Instinct.  From the definition:  "An innate fixed behavior that is found without exception in every member of the species, and that presents itself full blown upon stimulation."

When you hear someone say that all people protect their babies, you know from experience that some people abuse and kill their children.  Instinct does not allow that kind of deviation.  There are entire courses that delve into the subject of instinctual behavior.

If you study sociology, you will, from the definition, conclude that man has no instincts.  There are too many deviations from the norm within the species.  But I believe that man has one instinct.  All tribes, aborigines, cultures, etc. that have emerged--that we call human, or that have been found archeologically--have one thing in common.  They make gods.  Totems, or they worship cows, snakes, or other animals.  They worship the moon, the stars, the sun and on and on...  They, without exception, look for the cause of their existence and design a god.  They make sacrifices. They know that there is "Something."  They seek to fill some empty place within themselves.

God created that empty place.  And until it is filled, man will search for something to answer his questions about his existence.  Where did he come from?  Why is he here?  Is there something more?   Is there something in the sun, or the stars or moon?  No other species does these things except man.  God created this "chamber" within us in which He intended to live.  He breathed into us a living soul.  His Holy Spirit.  His very breath.  And without this Spirit, we are not whole.  We are always searching.  Looking to find something that will calm our fears.  That will give us peace.  That will take away the fear we have of death.

The entire Old Testament of the Bible is the story of God's plan to return His Holy Spirit to man.  To complete him once again.  To dwell in man--where God intended to dwell from the beginning.  "Christ in you, the hope of Glory," is how the Apostle Paul described it.  All of us are the children of a man--Adam--who lost God's Spirit and was cast out of the garden of Eden because of disobedience.  We are born empty as an Adamic species...and we search for a God.  This God desires to be found.  To take up residence within us and make us whole.  He loves us and was willing to take our sin and die in our place.  We have an instinct.  We want God.  And for some reason, He wants us.