Q22 - A tiny, tree living thirps

[ChineseCaveMan]

Hello all, here is my explanation.

This is an inference question, as indicated by the stem saying "properly inferred". Hence, we can be sure we have to stick pretty close to the stimulus.

A few statements are made. Here they are in sum:

1. Thirps will either
(a) - lay eggs
or
(b) - have Live young

2. Further, the Eggs will be female, while the live young will be Male.

3. lastly, in any brood, there will be less males than females.

On a question like this, I expect the answer to be a combination of multiple statements. As correct Answer choice (C) turns out, it combines all three. If more eggs survive than live broods, & the eggs are females, (the others being males), then it can be deduced that more thirps are born successfully by eggs, than live - born males.


For the other incorrect answers:

(A) - The only species? where does it say that? scribble this answer out!

(B) - Completely unsupported. Also, 'any' is too strong. this type of language is not matched by the stimulus.

(D) - Cannot be inferred. We are not given enough information.

(E) - We know nothing about this.

HTHH

[maryadkins]

Thank you for sharing your explanation!

You're correct. My only additional comment on (C), to clarify, is that part of the reason we know this is because by adulthood we have even numbers of males and females, and more males survive to adulthood. So females must have more of an advantage at the get-go, i.e. when they're born.

[kyuya]

First off, "thrips" sound disturbing.

Anyway, into the question.

We learn three key facts about thrips:

1.) If hatched from egg --->female, If live born ---> male.

2.) If live born brood --> produces less than eggs, If a brood of eggs ----> More than live borns

3.) Then, a much larger proportion of male offspring than female offspring survives to adulthood, and among thrips reaching adulthood the ratio of females to males is about even.

So females off spring (which are produced by eggs) produce MORE than male off springs (produced by live birth), but they end up being about the same. What does this tell us? More off spring in this species are born through eggs than are born through live birth, but they also do not survive as well as their male counterparts.

I'll start with the wrong.

(A) It is the ONLY species? We don't know this. It is the only as of right now, but only is a strong word. We may discover another freak species like this one that can do both, so we cannot make such a strong claim as (A) would like us to.

(B) The latter part of this AC is where an issue happens. "can also reproduce by bearing live young but not necessarily vice versa". It is suggesting a limitation that we do not know anything about. We only know that through any given INSTANCE of reproduction they may only use live birth OR egg and not both. This is the only limitation we know of.

(D) We don't know this. All we know is that females and males reach adulthood at approximately the same ratio. Its possible that due to eggs producing way more, they do not need to produce at roughly the same rate in terms of instances of live and egg births. I think this answer choice is hoping you conflate instances of live births and egg births with the rate at which males and females appear.

(E) We don't know this. They may ALL use both of the methods. Once again, this answer choice I believe is hoping you confuse the fact that during one instance of reproduction they can only either use live or egg birth, however, throughout their lifetime its possible that this species may rotate using one brood as live births and another brood as eggs. To be clear, one instance of birth means that either the entire brood is egg, or the entire brood is live birth. There is never going to be a brood where some are birthed live ,and other are eggs. NO MIXING!

Okay, so onto the right answer..

(C) If males live at a higher rate proportionally (and they are born through live birth) than females (egg birth), that must mean that there are more egg births. There is also the premise that tells us during egg births, more offspring are born in comparison to live broods.

[XbdD569]

I have a question regarding D. I interpret D as "instances of live-born broods are the same as broods hatched from eggs over time". We know all live-born are males, all hatched from eggs are female, and the ratio of male to female is even reaching adulthood (over time). Then D should be right?

Thanks!!!

[ohthatpatrick]

D would be wrong because of two of the other facts we've heard.

There are more men born per brood from live born than woman per brood from eggs.

Say you get 6 men per live born brood
and
4 women per egg brood.

If we had 60 men and 60 women as adults, that means there would have been 10 instances of live born and 15 instances of women.

The other thing that messes up your math is that males are more likely to reach adulthood than females.

So if there's an equal number of adult males/females, then we must have started with more females.

If we had an equal number of male/female babies, and males are way more likely to reach adulthood, then we would end up with more male adults than female adults.

[WesleyC316]

Is it enough to infer answer choice C based just on the last sentence? Larger proportion of male surviving, but ended up being equal in number to female thrips. I think that alone tells me that there are more females to begin with. Am I missing something?