Chapter 22 Practice Problems / Case Study Problems Flashcards
Why was the age of the Earth so important for Darwin’s ideas about evolution?
James Hutton and Charles Lyell proposed that geologic events/features occur via gradual mechanisms over long periods of time, and that these mechanisms are still operating to this day. This would suggest that the Earth is much older than a few thousand years old. These ideas also introduced the idea that small, incremental changes can accumulate and ultimately produce the profound changes in species found in the fossil record.
The age of the Earth was very important to Darwin, because if it wasn’t as old as he thought, he couldn’t conceive the possibility that these changes (descent with modification) would have any time to occur.
How does the concept of descent with modification explain both the unity and diversity of life?
Organisms share characteristics (unity of life) because they share common ancestors; the great diversity of life occurs because new species have repeatedly formed when descendant organisms gradually adapted to different environments, thereby becoming different from their ancestors.
What if you discovered a fossil of an extinct mammal that lived high in the Andes, would you predict that it would be more closely resembling present-day mammals from the South American rainforest or present-day mammals that live high in Asian mountains? Explain.
Because the fossilized, extinct mammal (or its ancestors) colonized the mountains from parts of South America, it is more likely that the fossilized mammal would resemble the present-day mammals from the South American rainforest given that they have a more recent common ancestor. However, it is possible (and somewhat likely) that the fossilized extinct mammal could resemble the Asian mammals in the mountains due to convergent evolution that is not determined by ancestral lineage.
How is evolution supported by scientific evidence?
Direct observations: In cases like the soapberry bug, where their beak length fluctuates depending on the depth of the seed of the fruit in which they feed on. Another observation is drug-resistant pathogens that adapt to exposure to antibiotics due to genetic variation present in their populations, and thus drug resistant offspring are allowed to survive and reproduce.
Homology: Different organisms have characteristics that have underlying similarity, yet function differently. These different characteristics have been observed in nature. In the forelimbs of mammals, the bone structure and arrangement have close similarities amongst each other, but have different functions. Vestigial structures like pelvic bone vestiges in snakes and all vertebrates having a tail , pharyngeal (throat) arches as well.
The Fossil Record: shows that present-day organisms differ from past organisms, and that many species go extinct. They also show evolutionary changes that have occurred in organisms as well. Fossils also shed light on the origins of new groups of organisms - as they can map DNA sequence similarities and show how animal structures transitioned into new structures with similarities to the old.
Biogeography - the study of geographic distribution of species. Continental drift and Pangea also allow us to predict where fossils of different groups of organisms might be found. It also explains the mystery of species related to a common ancestor that are scattered across the world in varied locations, as those species were not diverged during the age of Pangea, and thus their ancestor was able to roam to different areas within the interconnected continent.
Describe how overreproduction and heritable variation relate to evolution by natural selection
All species have the potential (and tendency) to overreproduce (to produce more offspring than can be supported by the environment). This causes Darwin’s phenomenon of the “struggle for existence” where weaker offspring are eaten, starved, diseased, etc and die off, while other members of the population inherit better traits that allow them to survive. Since a population will obtain a wide range of heritable variation, and that “the more the merrier” applies to genetic variation, natural selection will select for more advantageous traits and will allow for those offspring to survive and reproduce at higher rates.
Explain why the following statement is inaccurate: “Antibiotics have created drug resistance in MRSA”.
The resistance arose due to a mutation during DNA replication prior to binary fission at complete random chance. Since the population of bacteria had a wide range of genetic variation (including this resistance gene that arose), the gene was selected naturally by the environment. The mutations happen at random and are not caused by the environment.
DDT is a synthetic pesticide that was developed in the 1940s and was widely used to control mosquito populations in areas with malaria. Mosquitos resistant to the pesticide DDT first appeared in India in 1959, but now are found throughout the world. Suggest an explanation for the global spread of DDT resistance both in the 1960s and now.
