Halliday & Matthiessen (2014: 385):
Here again the grammar makes a categorical distinction: (a) conscious things, which are those referred to as he/she, (b) non-conscious things, those referred to as it. … while there is a clear foundation in the world of experience, with people at one end and inanimate or abstract objects at the other, many things (like non-human animals) lie in between; and, as always, the grammar is free to construe the world as it pleases.
The conscious/non-conscious distinction can also therefore be looked at as a cline; and it is one that has received a lot of attention in typological linguistics, under the name of animacy. This, as already remarked, refers to the likelihood of any thing to occur as Actor in a transitive material process, the ‘most animate’ in this sense being, obviously, post-infancy humans.