Critical Thinking Questions
- When the theory of evolution was first proposed, it met with a lot of criticism and disbelief, but it is widely supported today. Theories that have withstood a larger amount of criticism are more credible than those that are accepted easily
- The theory of evolution has its foundation in both biological and geological observations, making it a more credible theory because it can explain more about the world
- The theory of evolution relies on the heritability of traits, but the mechanism of this inheritance was not understood when the theory was developed. This reduces the credibility of the theory because the people who created it did not understand how it worked
- It is meaningful that two naturalists working independently from each other offered the same explanation for the same set of phenomena. When two people independently look at the same evidence and come to the same conclusion, this reinforces the credibility of that conclusion
- Natural selection produces beneficial adaptations, such as better running speed, in individuals that run more frequently
- Natural selection randomly mutates individuals’ genetic code until it produces beneficial adaptations, such as better running speed
- Natural selection produces adaptations, such as better running speed, to help individuals survive and reproduce
- Natural selection reproduces individuals with favorable genetic traits-such as the adaptation of better running speed-over time.
- An example of convergent evolution is the development of the same function, swimming, in organisms that live in different parts of the globe, such as Arctic beluga whales and Antarctic right whales. The fact that organisms that do not come in contact with each other have developed the same traits suggests that natural selection can produce similar adaptations in organisms who share a similar environment
- An example of convergent evolution is the set of adaptations, such as better running speed or more efficient hunting, developed by a species in response to competition with a new species that moves into the same region. The fact that a species adapts after it comes into contact with a competitor suggests that natural selection works more quickly with higher selective pressures.
- An example of convergent evolution is the development of an ancestral structure, a limb, into two different modern structures, such as a hand and a flipper. The fact that natural selection can cause a structure to develop down two different pathways due to different environmental conditions supports the theory of evolution
- An example of convergent evolution is the development of the same function, flying, in organisms that do not share a recent common ancestry, such as insects and birds. The fact that wings that allow flight have developed from very different original structures suggests that the process of natural selection can produce similar adaptations in two very different types of organisms who share a similar environment
- Vestigial structures are the result of convergent evolution, so they are good evidence that natural selection act similarly in similar environmental conditions.
- Vestigial structures are the result of common ancestry, so they are good evidence that different populations of organisms evolved from a common point.
- Vestigial structures are the result of convergent evolution, so they are good evidence for an end goal to evolution.
- Vestigial structures are the result of common ancestry, so they are good evidence for a common origin of all life.
How does the scientific meaning of theory differ from the common vernacular meaning?
- A scientific theory is a hypothesis that needs to be tested, whereas people often use theory to mean a simple guess.
- A scientific theory is a statement that has been proven correct, while people often use it to mean a statement that has not yet been verified.
- A scientific theory is a thoroughly tested set of explanations for a body of observations of nature, while people often use it to mean a guess or speculation.
- A scientific theory is a random guess, while people often use it to mean a statement that is somewhat based in fact.
Reproduction occurs when a gamete fertilizes another gamete. This occurs through a number of mechanisms. In fish, sperm and ova are released directly into the water. The sperm can swim to fertilize the ova. Explain what evolutionary adaptations are needed for fertilization to occur in terrestrial flowers, mentioning both the roles of the gametophytes and the roles of the gametes.
Sickle cell anemia is caused by a mutation in the gene for hemoglobin, which follows a Mendelian inheritance pattern. To have sickle cell anemia, an individual must inherit two copies of this mutation. However, having only one copy of the mutation provides malaria resistance. Predict how this mutation would affect the reproductive potential of humans in countries with endemic malaria.
Why is having a way of defining species and distinguishing between them important for the study of evolution?
- A distinction between species allows scientists to understand the common origin of all species.
- A common definition of species allows scientists to agree on all aspects of the theory of evolution.
- Divergence can only occur at the species level: It does not occur to larger taxa. Therefore it is important to know which groups are distinct species.
- In the study of evolution, the species is the unit over which change is measured.
If a population stopped reproducing sexually, but still reproduced asexually, how would its genetic variation be affected over time? Could speciation occur in this situation?
- Genetic variation would increase and speciation would be possible
- Genetic variation would increase and speciation would not be possible.
- Genetic variation would decrease and speciation would be possible.
- Genetic variation would decrease and speciation would not be possible.
What role do prezygotic and postzygotic barriers play in speciation?
- Prezygotic and postzygotic barriers allow for the formation of less-fit hybrids that reinforces speciation.
- Prezygotic and postzygotic barriers prevent interbreeding of species such that there is no gene flow between them.
- Prezygotic and postzygotic barriers prevent migration of the two species, causing them to remain in contact with each other and begin to interbreed.
- Prezygotic and postzygotic barriers are present only in newly formed species, allowing scientists to identify the time of divergence of the species.
- Allopatric speciation is more common because it prevents gene flow between the species.
- Allopatric speciation is more common because it involves stronger prezygotic barriers.
- Sympatric speciation is more common because it prevents gene flow between the species.
- Sympatric speciation is more common because it involves stronger prezygotic barriers.
- The finches likely shared a common ancestor when they came to the island, but exhibited different traits. Each species of finch settled the island where its particular traits would be the most adaptive.
- The finches likely originated as one parent species, but over time mutations caused them to develop reproductive barriers and separate into different species. To reduce competition, the species then radiated out to inhabit different islands.
- The finches likely dispersed from one parent species, and natural selection based on different food sources in differing habitats led to adaptive changes, evidenced in the different beak shapes of the different species-each suited to a different food type.
- It is likely that a series of cataclysmic events caused an original finch species to diverge into the many finch species that inhabited the islands when Darwin observed them. The different species then radiated out to the different islands and adapted to the different conditions on each.
A population of flowers was separated into two when a new river cut through the plain in which they were growing. The number of interbreeding events per year for the two groups of flowers is shown in the graph below. Twenty-four years after the new river, can you conclude that the two populations of flowers have become new species? Why or why not?
- Separate species cannot interbreed, so hybrid reproduction does not occur in nature
- If the hybrid offspring are more fit than the parents, reproduction would likely continue between both species and the hybrids, eventually bringing all organisms under the umbrella of one species
- Two species that have recently diverged from each other can reproduce with each other, creating hybrid individuals that belong to the species of the parents’ common ancestor.
- If two species occupy the same niche in the same area, they can either compete or they can collaborate and reproduce with each other, eventually fusing into a single species
- Both models ignore the influence of gene flow for simplicity’s sake.
- Both models apply only to island chains.
- Both models require the influence of cataclysmic events which precipitate rapid adaptation and speciation
- Both models conform to the rules of natural selection and the influences of gene flow, genetic drift, and mutation
Describe a situation where hybrid reproduction would cause two species to continue divergence.
- If two closely related species continue to produce hybrids, the hybrids will compete with both species, causing them to find new niches which will further their divergence
- If two closely related species continue to produce hybrids, they will develop reproductive barriers to prevent production of hybrids, to ensure that they remain separate species.
- If two closely related species continue to produce hybrids that are less fit than the parent species, there would be reinforcement of divergence.
- If two closely related species continue to produce hybrids they will always converge into a single species