Garry Tan wrote two years ago:

I happened on an interview with Tufts University Professor of Philosophy Daniel C. Dennett that pointed out perhaps those cells really are warring: 

Each neuron is imprisoned in your brain. I now think of these as cells within cells, as cells within prison cells. Realize that every neuron in your brain, every human cell in your body (leaving aside all the symbionts), is a direct descendent of eukaryotic cells that lived and fended for themselves for about a billion years as free-swimming, free-living little agents. They fended for themselves, and they survived.    

It's an interesting thought experiment. At some point, single celled organisms started banding together. Oh, you know, about 1 billion years ago (clipped from an amazing infographic recently at waitbutwhy.com):  

After about 400 million years, those few early multi-cellular lifeforms got progressively more advanced, resulting in the first fish about 500M years ago, then insects 400M years, then reptiles 300M years ago, then mammals about 200M years ago.

So that's a lot of years for things to progress from just a few cells going on a date to now about 50 trillion cells coordinated in unison in any given human body! Though perhaps the most important part, the brain, consists of somewhere around 100 billion of them. 

So that's wild. The experience of one human being, my experience, and your experience, seems to be the product of 100 billion neurons working together — fighting, debating, forming alliances, and ultimately making decisions. 

That gives me some hope for humanity overall, then. If 100 billion in-it-for-themselves descendants of selfish eukaryotes can work together for the greater good, whatever it is you choose it to be — then perhaps 7 billion people can do the same for the humankind. 

The Wait but Why article is worth reading:

http://www.waitbutwhy.com/2013/08/putting-time-in-perspective.html