It is, I believe, generally accepted that who can be used to refer to animals (or at least some animals, or at least under certain conditions). Thus, Merriam-Webster’s online dictionary has this entry (I’ve outlined the key part in red):
However, Merriam-Webster’s online learner’s dictionary has this entry:
No mentions that who can be used for animals. And it isn’t only MW. I checked six learner’s dictionaries and none of them said this was acceptable, or an option. This isn’t a huge deal, necessarily, but it can lead to confusion if, say, this has been taught as a ‘rule’ and then students read graded readers where the ‘rule’ is broken without any consequence (search for horse who, fish who, or monkey who in the Lextutor graded reader corpus, for example). Of course, there are tons of sources where students might encounter who being used for animals.
This came up because a student of mine had written “I don’t want a dog who is so big” and a peer suggested it should be which. And that’s FINE. It can be which :-). Or that :-). But it can also be who :-D.
For teachers who like to do consciousness raising or language awareness activities, this kind of situation provides opportunities for discussions of things like what if you read/hear some language in real life that doesn’t seem to match what the dictionary/grammar guide says, analyzing lines of ‘controversial’ lexicogrammar patterns, or formulating ideas about why people choose to use who, or which, or maybe that in different circumstances (does it seem ok for certain animals but not others? is it special for pets? does it change the meaning/tone/nuance?).
Of course, the underlying ideas could be applied to other language questions, too. So, in general, the ‘corpus lesson’ here is that corpora can be used to explore alternatives to more conventional patterns and aid in developing greater language awareness. Corpus-use can be applied to not just learning frequent or common patterns of expression, but to expanding the ways in which learners are able to express themselves.
While talking about this with another teacher, it was suggested that maybe the learner’s dictionaries (and perhaps some other learner-oriented materials) don’t acknowledge who for animals as acceptable because it’s new (recent) and thus ‘non-standard’. But I have trouble seeing which of these would be considered ‘non-standard’ (in fact, I doubt that in many cases fluent English users would even notice this usage unless it were pointed out or they were looking for it). And it’s not really a recent thing, is it?:
Against the Capitol I met a lion,
Who glared upon me, and went surly by
This corpus-based analysis (Gilquin & Jacobs, 2006) of who being used with animals may also be of interest.