It’s our ability to control fire that made us human.  This is the message of Richard Wrangham’s new book, ‘Catching Fire’,  which was published last year.  It’s the latest big idea in evolution, the one that Darwin ignored.    

Wrangham approaches the subject from the perspective of an anthropologist and primatologist; he has worked at Gombe with Jane Goodall.  His hypothesis extrapolates from three sets of observations.  First, when food is cooked, nutrients are more easily digested and assimilated into the body.    Cooking softens meat, loosening connective tissue and allowing enzymes access to muscle proteins and fats.   Cooking also breaches the rigid cell walls of plants, exposing starches and sugars and vegetable fats to digestion.  Cooked meals require less work and less time to eat them.  Less effort needs to be spent in finding food that can be easily digested.  Cooking saves us time; time to think, to plan, to bond and it has to be said, to eat more food. 

By comparison, other mammalian species spend the majority of their time hunting, feeding and digesting their food.  Sheep and cows would never get enough energy to reproduce if they didn’t eat all day.  A male tiger needs to spend nearly all its waking hours hunting.  Only when it has had a big blow out, can the tiger afford to rest up and digest.   

But for humans, it’s different. They had time.  People gathered around their fires in the evening to tell stories, to sing, to drink, to plan the next day’s activities and to make love. It was around the hearth that tribes forged their identity in mythology. Fire became the focus of the social group, the hearth, the forge of civilisation. Cooking expanded the range of foods that could be eaten.  This meant that people didn’t have to hunt and gather particular foods; they could cultivate and herd them in farms.  This allowed people to settle in villages, towns and cities.  

Fire also led to a division of labour. Women were the cooks, the keepers of the fire, the gatherers and of course the mothers, whereas men were the hunters, the farmers and the protectors.    

Not only has fire enabled human beings to evolve socially, Wrangham believes that they have also adapted anatomically and physiology to eating cooked foods.   Our jaws are much weaker than our closest cousins, the chimpanzees; not at all equipped for cracking hard nuts and seeds or for tearing meat.  Our large intestines are nowhere near as commodious and efficient at extracting nutrients from uncooked vegetable matter.  People can live on raw food if they spend time seeking out and preparing foods that are sufficiently soft, but they lose weight and tend to become infertile.  Thus it seems we have evolved into a culinary ape.   Perhaps even our hairlessness was an adaptation to the control of fire.  Did fire allow us to dispense with fur and become the naked ape.        

The important thing about a good hypothesis is not that it’s right but that it makes you think.  Wrangham’s hypothesis certainly makes us think , but it is probably not entirely accurate. 

 We are not the only species with small guts.  Carnivores,  dogs, cats have much smaller guts probably because they don’t need a big fermenter to break down complex plant material.  Perhaps the early homonids were predominantly hunters and scavengers; they ate predominantly meat and were strategically adapted to hunting and trapping animals.  But their poor dentition may indicate that they lived on soft body organs or even on food that was half rotten with some additional fruits and leaves.     

 Cooking is not the only way of softening food, acid in the stomach does it too.  After they have made a kill, lions and tigers need to rest for several hours for acid digestion to occur.  The acid in human stomachs is as strong as that in other carnivores.  The thing is, we can survive without cooking.  We can all eat raw food though we may not have much time for anything else.  Cooking saves time.          

But is there any evidence in the fossil record that links the development of humans with fire?   Humanoids with the characteristic shape that we have now,  Homo habilis and Homo erectus,  appeared about two and half million years ago, but the earliest evidence we have of hominids  controlling fire is 750,000 years ago.     

So was cooking the big breakthrough that allowed human beings to evolve into a more physiologically efficient mammal by relying on an external source of energy?   Did we develop our human shape and physiology because our ancestors had learnt to harness fire?   Or was  cooking an evolutionary accelerant rather than an instigator? 

According to Darwin’s deductions, evolution of species does not tend to occur gradually over millions of years, it is jerked forwards by environmental change;  only certain individuals were sufficiently equipped to survive and breed under the new conditions and they produced more individuals with the same improved adaptations. 

The accepted wisdom is that human evolution was instigated by climate change in sub-Saharan Africa.  Less rainfall led to a dying back of the rainforest and its replacement by savannah.   Certain of our ancestors could survive at the edges of the forest.  They learnt how to trap and kill the grazing animals for food.   Some had a more flexible thumb that could be opposed to the other digits allowing them to grip and manipulate tools.  These better equipped individuals could make and use tools, they could fashion weapons, they could throw things;  they could project into the future.  These adaptations led quickly to others.  Only those with the most efficient weaponry and skill, would survive, the rest would be killed off. 

Genetics provides the potential, the environment brings it out.   The brain develops according to experience, though some brains are more adaptable.  In a rapidly changing environment, only those apes able to adapt, survive.  So, over relatively few generations, a sub culture is selected out.  Seen from this context, fire is another tool, something the advancing ape learnt to control, but it rapidly became indispensible. Hominids adapted to it and indeed could not survive without it.  Fire now does so many other things besides cooking, it drives engines that make things and get us places.  And now we have discovered enormous supplies of fossil fuels, we are totally dependent on the energy it gives us, so much so that few of us would survive without it.  And yet, supplies of fossil fuel are finite.  They will be depleted in 30 years.