Question

natural selection acted on the guppies. this kind of real - world manipulation of nature is called \experimental evolution,\ and it is growing increasingly popular among scientists working with organisms that reproduce quickly enough for humans to be able to see the outcome within our lifetimes. along with his students and colleagues, reznick removed groups of guppies from their predator - ridden lives below the waterfall and released them into previously guppy - free streams above the falls. although small predatory killifish occurred in these new sites, these fish do not pose anything close to the danger of the cichlids. then the scientists waited for nature to do its work, and they brought the descendants of the transplanted fish back to the lab to examine their reproduction. after just eleven years, the guppies released in the new streams had evolved to mature later, and have fewer, bigger offspring in each litter, just like the guppies that naturally occurred in the cichlid - free streams. other studies of guppies in trinidad have shown evolutionary change in as few as two and a half years, or a little over four generations, with more time required for genetic shifts in traits such as the ability to form schools and less time for changes in the colorful spots and stripes on a male’s body. figure 1 mean number of guppy offspring in high - and low - predation environments on north and south slopes of trinidad’s northern range mountains bar graph figure 2 mean embryo mass of guppy offspring in high - and low - predation environments on north and south slopes of trinidad’s northern range mountains bar graph figures adapted from david n. reznick, cameron k. ghalambor, and kevin crooks, “experimental studies of evolution in guppies: a model for understanding the evolutionary consequences of predator removal in natural communities.” ©2007 by blackwell publishing ltd. 21 the first paragraph mainly serves to a) establish the reason why a certain species was selected for scientific observation. b) illustrate the value of studying the offspring of a particular animal shortly after birth. c) introduce a theory at the center of an ongoing scientific debate. d) offer a rationale for the prevalence of a new field of scientific inquiry.

Explanation:

To solve this, we analyze each option:

• Option A: The first paragraph talks about "experimental evolution" and why guppies (a species) are used (they reproduce quickly so outcomes are seen in lifetimes). This matches establishing why the species was selected.
• Option B: The paragraph doesn't focus on studying offspring shortly after birth, so eliminate.
• Option C: There's no mention of an ongoing scientific debate, so eliminate.
• Option D: The paragraph introduces "experimental evolution" but doesn't offer a rationale for its prevalence as a new field; it explains why guppies are used for it. So eliminate.

Answer:

A) establish the reason why a certain species was selected for scientific observation.