#9 - Global surveys estimate the earth’s population of

[deck1134]

Hello PowerScore,

I am somewhat confused by answer D. Though I chose answer A, isn't it also true that if both the Male and Females fell by 2/3 in 15 years, then the species is in danger of extension? Is that not the same as answer choice A?

Thanks.

[Adam Tyson]

I think you might mean answer C, deck? The one about the numbers of male and female turtles? The reason that isn't a necessary assumption of this argument is that the argument is about percentages, not numbers, so an answer that is only about numbers cannot be correct.

Imagine this: The population of turtles years ago was 100 turtles. Of those, 75 were nesting females and 25 were all the others - 15 males of all sorts and 10 females that aren't nesting. Now, the nesting females dropped by two thirds, so that today there are only 25 of them. Did the author have to assume that the numbers of males and females are the same in order to conclude that the species is in danger of extinction? Not at all! In fact, in this particular case having an equal number of males and females would mean we had a GAIN of at least 10 males, maybe more if there are also some non-nesting females still around. That answer would actually hurt the conclusion, because the total population didn't suffer nearly as much of a loss as two-thirds.

Beware of answers about numbers when the question is about percentages, and vice versa!

[ROMI92]

Hi there,

Can someone please explain why answer choice A is correct?

[Adam Tyson]

Absolutely, ROMI92! The evidence in the stimulus is based on a survey of nesting females, but the conclusion is about the entire population of all leatherback turtles. What if the nesting females are not a representative sample of leatherback turtles generally? Could it be that the population of nesting females is down, but the overall population is holding steady, or even increasing? There might be plenty of males and plenty of females not currently nesting, and therefore the population might not be in any danger after all.

The assumption has to defend the argument against that possibility. The author has to believe that what is true of nesting females is true of the whole population. Otherwise, their argument makes no sense! That's what answer A is all about - confirming that the nesting females are a reliable measure of the overall population. They are a representative sample of the whole.