Some teachers tell their students that animals should be referred to as "it" and "that" unless you know the animal's sex or unless the animal has a name. This advice is only half true.
In stories and newspaper articles animals are more commonly referred to as she or he, the word it is used only when the animal's sex is unknown. The word that is more often used (as a relative pronoun) instead of the word who if the animal is unnamed. A named animal is treated as a person.
The monkey that climbed into the building stole some fruit.
Tom, the pet monkey who escaped, stole some fruit.
Animals are referred to as it if their sex is unknown. Humans are not, the word they (as the third person gender-neutral) is used instead. (Sometimes the word he is used if a human's sex is unknown, but this is a sexist, and fairly recent, use.)
The monkey was caught after it stole some fruit.
The monkey, Tom, was caught after he stole some fruit.
The monkey escaped and it stole some fruit.
Someone broke into my house and they stole a CD player.
However in science textbooks and farm reports, the word that is used more often than who to refer to the animals. Laboratory and farm animals usually do not have names and aren't pets. Unnamed animals are things and are not treated as people.
Last week we looked at the fake rule about not using the word that to refer to categories of people. Those same that/ who structures apply to animals as well as people. Categories of animals are referred to as that.
The first point to make is that these are style choices. (They are suggestions, not rules) The second is that certain types of texts call for different styles. The word who is used more often in stories for pets and named animals. The word that is used more often in factual reports for unnamed animals.
Next week I'll cover the use of who or that for organisations.