The nutrients in food are exposed when heated. This makes it is easier for our digestive enzymes to do their work effectively, extracting more calories more quickly than if we ate our food raw. The extra energy it gave us allowed us to evolve the small colons and relatively large energy-hungry brains that distinguish us from other primates.

And, as our brains began to grow larger and smarter it created a positive feedback loop and we figured out more ways to to access the calories in our food.

Around 12000 years ago, global temperatures rose rapidly and then stabilised. Within 2000 years people all over the world started domesticating crops. 

Cultivating crops had been pretty much impossible during the Ice Age but the new warmer climate, coupled with a big rise in carbon dioxide levels, was very hospitable to plant life.

More food meant more people - who could then expand into new territory, and develop new technologies that produced even more food. 

The surplus energy agriculture created meant we could sustain much larger populations. Everyone didn't need to farm anymore and people could specialise in other fields or arts. Civilizations now started developing. 

Hunter gatherer communities tend to share resources fairly equally. In farming communities, by contrast, deep inequalities can develop.

People in civilizations worked double the amount than a person in a hunter gatherer society and only kings and nobles enjoyed a leisurely life.

By the 18th Century, our increasingly populous societies were beginning to run up against the limits of agriculture.

Then we found coal that we could dig up and burn in almost unlimited quantities which contains the solar energy captured over millions of years by fossilised forests. Oil and natural gas proved even more valuable.  

Not only were fossil fuels abundant. They also provided ever greater sources of power, liberating us from our dependence on animals for farming and transportation.

Since the Industrial Revolution we have grown taller and healthier, our life expectancy has increased vastly, and in the developed world we are on average 30 to 40 times better off.

We live in a fossil fuel society. But while they proved to be extremely valuable, the catastrophic climate change they are creating now threatens to derail that society. Two centuries ago we reached the limits of what agriculture could do, now global warming is imposing a limit on what fossil fuels can safely do. 

It has created the greatest challenge human society has ever faced - moving back to relying on the daily influx of energy from the Sun to meet the huge energy needs of eight billion people and counting.