Every species on earth seeks out companionship, but love is something that is unique.  Humans are the only species known to care about such things as looks, personality, goals in life, etc.  Other species simply mate and get on with their lives. I think that humans seek out love because humans are a very codependent species. They (we) rely on each other tremendously to help each other through difficult situations.  It has been scientifically proven that humans do not function well when alone.  After extended periods of time without human interaction, the brain function declines steadily at a slow rate.  Humans need each other. There is not a simpler way to state this than to say that humans need each other. They (we) need love and compassion to keep them (us) healthy and alive. It is human nature to go out into the world seeking love, understanding, and compassion. Not unlike Frankenstein's monster who craved another body to sympathize along side him, humans crave this as well.