There's even a great deal of biological study backing this up. A male will defend his young, even though they were never physically bonded nor hormonally morphed via pregnancy. Females on the other hand must be chemically influenced in order to develop maternal instincts and form a bond with their offspring.

When that hormonal dosing is imbalanced you can see some of the worst cases of postpartum depression (insanity). This imbalance is used as a legal defense for infanticide.

But the other side of the coin, no one wants to admit that maternal instincts / love for the offspring in females to a hormonal derivative.