This is a transcript of an episode of Public Address Science which was originally broadcast on Radio Live, 8th September 2007, 5 pm - 6 pm.
You can listen to the original audio version of the programme by clicking on the 'Play the audio for this post' link at the top of this page or the 'Audio' button at the bottom of this page.
[Short sound sample from 2001: A Space Odyssey]
In the somewhat overwrought opening sequence of the film 2001: A Space Odyssey, our primitive ancestors are depicted as making a leap in development when they receive enlightenment from what appears to be an enormous singing block of Lego.
In fact, the reality of our ancestors' first paradigm shift in cultural development -- with the discovery of fire -- was almost equally as dramatic. Last week, I talked about humankind's ability to harness non-food forms of energy; the scale of which distinguishes us from all other animal species. And fire is where it all started. For the first time, a species was making use of the solar energy stored by plants not via the process of eating them, but by burning them: thus releasing the stored energy at a much higher rate than would otherwise be possible.
Now the conventional view of history is that as civilization has slowly developed, so new forms of energy have been harnessed. But over the next few episodes, I'm going to argue that that point-of-view is exactly the wrong way around. What I'm going to propose is that the harnessing of new forms of energy (or the exploitation of old forms in dramatically more efficient ways) has allowed humankind to make paradigm leaps in development -- and it is only after these leaps in development have taken place, that new forms of civilization have been able to grow and flourish.
[Sound of fire burning]
And the very first of these paradigm leaps occurred when ancient hominids exploited the energy in plant material by burning it. The date of fire's first use is somewhat disputed by anthropologists, but a reasonable mid-point figure of the various theories would be around five hundred thousand years
ago (although there's evidence that it could be as early as one-and-a-half million years ago).
What isn't disputed, however, is fire's enormous impact. The thermal energy (or heat) released by the combustion of plant biomass not only enabled early hominids to ward off predators -- but also enabled them to hunt game much more effectively, by using fire to flush animals out of forest areas, and into places where they could easily be slaughtered .
Furthermore, the judicious burning of vegetation enabled large-scale modification of the local environment. The removal of scrub and forest by fire made it possible to produce the conditions which favoured edible plants for gathering, or to create the types of habitat (and stimulate the secondary growth of vegetation) that would attract game animals for hunting .
And not only that, but small controlled 'camp' fires provided light during the night, and -- more importantly -- produced sufficient supplementary heat to enable hominids to spread out from their original habitat in the tropical regions, and migrate vast distances into Northern Europe and Central Asia .
[Sound of potatoes boiling on gas cooker in kitchen]
And lastly, of course, fire enabled the cooking of foods.
Cooking is something we do so often that we almost forget the many benefits that it provides. For a start, it allows the human digestive system to extract a greater quantity of energy from meat and many edible plants . It also kills food-borne diseases and parasites (a fact that's quite reassuring if you're ever invited to dinner at a student flat).
And, of course, cooking makes palatable otherwise inedible plants  such as acorns, cassava, karaka berries, and -- one of the foods I'm preparing tonight -- potatoes. Fire even allows the preservation of food through drying and smoking
[Sound of wind over high-tension power lines]
But it's one of the implications of food cooking that's perhaps the most interesting point about the early use of fire. You may not have noticed, but I've been very careful to use the word hominid rather than human. That's because the first beings to harness energy by burning plant material weren't human -- they were of the species Homo erectus . And they were using fire in a controlled manner for at least three hundred thousand years (or possibly much longer) before the arrival of Homo sapiens (modern humans).
[Sound of chewing]
Now some anthropologists have speculated that the ability to cook food with fire was especially important. They theorize that cooking acted to de-emphasize the evolutionary importance of chewing, and therefore made the skull strength required to support the massive jaw muscles found on Homo erectus much less necessary. And, in turn, this made it possible for subsequent hominid species (such as humans) to function with larger less-sturdy skulls, which could house correspondingly bigger brains .
If this theory is correct, then it could be said that fire didn't just enable early human civilization to develop -- but that the harnessing of fire by earlier hominid species actually made it possible for human beings to come into existence in the first place. And if that isn't a dramatic consequence of energy usage then I don't know what is.
[Sound of fire burning]
Now it's a fascinating (and slightly bewildering) fact, that although fire has been used by hominids for perhaps half a million years -- for most of that time, nobody actually knew how to make it. Again, the exact date is uncertain, but a ballpark mid-point of the estimates for when humans first
figured out how to use fire-bows, fire-saws, or flint to produce a flame, is around 10,000 BC  -- ironically, just in time for the end of the last ice age.
Before then, fire was gathered from naturally occurring events -- predominantly as a result of lightning strikes. Once gathered, the fire had to be kept constantly burning in sheltered locations such as caves, although it could be transported over quite long distances by carrying embers (damped with soil, moss, or leaves)  in receptacles such as hollow logs. However this was a risky business, because for early hominids the consequences of fire going out could very easily prove fatal .
The ability to make fire (rather than just gather it) was one of the first steps in what some have termed the Neolithic (or new stone age) revolution. The very next step was another dramatic change: the development of agriculture.
[Sound of a New Zealand farm]
It's been suggested that hunter-gatherers' manipulation of the landscape through fire to favour their preferred types of plant and game, led naturally onto the concept of domesticating animals and crops. That's something that will probably never be proved one way or the other, but what can be asserted without contradiction is that (with the possible exception of certain riverine habitats) Homo sapiens could only embrace agriculture by the use of fire .
Fire created the type of pasture that I'm standing in now -- which is required for grazing animals. It purged the fields of weed seeds and pathogens prior to the planting of crops. It promoted nitrogen-fixing bacteria, and the ash from fire released valuable nutrients into the soil. Until the advent of fossil fuels the energy required to perform these tasks was simply not available from any source other
than the burning of plant biomass.
In fact, the Neolithic style of agriculture with fire -- termed fire-fallow farming  and fire-forage herding  -- is still being used today. Controlled burn-offs are an annual event on many modern farms in New Zealand and elsewhere in the world .
[Sound of horse hooves on cobbles]
Agriculture brought a population explosion, and the development of permanent human settlements such as villages, towns, and eventually cities. And, of course, it also led directly to humankind's second great source of energy: animal labour. By 3000 BC pack animals were being widely used in North Africa, Europe, and throughout Asia  -- a development which greatly increased both the quantity and range of trade goods. And, shortly after this date, archaeological evidence shows that animal power was being used to pull ploughs and haul wheeled vehicles in what is now modern-day Iraq .
[Sound of a blacksmith working]
But energy from animals was only possible with agriculture, which, in turn, required energy from fire. The next technology that would arise from the flames (so to speak), would propel humanity right out of the stone age -- and into the age of metals.
But more on that next week, when we visit one of the great cities of the ancient world: Alexandria.
- Read about the Palaeolithic period in Wikipedia.
- Read about the Neolithic period in Wikipedia.