Question 1
The late zoologist Sidnie Manton acknowledged that arthropods- animals with jointed exoskeletons, such as flies, crabs, and spiders- are all descended from soft-bodied segmented worms. Yet he maintained that differences in limb form, musculature, and embryonic development indicate that these three arthropod groups- insects, crustaceans, and chelicerates, respectively- evolved independently from worms rather than from a common arthropod ancestor. Consequently, according to Manton, shared characteristics such as a jointed exoskeleton and large compound eyes represent cases of convergent evolution- similar yet independent developments- in these organisms. But if they evolved convergently, then one would expect significant differences in the neurological systems supporting sight. In fact, however, many nerve cells play virtually identical roles in supporting complex visual responses in both insects and crustaceans, suggesting that their common ancestor already possessed highly developed eyes, and therefore was probably already an arthropod. Yet the compound eyes of chelicerates differ neurologically from those of insects and crustaceans, suggesting that the eyes of chelicerates did evolve independently and providing partial confirmation of Manton's views.
It can be inferred from the passage that Manton believed which of the following about the 'shared characteristics' mentioned in the passage?
Rationale
Manton believed that the shared characteristics indicate that all three groups of arthropods descended from segmented worms.
Manton acknowledged that the jointed exoskeleton and large compound eyes are shared traits among insects, crustaceans, and chelicerates, suggesting that these features were present in their common ancestor, which was likely already an arthropod.
A) The shared characteristics are not all present in any single ancestor of these three arthropod groups.
This choice misinterprets Manton's views, as he suggests that the shared characteristics do indeed point to a common ancestor that possessed these traits, rather than asserting their absence in any single ancestor.
B) The shared characteristics could be used to determine which of these three arthropod groups gave rise to the other two.
Manton's argument focuses on shared traits indicating common descent rather than the direction of evolutionary lineage among the groups. Therefore, this statement does not align with his perspective on shared characteristics.
C) The shared characteristics are a good indication that all three groups of arthropods descended from segmented worms.
This is correct, as Manton posits that the shared features among the arthropod groups suggest a common ancestry linked to segmented worms, confirming the descent from a shared ancestor.
D) The shared characteristics are the most compelling evidence to date for the theory of convergent evolution.
While Manton discusses convergent evolution, he attributes the shared traits to a common ancestry rather than viewing them as evidence of convergent evolution, making this statement inconsistent with his views.
E) The shared characteristics do not justify classifying all three animal groups as arthropods.
This choice contradicts Manton's acknowledgment of the traits that affirm their classification as arthropods, as he implies that these characteristics support their common identity rather than undermine it.
Conclusion
Manton's analysis presents a nuanced view of arthropod evolution, indicating that the shared characteristics among insects, crustaceans, and chelicerates not only suggest a common ancestry but also reinforce their classification as arthropods. While highlighting convergent evolution, he maintains that these traits originated from a shared ancestor rather than emerging independently, underscoring the complexity of evolutionary relationships within these groups.