20. Which of the following statements, if true, most weakens Wiehle's theory that complex behavior could evolve only once?

(D) Plants in the Cactaceae and Euphorbiaceae families, although they often look alike and have developed similar mechanisms to meet the rigors of the desert, evolved independently. - Correct,

In the case of the Plants in the Cactaceae and Euphorbiaceae families, the complex behavior to meet the rigors of the desert evolved independently. Wiehle's theory postulates that the families must be related, based on the assumption that complex behavior, such as web building, could evolve only once.

One of the questions of interest in the study of the evolution of spiders is whether the weaving of orb webs evolved only once or several times.

An interesting debate is IF the spider web is the result of just one evolution or several ones.


About half the 35,000 known kinds of spiders make webs; a third of the web weavers make orb webs.


This is just a statistic. I reckon that it could be relevant because it is given so early in the passage.

Since most orb weavers belong either to the Araneidae or the Uloboridae families, the origin of the orb web can be determined only by ascertaining whether the families are related.

This specific kind of spider belong to two families at the same time. IF we do know to which family it belongs we could also to assess if the spider web it produces replies to the question posed in the first sentence. Quite sure.

Recent taxonomic analysis of individuals from both families indicates that the families evolved from different ancestors, thereby contradicting Wiehle's theory.

Recent conceptual investigations (taxonomic) tell us that, turns out, both families (two mainly) are the result of the evolution of SEVERAL individuals (animals/spiders), and this directly contradicts the W Theory. This means this W theory, maybe, sustained that the families originated from ONE or just a few spiders



This theory postulates that the families must be related, based on the assumption that complex behavior, such as web building, could evolve only once.

The theory tells us that complex or not simple behaviors result from just one evolution. Probably the relation is kinda like the following

complex= one straight behavior and ancestor. The families are related each others

According to Kullman, web structure is the only characteristic that suggests a relationship between families.

The spider web is the linkage between the two families

The families differ in appearance, structure of body hair, and arrangement of eyes. Only Uloborids lack venom glands.


The families have characteristics quite similar.


Further identification and study of characteristic features will undoubtedly answer the question of the evolution of the orb web.

We need further investigations to understand better.

17. The primary purpose of the passage is to

(A) settle the question of whether orb webs evolved once or more than once
(B) describe scientific speculation concerning an issue related to the evolution of orb webs
(C) analyze the differences between the characteristic features of spiders in the Araneidae and Uloboridae families
(D) question the methods used by earlier investigators of the habits of spiders
(E) demonstrate that Araneidae spiders are not related to Uloboridae spiders

C,D, and E are out of scope because too specific and they did not catch the main idea.

A as well.

the last sentence , also, tells us that we need further investigations

B is the answer

18. It can be inferred from the passage that all orb-weaving spiders belong to types of spiders that

(A) lack venom glands
(B) are included either in the Uloboridae or Araneidae families
(C) share few characteristic features with other spider types
(D) comprise less than a third of all known types of spiders
(E) are more recently evolved than other types of spiders

MMhhh at the beginning I thought was B. It is tricky

However, the passage says

Since most orb weavers belong either to the Araneidae or the Uloboridae families,

But the stem says

all orb-weaving spiders

\(most \neq all\)

D is the answer

19. According to the passage, members of the Araneidae family can be distinguished from members of the Uloboridae family by all of the following EXCEPT

(A) the presence of venom glands
(B) the type of web they spin
(C) the structure of their body hair
(D) the arrangement of their eyes
(E) their appearance

Easy one. B in 5 seconds

how the web spin is never mentioned in the passage.

We are wondering the evolution of the spider web NOT the type: rectangular, circular, and so on

20. Which of the following statements, if true, most weakens Wiehle's theory that complex behavior could evolve only once?


We need to find out a similar answer that mimics the assumption = complex behavior

(A) Horses, introduced to the New World by the Spaniards, thrived under diverse climatic conditions.

climate is not the same as complex

(B) Plants of the Palrnaceae family, descendants of a common ancestor, evolved unique seed forms even though the plants occupy similar habitats throughout the world.

similar habitats is not complex

(C) All mammals are descended from a small, rodent-like animal whose physical characteristics in some form are found in all its descendants.