The rapid rise of DDT resistance in India was more than likely due to genetic variation (and a random mutation that coded for resistance) and subsequent natural selection of the mutation that codes for resistance to the DDT pesticide. This resistance spread across the world by migration, human transportation, winds, etc. and thus the resistance would proliferate there too if DDT is being used.
How does evolution account for (a) the similar mammalian forelimbs with different functions (figure 22.15 homologous structures) and (b) the similar forms of the two distantly related mammals in figure 22.18 (convergent evolution).
a) despite their different functions, these forelimbs resemble each other loosely as they were all inherited from a common ancestor (homologous structures)
b) the similar features in this case are not from ancestral lineage, but from convergent evolution, where species adapt to similar surroundings but are not ancestrally related.
What if fossils show that dinosaurs originated 200-250 mya. Would you expect the geographic distribution of early dinosaur fossils to be broad (on many continents) or narrow (on one or a few continents only)? Explain.
The dinosaurs would have broad distribution, because they existed around the time of Pangea (before the continents separated, 200-250 Mya). Because dinosaurs are large and mobile, they would have been physically able to move to all corners of Pangea, and thus would be widely distributed after the continental divide.
Summarize the different lines of evidence supporting the hypothesis that cetaceans descended from land mammals and are closely related to even-toed ungulates.
- Fossils document that early cetaceans had hind limbs (as expected for organisms that descended from a land mammal; these fossils also show that cetacean hind limbs became reduced over time
- Other fossils show that early cetaceans had an ankle bone that is only similarly compared to those of even-toed ungulates
- DNA sequence data also indicates that even-toed ungulates are closely related to cetaceans.
Review the process of natural selection. Use the steps to explain how PCB resistance became so common among tomcod in the Hudson. Be sure to include mutation, fitness, selective pressure, and adaptation in your explanation.
- Genetic variation within tomcod population - many fish have normal alleles without the AHR receptor gene that resists PCB.
- Differential reproduction - the environment of the Hudson does not produce unlimited population growth because it selectively pressures fish without the AHR gene due to the presence of PCB toxin. Tomcods with mutated gene have no problem existing in the environment, while tomcods without the gene struggle to survive/reproduce.
- Heredity - Since the tomcod with the AHR gene are the ones who survived, they are left to reproduce and produce offspring with the mutated AHR gene. Tomcod that are resistant to PCB now make up a majority of the population in the Hudson.
In this blog post, the author describes the tomcod as “a quick learner” because of the population’s adaptation to PCB’s. Is “learning” an accurate way to describe the change in the Hudson River tomcod population? Why or why not?
Learning is not an accurate way to describe this change because it implies that the Tomcod themselves adapted to their surroundings. They merely benefited from genetic variation in their population that allowed for an AHR gene mutation to occur, and natural selection chose this gene.
The data shown on the map above support the hypothesis that natural selection for PCB resistance has occurred among tomcod in the Hudson. What sort of evidence regarding gene frequencies in different populations would argue against this hypothesis (i.e., imagine what the scientists would have observed in this study if natural selection on the AHR gene had not occurred among Hudson River tomcod)?
Evidence that there were substantial populations of tomcod that held the AHR gene without prolonged exposure (selective pressure) to the PCB toxin would suggest that natural selection did not occur.
Also, if no tomcod survived in the Hudson due to the presence of PCB, this would be an indication that natural selection did not occur.
- Why is it not accurate to assume that species that feed on tomcod will also evolve resistance to PCBs. What misconception about the process of evolution by natural selection is highlighted under the thinking that natural selection “provides organisms with the traits they ‘need’ to survive”? Be sure to explain why this misconception is incorrect using what you know about how natural selection operates.
If natural selection gave organisms what they “need” to survive, the process would not be random. It only can select traits that are already available in a population.
Species that feed on tomcod will most likely not evolve resistance to PCBs because the exposure to the toxin is not consistent or intense enough to cause natural selection to select for a mutation of PCB resistance. There simply isn’t enough selective pressure to set natural selection in motion. Also, it is not a guarantee that other mutations will arise in other species to resist PCB.
