Love
There are two types of people.
Those who think love is purely a product of evolution that exists to advance the fitness of a species and can be explained logically in its entirety;
And those who awe in the face of love, its power, its ability to defy logic, those who recognize true satisfaction, true fulfillment is only achieved through love, those who see love as not purely the product of evolution, but rather a force that predates creation. Those who see love as essential to existence.
Love is the force that pulls us closer, that pulls us together.