking place more quickly?
- lower rate of mutation
- longer distance between divided groups
- increased instances of hybrid formation
- equivalent numbers of individuals in each population
- The word “theory” in theory of evolution is best replaced by .
- fact
- hypothesis
- idea
- alternate explanation
- Why are alternative scientific theories to evolution not taught in public school?
- more theories would confuse students
CRITICAL THINKING QUESTIONS
- If a person scatters a handful of plant seeds from one species in an area, how would natural selection work in this situation?
- Explain the Hardy-Weinberg principle of equilibrium.
- Describe natural selection and give an example of natural selection at work in a population.
- Why do scientists consider vestigial structures evidence for evolution?
- Why do island chains provide ideal conditions for adaptive radiation to occur?
there are no viable scientific alternatives- it is against the law
- alternative scientific theories are suppressed by the science establishment
- Two species of fish had recently undergone sympatric speciation. The males of each species had a different coloring through which females could identify and choose a partner from her own species. After some time, pollution made the lake so cloudy it was hard for females to distinguish colors. What might take place in this situation?
- How does the scientific meaning of “theory” differ from the common, everyday meaning of the word?
- Explain why the statement that a monkey is more evolved than a mouse is incorrect.
