Whatever the family's agreement may be, it is always based on mutual trust.
No family can exist if one of its members is mortally afraid of being harmed by another member.
There are no spider families because female spiders try to devour the males.
On the other hand, two wolves living together are ferocious animals that can harm each other considerably.
The fact that they are a pair means that they have an agreement not to do so, as well as a pact to fight for those things that are for their mutual good—because mutual protection is also part of the family contract.
Thus, without signing any legal papers, when the female bird is hatching the eggs, the male bird feeds it, and in that relationship both partners perform their share of the agreement.
–Rabbi Adin Steinsaltz
From "Family" in Simple Words by Rabbi Adin Steinsaltz