Why do we do the things we do? What choice do we have? Who or what does the choosing? My research into these questions revealed 10 recurring and highly characteristic forms of human behaviour. From the Aggressor to the Nurturer and the Ostraciser to the Rescuer… you may well recognise some of these tropes. If they are familiar, it’s because you carry elements of all of them inside you. In a sense, they are you. Only they’re not – not entirely. Aspects of them inform and shape the most important decisions in your life. But you’re almost certainly unaware of their intervention. They are the essence and instinct of the people you meet.

For years our brain was thought to function like a general-purpose computer, an old-fashioned telephone system in those black-and-white movies, with everything going through a central switchboard. This view is being challenged. New findings in neuroscience and evolutionary biology indicate that the brain may be more intriguingly fragmented than that.

Instead of a clunky computer, it may be more like a smart phone equipped with a series of highly specialised “modules”. Each one has developed in the face of specific adaptive problems or evolutionary goals. They help cope with certain key, recurring problems in human life. This is the concept of “modularity”.

Violence blights our world like almost nothing else, yet almost all of us have an aversion to inflicting harm on others

Our brain is not immune to evolution. The modules that were relied upon for survival in millennia past still shape our lives in important ways. I identified at least 10 of these “modules” in our mind. Some are deeply destructive – something I have witnessed as a human rights lawyer for more than 25 years. My practice has been about carnage. The hidden parts of us that significantly affect the triumph and tragedy of the human race.

As Harvard professor EO Wilson states: “The worst in our nature coexists with the best… the monster in the fever swamp.” This is not a new thought. In fact, it is almost our oldest. Sophocles saw it. In Antigone he tells us: “Many things are both wonderful and terrible, but none more so than humans.” We want to believe humankind is good, but we see so much wrongdoing – carnage – around us. Where does the truth lie?

Every year we make five million children work as slaves; three million more girls suffer unnecessary FGM; and we enlist hundreds of thousands to fight as frontline troops or concubines for commanders in our bloodiest wars. Yet, and here is the crucial paradox of our species, almost all of us also have a deeply wired empathy system. Many people around the world risk their lives to fight these social injustices.

There is a complex connection between the dark and light in our minds. Human-on-human violence blights our world like almost nothing else. And yet almost all of us have an aversion to inflicting harm on others. There remains a deep tension between this revulsion of violence and one element in our make-up, the Aggressor, that can respond in a multitude of nuanced ways with subtle threat and strategic violence. Yet the Aggressor is not who we are; we are not determined or defined by it. Aggression is just one of the things we can do. We also have other qualities. We have empathy; we sacrifice. This is an argument we have been having for centuries. And if it cannot be ultimately resolved, we can say that we are not the Aggressor and the Aggressor is not us. If anything that reductionist misrepresentation is one of the most vital things we must fight against.

To buy a copy of Ten Types of Human by Dexter Dias (William Heinemann, £25) for £21.25, go to bookshop.theguardian.com