sayantanc2k
Yes, probably I understand your point. That is the reason I suggested that "that of" is required before "malaria":
....coincidence of the geographic range of the sickle cell gene and THAT OF malaria...
Instead, let us consider that the singular "geographic range" is changed to plural "geographic ranges" as follows:
....coincidence of the geographic rangeS of the sickle cell gene and malaria...
This in my view is slightly ambiguous. This usage may imply that the multiple ranges are common for both sickle cell gene and malaria. The idea that two different ranges (one of sickle cell gene and the other of malaria) coincided is not very clear. The "car" example above would probably make the problem clearer:
The cars you and I have are blue...... this may imply that you and I own the same cars, and those cars are blue.
The car I have and that you have are blue.... this makes it clear that your car and my car are not the same, and they are blue.
Did I understand your point correctly?
Exactly. If the GMAT sentence had said "that of" there would have been no ambiguity. Unfortunately, this is only hypothetical.
The reality is that the "geographic range" in the sentence represents two geographic ranges, so grammatically it should be plural. I'm sure there is a reason for the singular form to be correct, some kind of exception, but what is it? How can we generalize this reason, this rule, this exception?
In the car example, let's try to make it resemble the GMAT sentence even more:
"The car of mine and that of yours"
Now, without the option of saying "that of", which is the case in the GMAT sentence, would you say, with the objective of retaining the original meaning,:
"The car of mine and yours"?
I think saying it that way would imply there is only one car. Likewise, saying "the geographic range of the sickle cell gene and malaria" implies only one geographic range.
Or maybe there is in fact only one geographic range?
there has to be two distinct entities, not one - one entity cannot coincide all by itself. Hence there must be two
(one of SCG and the other of M). Therefore in my view the usage of singular or even a plural that belongs to both the groups simultaneously is not correct - there has to be two different groups that concincide.