The cause of all war boils down to sex and social status, according to a conflict expert who used to be in the British Army

• Business Insider spoke to Mike Martin, a former British Army officer and conflict expert.
• Martin's new book Why We Fight is about the evolutionary psychology of warfare.
• He told us about the two reasons that people fight in wars.

Read the full transcript below:

Mike Martin: Hi, my name is Dr Mike Martin. I'm a former British Army officer and an expert on conflict and I've just written a book called Why We Fight about the evolutionary psychology of warfare.

The real question is, how have we evolved as individuals to fight for our groups? When you dig into it and you look at the data, there's only two things that are worth risking yourself in war for, as an individual. The first thing is an increase in social status. And the reason why that's worth risking yourself for is as you rise up the status hierarchy, particularly as a man, and men do most of the fighting, you get more mates, more sexual mates. When you have more mates, you have more children. That's a reason to risk fighting in war.

But there's another reason why people fight in war. That's to ensure that they have membership of an in-group. This in-group could be a tribe or a nation-state. It's the same mechanism, it's the thing that causes us as humans to feel belonging. It's the thing that makes you feel homesick. It's the thing that sends shivers down your spine when you're at a political rally, or a football match, or you're singing in a choir in church. These are the mechanisms in your brain causing you to seek to belong.

In evolutionary terms, we need to belong to groups because they're safe. The main reason that groups exist in evolutionary terms is because they protect us from other humans who are trying to kill us. We fight for status and we fight for belonging. We've got these ideas that these two things, status and belonging, and humans seeking those things are what cause individuals to fight in wars.

Actually, this makes sense. Look around the world. We've got two global level politicians and the idea of them seeking status and having status disputes with each other is very obvious in their behaviour. Leaders seek to dominate their own groups and that's what they do. Running for the presidency of the United States is a massive status contest, it's gruelling.

These people are driven to succeed and they're driven to achieve high status. The mechanism that guides this seeking status is basically testosterone. The way it works is that the more testosterone you get, the more you seek status, but it's a feedback loop. It's a positive feedback loop.

When you get to the top of your group, i.e. you become the leader of your country or perhaps you become the head of your tribe, it depends what scale we're looking at, you then seek to dominate other leaders who are the leaders of other groups. This is where we see wars at a product of a status disputes between leaders playing out.

Belonging comes into play when those who aren't leaders seek to take part in wars. We can see this played out and the rise of identity politics at the moment, particularly in the States, but also across Europe. If why we fight is correct and war is driven by status and belonging, we're entering a very dangerous period of history."

Produced by Charlie Floyd.