Q: SAT question, pronoun "their" I've been practising for the coming SAT, and I got confused by this question from the writing section. It read something like this:

John was one of the astronomers who devoted all their time to science.

It was in the error identification section, and the insidious error was in the pronoun "their". Could you please explain this to me?
UPD:
I'm sorry, my fault. I've found the original, and now I clearly see the error.
Here is the original sentence:

George Thornton Emmons was one of a handful of ethnographers who
  committed their life to studying the Tlingit culture of Northwest
  Coast.

The error is obviously in "life". It should be "lives". I feel ashamed of myself. Sorry I bothered you, and anyway, thank you for your responses.

A: It is grammatical. 

John was one of several astronomers who devoted all their time to Science.

"their" refers to "several astronomers" and John was just one of them.
"Mary Ann is one of the girls who are going to run the marathon."
" 

A: There is absolutely nothing wrong with the original sentence.
There would also be absolutely nothing wrong with this alternative, which is probably what the examiners wanted:

John was one of the astronomers who devoted all his time to science.

As FumbleFingers pointed out, this is partly because some (archaically) believe that 'he' is the only suitable gender-neutral pronoun.  
In this case I think there are reasons why one might pick one over the other, because it can emphasize whether it's John or some anonymous group of astronomers devoting their time to science.

A: I think the point is the sentence is about John. The fact that John is an astronomer is secondary. Therefor the pronoun should relate directly to John.
That being said, I've no problem with the sentence you were given either, since it seems to me that the sentence could equally be perceived to be about a life of science, which makes the astronomers more important since John is only a small part of the group that devote their life to science.
Seems like a silly point to grade people on unless you've specifically been told an order in which you should focus on nouns in sentences. 

A: I'm assuming they're looking for "his" instead of "their", since "John" would seem to be the subject of the sentence.
However, "the astronomers" are the subject. John is one of them. "The astronomers who devoted all their time to science" is a noun phrase. That John is a member should not affect the construction of that noun phrase. The Elements of Style says this:

A common blunder is the use of a singular verb form in a relative clause following "one of..." or a similar expression when the relative is the subject.
Incorrect: "One of the ablest scientists who has attacked this problem"
Correct: "One of the ablest scientists who have attacked this problem"

If you wanted to construct a sentence where "his" would be more appropriate, you could say, "John, one of the astronomers, devoted all his time to science".

A: The proper answer is:

John was one of the astronomers who devoted all his time to science.

"... devoted all his time to science." refers to John, not the astronomers.
It is common in everyday speech to hear their in place of his or hers but it is grammatically incorrect. 
