This is the 706th most frequent Polish word.
niektóre
"Niektóre" means "some" in English.
The word 'niektóre' is used here as an indefinite pronoun meaning 'some' to specify an unspecified subset of items from a larger group (books).
Niektóre książki na tej półce są naprawdę interesujące.
Some books on this shelf are really interesting.
In this sentence, 'niektóre' refers to an undefined subset of individuals within a specific group (people).
Niektóre osoby w grupie miały różne zdania na ten temat.
Some people in the group had different opinions on this topic.
Here, 'niektóre' is employed to indicate an unspecified subset of the broader category (animals) adapting to particular conditions.