1. How does the author of the article frame, or characterize, natural selection? A. The author characterizes natural selection as a mindless, violent animal.

B. The author personifies natural selection as a malicious killer, putting the evolutionary process in perspective by framing it with pre-meditated intent instead of natural biology and victims instead of prey.

C. The author exaggerates the process of natural selection, framing it in such a way to argue against the “survival of the fittest” mentality.

D. The author personifies natural selection as a malicious killer, suggesting that humanity, which is a link in the food chain, is as guilty as the evolutionary practice.

The kidney filters potentially toxic substances in the blood, and thus “clears” the blood of those substances. this clearance function is dependent upon and proportional to the diffusion gradient of the substance across filtering capillaries, i.e. if the concentration of the substance is doubled, twice as much will be cleared from each ml of blood that is filtered. suppose that the body produces a constant amount of a substance x per unit of time. the kidneys eliminate substance x at a rate directly proportional to the concentration of the substance and the volume of blood cleared each minute (c): elimination = c × [x], where [x] is the steady-state concentration of substance x. imagine an individual with an initial concentration of x equal to [x]0 who develops kidney disease. her baseline clearance c0 drops to one half of the original (½c0). what is the new steady state concentration of x? (for simplicity, assume that substance x is 100% filtered by the kidney).