Theory of Natural Selection

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0102 Darwinian Evolution

Paragraph 1

In 1859, British naturalist Charles Darwin published his now famous book “On Natural Selection”. In it he postulates that all life originates from a few progenitor organisms. Using the analogue of a tree, Darwin’s theory stated that all animals on earth had evolved from the same roots. Darwin formed these theories after five years travelling the world writing down observations, many of which were regarding the Galapagos Islands. Darwin’s conclusions were based on two ideas, firstly that there was descent through modification, and secondly that advantageous traits such as speed and strength made reproduction more likely, which in turn meant that these traits would be passed on to the next generation. Many of Darwin’s contemporaries were critical of his findings preferring the alternate theory of transmutation, where life forms generated spontaneously. Darwin could not explain why this happened—genetic research did not begin until the twentieth century; the process Darwin identified, however, began 3800 million years ago.

Paragraph 2

In the Precambrian Archaean Period (4 billion BCE to 2.5 billion BCE), scientists theorize that a lightning bolt reacted with water, methane, ammonia and hydrogen to create amino acids—the precursors for prokaryotes, which include a group of cells called cyanobacteria found in fossils. Prokaryotes are unicellular and comprise Archaea and Bacteria, which have a single strand of DNA. However, fossils show that during the Proterozoic Era (2.5 billion years BCE to 542 million years BCE) algae developed into multi-celled organisms called Eukaryotes. In 1981, biologist Lynn Margulis published the book “Symbiosis in Cell Evolution” to explain how Eukaryotes were derived from prokaryotes via endosymbiosis, whereby an oxygen-breathing bacteria took over an anaerobic bacteria and together were more efficient. Margulis proposed a modification to Darwin’s tree analogy that instead of separating into branches and twigs, organisms had symbiotic relations with branches rejoining to form new organisms that could not live separately. Much like Darwin she was ridiculed by the scientific community for her findings.

Paragraph 3

In 1987, Professor Kwang Jeon, conducted an experiment with a single celled amoeba, a large number of which became infected and died. Kwang monitored the remaining amoeba, which months later began to thrive. Kwang found that the bacteria were still present in the amoeba, but that when he attempted to cure them of the invaders, the amoeba could no longer survive independently. Thus provided further evidence that during the Precambrian Era, one prokaryotes engulfed another to form a Eukaryote process called endosymbiosis and confirming Margulis’s hypothesis. Further studies revealed that Eukaryote cells have tiny mitochondria, which look like a bacteria. The next step on the evolutionary journey came when Eukaryotes were invaded by chloroplasts, to form plants and fungi. These organisms spread rapidly in what is now known as the Cambrian explosion in 543 years ago. The first humans did not diverge from mammals until 85 million years ago, and the first human fossil was only discovered in Germany in 1857. Naturalists, however, thought that this strange human-like fossil was still just an extreme form of modern human, since there was no notion of other pre-human species, even though this skeleton had been found with animals long since extinct.

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[â- ] In 1937, Theodosius Dobzhansky’s book “Genetics and the Origin of the Species” explained the origin of species. Dobzhansky studied fruit flies and found that each fly was different. The life cycle of a fruit fly is ten days and they reproduce rapidly. He hypothesized that a species was a group of animals that reproduced with each other, that each fly had a set of genes unique to itself, but that new mutations occurred with each generation. [â- ] These gradual mutations made groups progressively more distinct. [â- ] In 1942, Mayr published a book “Systematics and the Origin of Species” following on from Dobzhansky’s work. Mayr postulated that many species were in fact similar; he found that the only way species differentiated was through geographic isolation. Moreover, that after a period of isolation, differences were too great to interbreed, even if the boundary no longer existed. Even with these findings, scientists still did not know how these divergences occurred. [â- ] A breakthrough did not come until 1953, when Francis Crick and James Watson used Rosalind Franklin’s precise molecular X-rays to identify the exact structure of DNA. Their findings showed how DNA replicated exact copies of itself with small mutations, and thus finally answered the mystery of how variations between generations occurred, and at the same time enabling scientists to identify similarities and differences not only between cells, but also between DNA and bases.

P1 - 1. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage?

Darwin’s conclusions were based on two ideas, firstly that offspring varied slightly from their parents, and secondly that advantageous traits such as speed and strength made reproduction more likely, which in turn meant that these traits would be passed on to the next generation.

Incorrect choices change the meaning in important ways or leave out essential information. <QT1.Sentence simplification>D

a. Darwin first thought that children were different from their parents, he next thought that only positive characteristics were passed on to future generations.

b. Combinations of inorganic material formed a living being by means unknown, and over time, further changes in structure and function that aided in survival remained.

c. Darwin was unsure how changed occurred but he was convinced it was based on two separate factors including parental traits and generational differences.

d. Darwin’s observations that offspring differed from parents and that advantageous characteristics were more likely to be passed on to future generations were the basis for his conclusions.

P1 - 2. The word <hl id=”reading-20”>”postulates”</hl> in the passage is closest in meaning to <QT3.vocab>A

a. theorizes

b. reports

c. discovers

d. produces

P1 - 3. According to paragraph 1, in what way did Darwin’s thinking change popular beliefs at the time of his publication?

