Certain groups of Asian snails include both “left-handed” and “right-handed” species, with shells coiling to the left and right, respectively. Some left-handed species have evolved from right-handed ones. Also, researchers found that snail-eating snakes in the same habitat have asymmetrical jaws, allowing them to grasp right-handed snail shells more easily. If these snakes ate more right-handed snails over time, this would have given left-handed snails an evolutionary advantage over right- handed snails, with the left-handed snails eventually becoming a new species. Thus, the snakes’ asymmetrical jaws probably helped drive the emergence of the left-handed snail species.
Which of the following would, if true, most strengthen the argument that asymmetrical snake jaws helped drive left-handed snail evolution?
A.In one snake species, the snakes with asymmetrical jaws eat snails, while the snakes with symmetrical jaws do not eat snails.
B.Some species of Asian snails contain either all right-handed snails, or all left-handed snails.
C.Anatomical differences prevent left-handed snails from mating easily with right-handed snails.
D.Some right-handed snails in this habitat have shells with a very narrow opening that helps prevent snakes from extracting the snails from inside their shells.
E.Experiments show that the snail-eating snakes in this habitat fail more often in trying to eat left- handed snails than in trying to eat right-handed snails.
Situation There are both Asian snails with shells that coil to the right and Asian snails with shells that coil to the left, and the latter have evolved from the former; furthermore, there are snakes that have asymmetrical jaws that allow the snakes to grasp the snails with right-coiled shells more easily.
Reasoning What fact would help support the claim that the snakes’ asymmetrical jaws helped drive the emergence of species of snails with left-coiled shells? We are told that if over time the snakes with asymmetrical jaws ate more snails with right-coiled shells than snails with left-coiled shells, then this would give snails with left-coiled shells an evolutionary survival advantage. So, if some evidence showed that the snakes with such jaws in fact were more likely to have successfully eaten the snails with the right-coiled shells, then we would have good reason to think the snakes’
asymmetrical jaws helped drive the emergence of snails with left-coiled shells.
Correct. The fact that experiments show that the snakes are more successful at eating snails with right-coiled shells than they are at eating snails with left-coiled shells would support the claim that these snakes did in fact eat more snails with right-coiled shells, and hence the snails with left-coiled shells would as a result have an evolutionary advantage.
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