Spencer Wells has a job that most people would kill for. He is explorer-in-residence for National Geographic and his work has taken him to every corner of the globe. His particular interests have nothing to do with wild places, however. His fascination lies with the people who inhabit these remote corners: how did they get there and what are their biological relations with other inhabitants of the planet?

Wells is a geneticist and leader of the Genographic project, funded by National Geographic, which has traced the movements of human populations since we first emerged from our sub-Saharan homeland 100,000 years ago and colonised the planet. In the process of this work, Wells noted that a swath of genetic changes occurred to our species around 12,000 years ago.

This was a crucial period for humanity as it was around this time that agriculture began its inexorable spread across Europe and Asia, changing Homo sapiens from hunter-gatherers to farming folk. The consequences were profound and not always beneficial. They also point to future problems for our species, as Wells argues in his latest book, Pandora's Seed: The Unforeseen Cost of Civilization (Allen Lane).

Why did humanity turn to agriculture 12,000 years ago?

We were backed into a corner. Conditions changed at the end of the ice age 17,000 years ago and, as the climate got warmer, populations began to expand. Then there was a sudden reversal to ice age conditions during the Younger Dryas period 12,500 years ago. The land could no longer support that growing population and we had to innovate – by developing farming. It made sense in the short term, but there were consequences, both pleasant and unpleasant.

Give us some examples.

Before agriculture, humans were living on diets that included more than 150 plant species. Then we started farming and that figure went down to around eight. In fact, most calories came from wheat and barley, which are full of carbohydrates but have little protein. Human health declined sharply. We got shorter and life expectancy plunged. In many parts of the world, it has yet to recover.

You argue that there were other consequences for society.

Yes. When we were hunter-gatherers, we were relatively egalitarian. Then the population expanded and the first towns appeared. We had to find a way of ruling those people. So governments came into play. In addition, most hunter-gatherer societies today have a panoply of deities. Gods are everywhere. But as we started to control nature, we saw ourselves above nature. Gods start to take on a human form, so monotheism appears around this time.

Then there is the issue of sexual relationships, which were probably egalitarian, as they are among hunter-gatherers today. However, as we built more cities and, ultimately, empires, military might was needed and being physically strong and having military prowess became important. Men, being stronger than women, probably developed a higher social standing this way.

What about the future?

It is difficult to say what life is going to be like in 100 years, but certain things have clearly been set in motion, among them climate change. That is why I have developed the concept of transgenerational power – the idea that we are making decisions locally, in the here and now, though these will take generations to play out. We need more energy, so we pump the stuff out of the ground, but have only now realised, generations down the road, that there are unanticipated consequences.

Similarly, we are developing the ability to chose the genes we want for our offspring and, therefore, for our grandchildren and our great-grandchildren and so on.

Are we going to make the right decisions for the next century or the next millennium? We have not adapted psychologically to the notion of long-term consequences.

Can Homo sapiens do that?

We have to become capable of it. At the dawn of agriculture, there were around 5 million people on the planet. There are 6.8 billion today and this figure is expected to peak at around 9.5 billion by 2050. For the first time in 70,000 years, for lots of reasons, human numbers will have reached a steady state.

At that time, there will be more people moving into the retirement category and fewer people in the young worker category. There will be more people over 60 than under 15 for the first time in history – all over the world, not just in the developed world.

Will we be able to cope by 2050?

It is a question of utilising resources in a more intelligent way. I have a phrase for it: want less. I think that is the lesson we can take from current hunter-gatherer groups, people who still live in a way that our ancestors did. They live within constraints. We have got used to expansion and dominance. Learning to recognise that we have limitations is going to be important.

Are you hopeful?

I am because I think humans have the ability to innovate. The issue is seeing the consequences, realising that there is a cost to what we are doing and recognising that now. We are not adapted to think in those terms. But if we can see that there are tangible consequences to what we are doing in the here and now, then I think we will be spurred into action.