<QT2. Fact> C

a. Darwin’s contemporaries immediately accepted his proposals as offering irrefutable proof of evolution.

b. Darwin’s findings were accepted by the scientific community, albeit reluctantly.

c. Darwin’s findings were rejected by the scientific community, which accepted the alternative theory of transmutation.

d. Darwin waited twenty years before publishing his findings for fear of being ridiculed by his peers.

Paragraph 6 is marked with an arrow <ar id=”reading-28”></ar>

P2 - 4. According to paragraph 2, which of the following is true of early cellular evolution?

<QT2.Fact> A

a. For the first 3 billion years of prokaryotic life, cell development progressed extremely slowly.

b. Proterozoic Era fossils show that prokaryotes evolved into eukaryotes when they combined with bacteria

c. Scientific experiments reproduced the process where eukaryotes engulfed prokaryotes

d. During the Archaean Era, bacteria and eukaryotes evolved at the same time to form prokaryotes

P2 - 5. According to paragraph 2, all of the following are true of the work conducted by Kwang and Margulis EXCEPT

<QT2. Negative fact>B

a. Kwang conducted research that supported theories originally produced by Margulis.

b. Margulis developed the first hypothesis about the origin of life on Earth.

c. Kwang’s experiment reached a conclusion different from the one he expected.

d. Kwang and Margulis’s work provided the basis for further studies about early life.

P2 - 6. Which of the following can be inferred from paragraph 2 about biologists’ discoveries related to the origin of life?

<QT6. inference>C

a. They were often incorrect and ridiculed by the entire scientific community for their incoherent findings.

b. They often carried out experiments without any basis in the real world.

c. They made their discoveries comparatively late compared to other scientific fields.

d. They conducted large amounts of research to ensure the accuracy of their findings thus delaying presentation of their conclusions.

P3 - 7. The word <hl id=”reading-22”>“engulfed”</hl> in the passage is closest in meaning to <QT3.vocab>C

a. flooded

b. created

c. absorbed

d. destroyed

P3 - 8. The word <hl id=”reading-20”>”diverge”</hl> in the passage is closest in meaning to <QT3.vocab>A

a. deviate

b. revert

c. adhere to

d. transgress from

P3 - 9. The word <hl id=”reading-25”>“unique to”</hl> in the passage is closest in meaning to <QT3. Vocab>B

a. common among

b. different from

c. natural to

d. limited to

P3 - 10. What purpose does paragraph 3 serve in the larger discussion of evolutionary biology?

<QT5.Rhetorical purpose>C

a. To explain the process through which speciation evolved on Earth during different evolutionary periods.

b. To demonstrate than an understanding of speciation can be applied to early evolutionary biology.

c. To show how discoveries in evolutionary biology are also symbiotic in nature.

d. To provide an example contradicting Darwin’s early observations and hypothesizing new ideas.

P4 - 11. Paragraph 4 suggests what about the speciation of the fruit fly?

<QT2. Fact>A

a. isolated groups of fruit flies form distinct species faster than groups without boundaries

b. fruit flies at a rate that makes speciation occur faster than in other species

c. all organisms can trace their adaptations back to the fruit fly

d. fruit flies share the same genes as eukaryotes and prokaryotes

P4 - 12. According to paragraph 4, how did Crick and Watson’s discovery change thinking about DNA and evolution?

<QT2. Fact>A

a. They identified the correct structure of DNA thereby demonstrating how DNA was able to replicate and mutate

b. They offered proof of transmutation and spontaneous generation of DNA mutations.

c. They discovered that DNA was not made of proteins, but amino acids.

d. They did not change prevailing thinking, merely offered confirmation for what was widely known.

P4 - 13. Look at the four squares <sq id=”reading-29”></sq> that indicate where the following sentence could be added to the passage. <QT7.insertion>2nd

Dobzhansky also found that larger populations diverged faster than smaller isolated populations; and isolated populations did not inherit the new mutations seen in other populations.

Where would the sentence best fit? Click on a square <sq id=”reading-29”></sq> to add the sentence to the passage.

14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Drag your answer choices to the spaces where they belong. To remove an answer choice, click on it. To review the passage, click VIEW TEXT.<Summary>BCF

Evolution is the process of organisms adapting to changes in their environment to survive and the death of those that do not.

Answer Choices

a. Initially, prokaryotes and eukaryotes existed in the oceans and absorbed bacteria, and through mutual adaptations in both organisms, caused increased diversity.

b. A single single-celled organism invaded another singles celled organism creating a eukaryote, which included parts of both cells and reproduced to form other eukaryotes.

c. After eukaryotes emerged, the Cambrian explosion saw an increased rate of evolution that led to land being colonized by plants and fungi, followed by other animals.

d. Organisms develop homogeneously, meaning that they share a set of common, homogenous genes which evolved differently over time in different animals.

e. Bacteria are the main cause of continued evolution in humans and other species because it is evolutionarily advantageous to use multiple cells.

f. The final pieces in the Darwinian puzzle were solved with the discovery of speciation and DNA, providing conclusive evidence that all life emerged from a single cell.

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