Natural selection is an immensely powerful yet beautifully simple theory that has held up remarkably well, under intense and unrelenting scrutiny and Line testing, for 135 years. In essence, natural selection locates the mechanism of evolutionary change in a "struggle" among organisms for reproductive success, leading to improved fit of populations to changing environments .. .

Yet powerful though the principle may 00) be ... natural selection is not fully sufficient to explain evolutionary change. First, many other causes are powerful, particularly at levels of biological organization both above and below the traditional Darwinian focus on organisms and their struggle for reproductive success. At the lowest level of substitution in individual base pairs of DNA, change is often effectively neutral and therefore random. At higher levels, involving entire species or faunas, punctuated equilibrium can produce evolutionary pm trends by selection of species based on their rates of origin and extirpation, whereas mass extinctions wipe out substantial parts of biotas for reasons unrelated to adaptive struggles of constituent species in "normal" times between such events.

Second ... no matter how adequate our general theory of evolutionary change, we also yearn to document and understand the actual pathway of life's history. Theory, of course, is relevant to explaining the pathway ... But the actual pathway is strongly underdetermined by our general theory of life's evolution. This point needs some belaboring ... Webs and chains of historical events are so intricate, so imbued with random and chaotic elements, so unrepeatable in encompassing such a multitude of unique (and uniquely interacting) objects, that standard models of simple prediction and replication do not apply.

History can be explained—with satisfying rigor if evidence be adequate—after a sequence of events unfolds, but it cannot be predicted with any precision beforehand . . . History includes too much chaos, or extremely sensitive dependence on minute and unmeasurable differences in initial conditions, leading to massively divergent outcomes based on tiny and unknowable disparities in starting points. And history includes too much contingency, or shaping of present results by long chains of unpredictable antecedent states, rather than immediate determination by timeless laws of nature.

Homo sapiens did not appear on the earth, just a geologic second ago, because evolutionary theory predicts such an outcome based on themes of progress and increasing neural complexity. Humans arose, rather, as a fortuitous and contingent outcome of thousands of linked events, any one of which could have occurred differently and sent history on an alternative pathway that would not have led to consciousness ..

Therefore, to understand the events and generalities of life's pathway, we must go beyond principles of evolutionary theory to a paleontological examination of the contingent pattern of life's history on our planet—the single actualized version among millions of plausible alternatives that happened not to occur. Such a view of life's history is highly contrary both to conventional deterministic models of Western science and to the deepest social traditions and psychological hopes of Western culture for a history culminating in humans as life's highest expression and intended POI planetary steward.

1. The primary purpose of the passage is to

A. suggest that the natural selection theory is no longer applicable to today's world
B. point out the limitations of natural selection at the lower and higher levels
C. propose changes to the natural selection theory to improve its accuracy
D. discuss the reasons why natural selection is not a complete evolutionary theory
E. expose problems with the natural selection theory in light of recent historical studies



2. Consider each of the choices separately and select all that apply.

In the first two paragraphs, the author implies that

A. there is strong reason to believe in the accuracy of Darwin's theory of evolutionary change
B. some biological changes are more complex than Darwin's theory allows for
C. biological changes are not necessarily the result of adverse conditions



3. Consider each of the choices separately and select all that apply.

The passage suggests that the author views the existence of human beings as

A. inevitable, although it may have come about in a different manner
B. a circumstance that began a brief time ago when compared to the existence of the earth itself
C. the result of a linear sequence of related events



4. The author mentions Homo sapiens primarily in order to

A. highlight the short period during which humans have lived on the earth
B. suggest the notion that the pathway to consciousness was a long-term process
C. support the idea that the pathway of life is determined, in large part, by random events
D. explain evolution through natural selection by employing a specific species as an example
E. emphasize the intricacy of events that leads to the evolution of an organism or species




5. Select the sentence that explains that the intermingling of highly detailed occurrences makes the prediction of evolution problematic.






6. Which of the following statements is supported by information given in the passage? cp

A. The study of history will never be completely satisfactory.
B. The theory of natural selection addresses the possibility of random events.
C. The evolution of life does not follow a fixed or determined path.
D. It is possible to determine with a fair degree of accuracy historical events.
E. Theories will always be inadequate because they are at best predictions.



7. Which of the following best describes the organization of the passage?

A. A theory is rejected, and new theories are suggested to replace it.
B. A theory is considered, and conditions are stated under which the theory can apply.
C. A theory is explained, and observations are made that both support and contradict it.
D. A theory is described, and its limitations are noted and then further explored.
E. A theory is outlined, and its relevance questioned by employing it in a different field of study.