Prehistoric man changed the environment

Humanity altering the environment seems to be a very topical issue. The news seems to be full of stories about another animal we’ve driven extinct, another river we’ve polluted and how we’ve doomed our planet through man-made global warming.

On the other hand we think of hunter-gatherers as living a much more balanced life, in tune with nature. They move around frequently so as not to irrevocably deplete on region, taking only what they need before moving on. Harming the environment seems to be the preserve of “modern” man and his evil industrialised society.

Even their weaponry is made of renewable resources!

However, this dichotomy is a romanticism, with people looking back at tribal life through rose-tinted glasses. In reality hunter-gatherers can drastically alter the environment in which they live.

Indeed, humanity has spent most of its (pre)history surviving off the land and during that time we’ve managed to considerably change the planet.

Between ~50,000 years ago and 10,000 years ago, back when Homo sapiens was first leaving Africa as a tribal species, ~80% of large animals went extinct. The closest I’ve ever come to doing primary research was to show there is a strong correlation between when humans first arrived in an area and when the animals in that region went extinct.

As innocent, “natural,” hunter-gatherers it would seem our species was the primary reason mammoths, along with many other animals, went extinct and the fauna of Australia was decimated with nearly every species weighing over 100kg being wiped out.

Our ancestors didn't have the same understanding of awesomeness we do.

New research has further undermined the notion that our hunter-gatherer ancestors lived “in balance” with the environment by showing they influenced the very environmental cycles themselves – namely fire regimes.

Fire has a drastic effect on the environment, altering how animals and plants behave. In particular there are some species of plant which require fire to act as an external stimulus that prompts their seeds to grow. Thus what time of the year most fire happens has an impact on the environment.

This research modelled the relationship between the likelihood a region next to a fire is flammable, the likelihood it will spread to that adjacent region and the number of times a fire is started.

For example, in a Savannah environment during the dry season there is a lot of dry vegetation around so the likelihood a region next to a fire is flammable is rather high. Since there are few gaps in this vegetation, the chance of the fire spreading is also rather high. Thus not many fires have to be started for devastation to occur.

I love the smell of statistical modelling in the morning

However, other environments with more gaps between vegetation, such as woodland, wouldn’t be as easily devastated by a limited number of ignition events. But if humans artificially inflated the number of fires by…well, making fires, then there would be more woodland devastation.

And if human ignition became the primary source of fire – both in woodland and in other environments – then they would start occurring all year round rather than just in the wet season when lightning – the previous source of ignition – was present. Such a change in timing would likely alter the very environment itself.

So they looked at the archaeological record to see when humans starting making sufficient fires to cross this threshold and found it would happen around 40,000 years ago.

Before humans had even arrived in Europe*, we were changing the very environmental cycles of Africa itself.

Table A shows in a low connected environment (i.e. woodland) then humans would increase the area burned by stage 4 (~40 kya). Table B shows as soon as humans started making fire (stage 3) more would be burned during the dry season in all environments.

But before one gets carried away expounding the evils of man, it’s worth noting the study has a few flaws. Firstly, most early evidence for fire is highly circumstantial, amounting to a few splodges of charcoal here and there. As such, the timeline they’ve created for when humans would start making enough fire to influence the environment is likely far from accurate, although the general trend probably is true.

Secondly, since this is a model it requires a particular scenario to occur before it can play out – namely humans making more fire in a wooded environment. To my knowledge there is no evidence this actually happened meaning all this paper can really say is there is a possibility humans would influence fire regimes, provided they behaved in a certain way.

And to me, that introduces too many qualifiers into the conclusion for it to be of much use. Sure its interesting to note that there is this possibility, but until that’s show to be an actuality then there’s not much we can really take away from this paper.

Archibald S, Staver AC, & Levin SA (2011). Evolution of human-driven fire regimes in Africa. Proceedings of the National Academy of Sciences of the United States of America PMID: 22184249

*The first definite evidence of human habitation in Europe is the Aurignacian industry (the language boundaries of which I’ve talked about before) that started ~35 kya. There were Upper Palaeolithic industries prior to this, but they were sporadic and may have been made by neanderthals. However, it is still possible humans made them and they were actually in Europe potentially as early as 50 kya.