Biological Diversity

Paragraph 1

The human species came into being at the time of the greatest biological diversity in the history of the Earth. Today, as human populations expand and alter the natural environment, they are reducing biological diversity to its lowest level since the end of the Mesozoic era, 65 million years ago. The ultimate consequences of this biological collision are beyond calculation, but they are certain to be harmful. That, in essence, is the biodiversity crisis.

Paragraph 2

The history of global diversity can be summarized as follows: after the initial flowering of multicellular animals, there was a swift rise in the number of species in early Paleozoic times (between 600 and 430 million years ago), then plateaulike stagnation for the remaining 200 million years of the Paleozoic era, and finally a slow but steady climb through the Mesozoic and Cenozoic eras to diversity’s all-time high. This history suggests that biological diversity was hard won and a long time in coming. Furthermore, this pattern of increase was set back by five massive extinction episodes. The most recent of these, during the Cretaceous period, is by far the most famous, because it ended the age of the dinosaurs, conferred hegemony on the mammals, and ultimately made possible the ascendancy of the human species. But the Cretaceous crisis was minor compared with the Permian extinctions 240 million years ago, during which between 77 and 96 percent of marine animal species perished. It took 5 million years, well into Mesozoic times, for species diversity to begin a significant recovery.

Paragraph 3

Within the past 10,000 years biological diversity has entered a wholly new era. Human activity has had a devastating effect on species diversity, and the rate of human-induced extinctions is accelerating. Half of the bird species of Polynesia have been eliminated through hunting and the destruction of native forests. Hundreds of fish species endemic to Lake Victoria are now threatened with extinction following the careless introduction of one species of fish, the Nile perch. The list of such biogeographic disasters is extensive.

Paragraph 4

Because every species is unique and irreplaceable, the loss of biodiversity is the most profound process of environmental change. Its consequences are also the least predictable because the value of the Earth’s biota (the fauna and flora collectively) remains largely unstudied and unappreciated; unlike material and cultural wealth, which we understand because they are the substance of our everyday lives, biological wealth is usually taken for granted. This is a serious strategic error, one that will be increasingly regretted as time passes. The biota is not only part of a country’s heritage, the product of millions of years of evolution centered on that place; it is also a potential source for immense untapped material wealth in the form of food, medicine, and other commercially important substances.

Topic and Scope:

Species diversity; specifically, the history and consequences of species diversity.

 Purpose and Main Idea:

The author’s purpose is to trace the growth and decline of species diversity throughout history, as well as to argue that declining diversity is harmful to humanity. His specific main idea is that humanity will suffer serious, though unmeasurable, consequences if it doesn’t take measures to halt the current decline of species diversity.

Paragraph Structure:

Paragraph 1 introduces the author’s opinion about the current “biodiversity crisis.”

Paragraphs 2 and 3 provide historical background on the topic: paragraph 2 recounts the history of species diversity before the rise of humanity, while paragraph 3 discusses humanity’s negative effect on species diversity.

In paragraph 4, the author reiterates his earlier point that there’s no way to tell precisely what effects loss of species diversity will have, though it’s certain to be harmful. He goes on to note, however, that there are certain to be existential costs—the loss of the earth’s heritage—and more concrete costs in the area of food, medicine, and commercial products. The

Big Picture:

  • Note the classic structure of this very straightforward science passage. The author’s opinion appears in the first paragraph , and all of the subsequent paragraph s simply serve to justify and strengthen that opinion.
  • Whenever any author has a definite opinion about a topic, be sure that you’re clear about exactly what that opinion is—several of the questions are likely to test whether you’ve picked up on it.
  • This passage is an example of why it’s foolish to panic at the sight of a passage merely because it’s scientific in nature and seems to have a lot of “big words.” Sure, “biodiversity,” “multicellular animals,” not to mention the “Mesozoic, Paleozoic, Cenozoic,” eras may make the passage appear to be complex, but in fact, it’s really not. As noted above, the structure is clear, and the author’s opinion is crystal clear as well—these are the things that determine a passage’s difficulty level, and this passage, despite some scientific jargon, simply isn’t very difficult to understand.

CAT Verbal Online Course

Previous ArticleNext Article

CAT Online Course @ INR 13999 only