Warning! You have been fooled by science. As Man fumbles in the dark, restricted by His infantile knowledge, perceptions and severely limited senses, in His search for an understanding of existence, life and the meaning thereof, He is essentially separating the 'physical' from the spiritual and denying the primary entity, force and aspect of all existence.

The missing factors in Man's scientific and biological equations is the force His instruments cannot detect and His knowledge is therefore all flawed.

>For the wisdom of this world is foolishness with God.

Man is obsessed with a beginning for everything, but a beginning is not possible. Wherever there is a beginning, there must have been something in the time before. There can be no end, for after the end, there would still be time and whatever else was left. 

Indeed, nothing of a primary nature, omnipresent intelligence, energy, space and time can ever be brought into existence or removed from existence. Energy can be transformed into different 'material' forms and space and time may appear different as a result, but all things material are comprised of structured energy and structured and maintained by omnipresent intelligence.

While the physiology of the biological systems of earthly creatures include the triggers you speak of, these by no means explain the nature of love but are, as you stated, instruments of manipulation. 

God is love. The glory of God is intelligence and God gives structure to all things, i.e. creates or organizes all things and maintains the balance which facilitates the manifestation of structured energy in the myriad forms we observe through our senses and instruments.

We are all part of the entity which we call God and understand very little about. God is indeed present in all things, maintaining all structures, from atomic to cosmological level. Without the omnipresent intelligence, all structures would revert to pure energy.

This explanation is very crude, as my perceptions are, like almost all men, marred by incapacity.

> He who thinks he knows, is the one who is fooled. For our embryonic nature is currently incapable of understanding the realities of existence, for we are like fish in a bowl, remove from real contact with reality by the temporary veiling of our primary sense. 

Sources : The KJV and the Book of Moses, The Doctrine and Covenants.