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EVOLUTION QUESTIONS ANSWER KEY
Answer the following questions in complete sentences. Your answer should be in your own words and should be complete thoughts, however may use your notes and textbook. 1.
Charles Darwin proposed that evolution by natural selection was the basis for the differences that he saw in similar organisms as he traveled and collected specimens in South America and on the Galapagos Islands. Explain 4 to 6 components included in the theory of evolution by natural selection as presented by Darwin. (remember that Darwin did not know about DNA or other molecular evidence)
Within this answer you could explain 4 of the following: 1. 2. 3. 4.
5. 6. 7.
NATURAL VARIATION- “Each individual is unique” ADAPTATION-characteristic that helps an organism be more suited to its environment/survive and reproduce OVERPRODUCTION of offspring results in more offspring than can survive STRUGGLE FOR EXISTANCE-Organisms must compete for food, space, mates NATURAL SELECTION also called “SURVIVAL OF FITTEST” i. Individuals that are best adapted to their environment will survive and reproduce ii. Inherited favorable characteristics become more common from one generation to the next FITNESS = measure of organism's reproductive success (greater number of offspring that carry your genes) DESCENT WITH MODIFICATION-organisms have descended from a common ancestor; EXTINCTION occurs when previous adaptations are no longer suitable to a changed environment
You cannot earn credit for mentioning genetics or genes. Darwin did not know about genes. 2.
Evolution by natural selection has been able to explain both the unity and diversity of life on Earth. Discuss how natural selection explains the following phenomenon and cite an example for each: a.
Mimicry - Population 1 has an adaptation that enables individuals to survive and reproduce - Population 2 originally contained variations that included some similarity to Population 1. This served as an adaptation & these individuals were afforded the same advantage as those in Population 1. Mimics are therefore selected for and are able to survive and reproduce more passing on the trait - Example: warning coloration of monarch butterflies or poisonous snakes
b.
Convergent evolution - “similar solutions to similar problems”: analogous structures - similar adaptations that enable unrelated organisms to be successful but are not due to a recent common ancestor
- Example: wings on birds, insects, bats 3.
Compare and contrast artificial selection and natural selection. Explain how artificial selection was useful to Darwin in his thinking about evolution.
- artificial selection is human-created evolution; intentional selection: humans are the selection agent: they select the traits in a species that they want to propagate; humans choose the matings and therefore determine which individuals are successful. artificial selection does not produce individuals that are adapted to the environment, but rather adapted to human use. - natural selection is based environmental selection factors. Adaptations bring about successful in a natural setting. - both exert a selection pressure on a species. - artificial selection enabled Darwin to see that traits are passed from parent to offspring & that traits could accumulate in a population if individuals bearing those traits are allowed to reproduce selectively.
4.
In terms of climate and geology, Charles Darwin noted that Galapagos Islands are nearly identical to the Canary Islands. Darwin was struck, however, by the fact that the Canary Islands, just off the coast of Africa (200km or 120 miles), contain very few unique species. Whereas the Galapagos Islands, over 800km (~500 miles) off the coast of South America, are home to scores of unique species, found nowhere else in the world. Give an evolutionary explanation for why remote islands would give rise to unique species, while those relatively close to mainland contain few if any species not found on the mainland. - remote islands are isolated - strong selection pressure to adapt to the environment or not survive. - adaptive radiation colonizing new habitats - founder effect & genetic drift (reduction of variation due to small population); no gene flow - geographic isolation - nearby islands share migration with mainland
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AP Biology
- gene flow (movement in and out): migration may mean island population & mainland share gene pool - may have similar selective pressures as mainland - similar habitats on mainland & island will be populated by same species so they will experience similar selective pressures therefore few opportunities for the evolution of new or distinct species 5.
Explain how the fossil record supports the principle of evolution by natural selection.
- many extinct species resemble modern species but have slight differences in traits - fossils show change over time - modern species have survived due to variations in traits – adaptations -- that allowed them to be more competitive 6.
Much of the power of the theory evolution is its ability to provide a sensible framework for understanding the diversity of life. a.
The illustration below shows the forelimbs of a variety of mammals as homologous structures. What are homologous structures and explain how this serves as evidence for evolution by natural selection. These are homologous traits with same bones in each structure even though they serve different functions Differences in the structures are evidence of adaptation to different environments Similarities in the structures are evidence of common ancestry
b.
The illustration below shows the skeleton of a whale and highlights a structure that can be classified as a vestigial structure. What is a vestigial structure and explain how the highlighted structure serves as evidence for evolution by natural selection. A vestigial structure is one that is present but has no function. The highlighted structure are remnants of pelvic bones. Pelvic bones are only necessary for animals that have legs. Presence of this structure is evidence that whales descended from land mammals.
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AP Biology
Although individuals who are homozygous for the sickle-cell allele (HsHs) often die at a young age, the sickle-cell allele (Hs) is common in populations living in areas where malaria is prevalent. a.
Briefly explain why the sickle-cell allele (Hs) is so common in regions where malaria is found. It is called heterozygote advantage - individuals homozygous normal (HbHb) are more susceptible to dying from malaria - individuals homozygous sickle-cell (HsHs) are more susceptible to dying from sickle cell disease - heterozygotes: malaria parasite is killed when cells sickle, so heterozygotes are less susceptible to malaria and do not have as crippling a case of sickle cell disease
8.
The manes of male lions as an example of sexual selection. Female lions tend to chose males with large, dark manes as mates. a.
Why are such manes considered examples of sexual selection rather than examples of other forms of natural selection? Be brief but specific. - manes don’t benefit the males directly; don’t help them hunt, survive, etc. - a mane is, in fact, uncomfortable to the individual possessing it - its main role is to promote reproductive success: finding a mate - doesn’t help individual survive; helps individual reproduce
b.
Male lions who do not inherit genes that help them to produce large, dark manes are less likely to breed. Explain the benefits to a female lion who instinctively selects a mate with a large dark mane. - Females pick mates on an instinctive preference, NO CREDIT for female “wants” to find a fit male or female “wants” to provide for her offspring, or female sees dark mane and “knows” the male has high testosterone level. If this instinctive preference has the female choosing a mate with large dark mane, she will automatically be choosing a fit mate, with a high testosterone level and probably with a high sperm count. That instinctive behavior will be rewarded with lots of offspring (because of high sperm count) and pretty good protection because the male is pretty fit. For females who instinctively choose males with small light manes that behavior will be penalized with higher mortality rates in cubs (from less fit male) and fewer offspring (from a male with a lower sperm count).
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AP Biology
Molecular biology (DNA , RNA, Protein) has given us the tools to test evolutionary theory beyond what could even be imagined in Darwin’s day. Describe examples of evidence which molecular biology has discovered that supports the understanding that clusters of species share a recent common ancestor. - similar sequences in genes or proteins are found in closely related species - we assume that DNA changes (mutation) at a constant rate - the more similar the sequence the more closely related. - Example: compare amino acid sequence of hemoglobin in vertebrates or Cytochrome C across a broad array of species
10. Are natural populations ever in Hardy-Weinberg equilibrium? List and explain each of the assumptions of Hardy-Weinberg equilibrium. No, natural populations are rarely (never?) in H-W equilibrium.
A.
no selection - the environment exerts a selective force (predators, parasite, disease, competition)
B.
no mutation- errors in replication happen at a constant rate
C.
random mating - sexual selection exists
D.
no gene flow - immigration & emigration usually happens
E.
infinitely large populations - no such thing…population growth is finite
