Scorched earth

Our long history with fire

I just spent two nights in a cabin in the rainforest high up on the Tablelands of Far North Queensland, Australia. Despite the area sitting snugly within the wet tropics, winter evenings are pretty cool up there. And so, for two nights, I reverted to what I used to do on winter nights when I still lived in a more temperate climate. I lit a fire.

Sounds ordinary, I know, but our species’ relationship with fire is rather exceptional. No other species controls fire the way humans do. There are some species that understand how useful fire can be, but they rely either on wildfires or fires lit by humans. Raptors form large congregations at active fire fronts to feast on the many animals that either attempt to flee the fire or were too slow and became a roast meal. The birds’ cunning exploitation of fire has led some to believe that certain Australian species actively spread fires by picking up embers and dropping them elsewhere. Impressive for sure, if true, but the birds still do not have the knowledge to make fire where first there was none. We do, and we alone. But we were certainly not the first in our long line of ancestors to make the most of fire.

Circumstantial evidence suggests that Homo erectus no longer exclusively chomped on raw food but ate food that had been cooked. And for cooking one needs fire. So far there is no evidence that Homo erectus had the knowledge to make fire. Most likely they managed to keep little fires going, harvested from wildfires, to start a proper fire when required. In which case, and I have no reason to doubt Homo erectus’ use of fire, human’s relationship with a volatile elemental force is old. About a million years old, give or take a few thousand years.

Cooking food is a major innovation. It makes food easier to digest and increases the absorption of some nutrients so increasing the total amount of nutrients that can be obtained from a meal. (Eating only raw food is thus an effective way to lose weight.) Homo erectus did not just chuck some roots and shoots on the fire. Our relatives had also developed into effective hunters so adding a regular roast to their diet. Combine cooking with meat-eating, and you have the perfect ingredients to grow that immensely expensive organ, the brain.

Fast forward a few hundred thousand years to our species, Homo sapiens, with an even bigger brain and the ability to make fire. Complete control over when and where to have a fire provided protection against cold and predators but also allowed Homo sapiens to change the landscape by burning.

I imagine the following scenario. Early humans realised that burned land is much easier to move through than a dense forest. At the same time, prey animals became easier to find, particularly if those were then attracted to the young shoots that would come up after the fire. The resulting ash fertilized the soil and so promoted the growth of edible plants. Even without the ability to control fire, early humans, including Homo erectus I’d imagine, benefitted from wildfires.

Imagine the power that the control of fire yielded early Homo sapiens. Now it was possible to burn areas at will instead of waiting for the next convenient lighting strike. Instead of seasonal wildfires, mainly towards the end of the dry season when the arrival of the wet season brought thunderstorms, fires could be lit at any time of the year, provided it wasn’t too wet. By using fire to manage the land, humans promoted the growth of vegetation at different stages in specific areas according to their needs. Such ‘pyrodiversity’ greatly increased the availability of both edible plants and prey animals through the generation of mosaic landscapes. Some animal and plant species were more resilient to human disturbances (more on that in later essays) so that both the diversity and abundance of species changed with increasing human impact.

Our species impact on the environment began way before we started to grow crops and burn coal.

Australia is one of the most fire prone countries on the planet, and bushfires continue to destroy property and kill people, either directly or due to smoke inhalation. It is thus not surprising that bush fire prevention is, pardon the pun, a hot topic. An argument that is often made is that fires were less severe when Indigenous peoples still practiced traditional burning¾firestick farming. By burning the land more regularly, there is less to burn, lower fuel load as they say, so that fires remained more controlled. Or so goes the argument. Some states are so wedded to the argument that they burn particular areas (certain national parks that should protect flora and fauna) so frequently that even the local fire-dependent flora does not have sufficient time to recover from the previous fire before the next one hits. But what is the evidence that fires were less impactful in the olden days?

It seems that at least in Africa, the cradle of humankind, fires had a much bigger impact between 4000 and 40,000 years ago than now. (Check out this paper if you want to know more: doi.org/10.1073/pnas.1118648109.) Before humans started to fragmentate the land through settlements and agriculture, fires could spread much further so that much more of the land would burn in a single fire event. In an ironic twist, it therefore appears that fire-related carbon emission through human-initiated fires, at least in Africa, were much higher thousands of years ago than they are now.

Across Australia, all states and territories currently have formal policies and legal frameworks governing burning, aimed both at reducing the risk of uncontrolled bushfires (hazard reduction) and at supporting cultural burning practices of Indigenous peoples. Implicitly, therefore, Australian fire management policy acknowledges that humans have had an impact on their environment for much longer than often assumed, way before agriculture and the industrial revolution.

There was never a time in which Homo sapiens did not have a significant impact on its environment. What has changed is the way we see that impact. As the 18^th century French philosopher Jean-Jacques Rousseau famously argued, humans are inherently good and pure “in a state of nature” but lost their innocence with the arrival of modern civilization. I don’t think that the many large animals that went extinct after the arrival of humans would agree.