This is a possible answer. Evolution ONLY once and , turns out, complex according to the W theory

(D) Plants in the Cactaceae and Euphorbiaceae families, although they often look alike and have developed similar mechanisms to meet the rigors of the desert, evolved independently.

evolved independently. This is better than C. We told us to weaken the ONCE evolution/complex. Yes. Evolved independently means different ways. More streams and NOT only once. This the right choice

(E) The Cuban anole, which was recently introduced in the Florida wilds, is quickly replacing the native Florida chameleon because the anole has no competitors.


quickly replacing the native is not complex or evolution


D is the correct answer

17. The primary purpose of the passage is to


(A) settle the question of whether orb webs evolved once or more than once

No. The last line states:

Further identification and study of characteristic features will undoubtedly answer the question of the evolution of the orb web.

Therefore, the issue is not yet settled.

(B) describe scientific speculation concerning an issue related to the evolution of orb webs

Yes.

This theory postulates that the families must be related, based on the assumption that complex behavior, such as web building,

According to Kullman, web structure is the only characteristic that suggests a relationship between families.

Further identification and study of characteristic features will undoubtedly answer the question of the evolution of the orb web.

(C) analyze the differences between the characteristic features of spiders in the Araneidae and Uloboridae families

No, this is not the primary purpose.

(D) question the methods used by earlier investigators of the habits of spiders

No mention of this in the passage.

(E) demonstrate that Araneidae spiders are not related to Uloboridae spiders

No, that is not the primary purpose.



18. It can be inferred from the passage that all orb-weaving spiders belong to types of spiders that

(A) lack venom glands

No. Only the Uloborids lack venom glands.

(B) are included either in the Uloboridae or Araneidae families

No.

Since most orb weavers belong either to the Araneidae or the Uloboridae families

whereas the question talks about all orb-weaving spiders

(C) share few characteristic features with other spider types

No mention of this in the passage.

(D) comprise less than a third of all known types of spiders

Yes.

About half the 35,000 known kinds of spiders make webs; a third of the web weavers make orb webs.

Thus, around one-sixth of all known types of spiders weave orb-webs, which is less than a third.

(E) are more recently evolved than other types of spiders

No evidence for this in the passage.



19. According to the passage, members of the Araneidae family can be distinguished from members of the Uloboridae family by all of the following EXCEPT

According to Kullman, web structure is the only characteristic that suggests a relationship between families. The families differ in appearance, structure of body hair, and arrangement of eyes. Only Uloborids lack venom glands.

(A) the presence of venom glands

No.

(B) the type of web they spin

Yes.

According to Kullman, web structure is the only characteristic that suggests a relationship between families.

(C) the structure of their body hair

No.

(D) the arrangement of their eyes

No.

(E) their appearance

No.


20. Which of the following statements, if true, most weakens Wiehle's theory that complex behavior could evolve only once?

This theory postulates that the families must be related, based on the assumption that complex behavior, such as web building, could evolve only once. So we need to look for a choice which postulates a complex behaviour which came from unrelated families.

Or we should look for a choice which describes something similar to the following

Recent taxonomic analysis of individuals from both families indicates that the families evolved from different ancestors, thereby contradicting Wiehle's theory.

(A) Horses, introduced to the New World by the Spaniards, thrived under diverse climatic conditions.

No. This is not natural evolution in the first place and no mention of their ancestral families.

(B) Plants of the Palmaceae family, descendants of a common ancestor, evolved unique seed forms even though the plants occupy similar habitats throughout the world.

No. Here the families are related, even though the seed forms are unique, so we reject it.

(C) All mammals are descended from a small, rodent-like animal whose physical characteristics in some form are found in all its descendants.

No, since they all descended from a small rodent-like animal.

(D) Plants in the Cactaceae and Euphorbiaceae families, although they often look alike and have developed similar mechanisms to meet the rigors of the desert, evolved independently.

Yes.

Here we have a common appearance and similar mechanisms but different ancestors (evolved independently), hence it contradicts Wiehle's theory.

(E) The Cuban anole, which was recently introduced in the Florida wilds, is quickly replacing the native Florida chameleon because the anole has no competitors.

No, this is not natural evolution, and it does not even address the issue of ancestors (common or otherwise)

That is just mentioned in the passage in the end as a characteristic NOt a difference, between the two species

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Hi can you please explain the answer for #20, I am not very clear with the weakens, specially in this context "Wiehle's theory"

Thank you for your replay, I am really having tough time to break down or simplify the sentence" Wiehle's theory postulates that the families must be related, based on the assumption that complex behavior, such as web building, could evolve only once" Do you think I can simplify, W's theory claim the families/ similar group must be related based on complex behavior and Could evolve only once? I am sorry if it sound really silly.

For Question 19 - since the passage says " only uruboridae lack venom glands" why can this not be a differentiator between the 2 families ?

Yes. It is a differentiator. The question is an EXCEPT question. And therefore, it is the WRONG ANSWER.