Prehistoric man changed the environment

ResearchBlogging.orgHumanity 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.


15 thoughts on “Prehistoric man changed the environment

  1. I would be interested to see a definition of each stage of human evolution.

    Anyway in terms of extinction: When any new species enters a food chain there is a massive overhaul in that ecosystems balance, and that is if only one food chain is disturbed. As humans we tend to enter several food chains and often at several stages of it so I wouldn’t be surprised if we were disrupting nature in that way. I suppose as we multiplied and spread to so many other areas that could cause some extinction. Environmental manipulation would make the matter much worse.

    But even if this paper was 100% accurate in its methods, I would have trouble believing that the state of disruption we caused 40 kya is the same as or near to what we cause today…

    • Indeed, we’re doing more damage than our species used to, but it should be remembered that we did still cause damage in the past as well. Viewing tribal societies as somehow neutral or in tune with the environment is just wrong.

      As for the stages, 1=bipedalism, 2=first use of natural fire, 3=creation of fire, 4=human dispersal around the globe, 5=advent of agriculture.

      • Changing the environment is not the same thing as damaging the environment. As you say, we do a lot more actual ‘damage’ to the environment now than at any other time in human history. In the Pleistocene, there were no toxic mine tailing ponds, moonscapes, dioxins, strontium 90, diverted rivers, drained lakes, massive dams, vast tracts of clearcut forest, DDT, mercury contaminated fish, depleted uranium or atomic bomb testing, holes in the ozone, etc.
        So when most people talk about hunter gatherers living in harmony with the nature I always take it they are talking in relative terms, not some absolute harmony (since no creature lives in absolute harmony).

      • At the same time, our hunter-gatherer ancestors did drive many species to extinction and often devastated environments they entered. Even taking into account the fact hunter-gatherers don’t live in perfect harmony with nature, most people still underestimate the influence supposedly “natural” lifestyles can have on the environment.

        • “At the same time, our hunter-gatherer ancestors did drive many species to extinction”

          This hypothesis is highly contested and mostly based on circumstantial and indirect evidence. The strongest evidence for this is only found for island habitats.

          “and often devastated environments they entered”

          Which environments did they “devastate”?

      • Many people do overstate the effect humans had on animal life during the end of the Pleistocene, often missing the fact that human migration was enabled (and so occurred at the same time as) climate change; making it difficult to disentangle the two effects.

        However, that doesn’t mean humans didn’t play a role in these extinctions and there are many cases where it seems apparent we did. Often these extinctions were very harmful for ecosystems as they were “keystone” species.

        Perhaps the most apparent and most devastating case of hunter-gatheresr driving animals extinct occurred when we first migrated into Australia. This was because these first inhabitants appear to have “fired” the landscape, starting bushfires to promote the growth of new vegetation they can eat. This, combined with intensive hunting, fundamentally altered Australia’s ecosystem. Further, this coincided with a period of modest climate change, so that was likely not a factor.

        • Actually Australia is a weak example of human-caused extinctions due to the paucity of sites that have been studied dating beyond human arrival. There is very little evidence that humans even co-existed with extinct species because most of them went extinct before human arrival. (Judith Field and Stephen Wroe, 2012 .World Archeology, Vol. 44, issue 1.)The Paleoclimate data seems to indicate a long trend of steady aridification of the continent over hundreds of thousands of years. Humans did fire the landscape, but this mostly favored the growth of certain vegetation, and with it, game animals. Some anthropologists have even called this ‘fire-stick farming’. I’m not sure if increasing the growth of some kinds of vegetation would be an apt description of ‘devastating’ the environment.

  2. I do find the public’s opinion of cavemen very odd. On the one hand they have the perfect diet and are in tune with nature as you put it.

    On the other hand they are illiterate unsocial animals who live in caves.

    In my opinion they were probably just human, like we are now (without all these laptops and the like). We played games, we talked about the weather (once they got to the UK that would be certain fact), we had relationships and communities. Some would want more power than others, others would just want to do what’s best for everyone. So on and so forth. Anyway I’m rambling now so I’ll stop.

    • Well people did use to think of them as savage brutes and this “in tune with nature” thing arose partly as a response to that idea. So you’ll have some people sticking with the typical view and some with the counter-culture.

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    • Neanderthals didn’t evolve into modern humans, instead they are a cousin to our species. We shared a common ancestor between 500-600 thousand years ago, but since then went down our different paths.

      Are they mentioned in the Bible? I do not know since scripture doesn’t used taxonomical names (it would be easier if one could just search for the word neanderthals) but it is unlikely they are in there under a different name given the difference between the Bible being written and the neadnerthals dying out is at best ~20 thousand years.

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