New publication shows how overpopulation drives biodiversity loss

The concept of human overpopulation, once common, is now rarely used in the scientific literature. Yet overpopulation is a major driver of biodiversity loss and a key obstacle to fairly sharing habitat and resources with other species. A new publication from TOP explores the connections between human numbers and preserving wild nature.

by The Overpopulation Project

“Overpopulation is a major cause of biodiversity loss and smaller human populations are necessary to preserve what is left.” That’s the title of a new article by Phil, Pernilla and Frank just published in Biological Conservation. Those working to protect wild nature, including conservation scientists, rarely advocate for smaller human populations. Speaking out about population matters can be challenging; in fact, the journal’s editor has already fielded several complaints for publishing the article. But failure to address the root causes of biodiversity loss will doom conservationists’ efforts. Successfully protecting Earth’s remaining biodiversity requires challenging growth and reducing the excessive size of human populations and human economies, which are intimately connected.

Population has grown to almost 8 billion people. At the same time, the number of vertebrates that have gone extinct have followed a strikingly similar projection
As the human population has grown, so has the number of vertebrate extinctions. Graph from Population Matters.

Global biodiversity decline is best understood as too many people consuming and producing too much, thus displacing other species. Wild landscapes and seascapes are replaced with people, our livestock and crops, our economic support systems, and our trash. Conservation biologists standardly list five main direct drivers of biodiversity loss: habitat loss, overexploitation of species, pollution, invasive species, and climate change. All five direct drivers are important, on land and at sea. As we show in our article, all are made worse by larger and denser human populations.

Just as population increases clearly contribute to biodiversity losses, so population decreases aid in restoring biodiversity. All else being equal, smaller human numbers open more space for wild species. One sees this particularly clearly in Europe, densely populated, but also the first continent to end humanity’s modern population explosion. Europe’s overall population has stabilized in recent years and its rural population has declined 20% since 1960, contributing to extensive abandonment of less productive farmland. These trends have been valuable for wildlife, particularly larger herbivores and carnivores, which have naturally recolonized many former agricultural areas. Ecological restoration can accelerate these trends, turning what is often viewed as a negative (“rural depopulation”) into a positive (“rewilding” the landscape and restoring a country’s natural heritage). In certain habitats low-intensity traditional management is favorable for plants, insects and birds; such management should be encouraged as part of rewilding efforts, also creating jobs for people in rural areas.

Kulan is a subspecies of Asian wild ass that has been reintroduced to abandoned grassland in the Tarutino steppe, Ukraine. Photo: Michael Oppermann.

The article goes on to discuss opportunities for further research into how human demographic changes help or hinder conservation efforts. Most conservation biologists believe that greatly increasing the amount of land and seas in protected areas is necessary to preserve Earth’s remaining biodiversity. But the role of population reduction in achieving the goals of Half Earth or similar proposals remains largely unexplored. So does the role of population increase in closing off conservation options. How much of Germany or India, Mexico or New Zealand, would have to be set aside to preserve viable populations of their remaining native wildlife—and how large a human population would be compatible with this goal? How much of Africa’s megafauna can remain if the human population on the continent increases from 1.4 to 3.9 billion by 2100, as forecasted in the new United Nations population projections—and how much more could be saved if African nations provided their citizens with universal access to modern contraception and family planning services? For now, we can only guess at the answers. Conservation biologists could do better.

Finally, the article argues that scientists should advocate for smaller populations, explicitly, because current human numbers are far beyond what is compatible with the preservation of global biodiversity or long-term human wellbeing. In the long term, smaller human populations are necessary to preserve biodiversity in both less developed and more developed parts of the world. Whether the goal is to save threatened species, create more protected areas, restore degraded landscapes, limit climate disruption, or any of the other objectives key to preserving biodiversity, reducing the size of the human population is necessary to achieve it. According to recent United Nations projections, reducing fertility rates half a child below the projected medium (most likely) rate would reduce the global population in 2100 by more than three billion people. The benefits to other species certainly would be substantial.

The number of children people have should always be an informed personal choice. It is important that the decision is responsible, with respect to existing children, our communities, future generations, ecosystems, and wild species. If scientists are silent on this issue, parents (and governments) receive only the growthist propaganda of business lobbies. Fortunately, scientists have begun to speak up on the need for population reduction to achieve real ecological sustainability. Conservation biologists, motivated by love for the natural world, should lend their voices to those calls.

During the past hundred years, Homo sapiens‘ population increased from 2 billion to nearly 8 billion and the United Nations projects an increase to 10.4 billion before 2100, unless steps are taken to reduce this population growth. Ignoring the present high level and this projected increase means ignoring a major driver of the unfolding biodiversity crisis. Accepting current bloated human numbers as an appropriate status quo means accepting a biologically impoverished, and perhaps unlivable, planet. We must do better.


A letter by Green et al. criticizes our article and can be read here. Read also our reply to that critique.

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25 thoughts on “New publication shows how overpopulation drives biodiversity loss

  1. Overpopulation causing a loss of biodiversity is interesting, but in reality irrelevant. What is relevant is that overpopulation causing the extinction of humanity when wars are fought with weapons of mass destruction caused by the inability of the earth to supply the resources necessary was civilization to continue

  2. Hardly irrelevant. The cry Left right and centre, is that living space for all organisms is increasingly being squeezed.. It is not just economic issues that fan the drive for increased human growth, but includes masculinity, reliious and therefore power issues. The population avalanche must be slowed. The UN and family planning programs are the current most serviceable .institutions to try and address our potential environmental catastrophe, and this includes species extinction, pollution, food shortages and climate change..

  3. If we, the human race had any decent world-class leaders, one would expect a population fit to our current technology level, less crime, far better education, no religion (designed to enslave us), no pollution….. But we see the opposite. These people are not idiots. We are. Dumbed down relentlessly. Ergo: this mess is DELIBERATE.

  4. I’m totally with the authors. In Australia, the five yearly State of the Environment report was handed down yesterday and painted a dismal picture of biodiversity loss and decline. Interestingly, the report was unequivocal about population growth having a ‘very high impact’ on biodiversity. Sustainable Population Australia issued a media release which you can read here:

    1. This is interesting, because I was reading about that report on major mainstream media, waiting for the population issue to be at least mentioned, but nope. It was all “habitat destruction”, “sheep”, of course climate change… like those things just happen by themselves for some reason. Especially baffling is that no one explains that cities expand and habitats are destroyed because Australia has decided it wants to grow its human population for economic and power politics reasons.

    2. Thanks for sharing that. It’s a step in the right direction to acknowledge the role of population growth in driving biodiversity loss. Next up: making policy decisions that reflect that understanding.

      From SPA’s press release:

      The report says the biggest pressure on biodiversity is the clearing of native vegetation, the primary drivers of which are expansion of land dedicated mainly to agriculture and, to a lesser extent, forestry and infrastructure, including urban development.

      “The more people there are, the more land is cleared to grow food and fibre, as well as timber for shelter. Indeed, between 2000 and 2017, 7.7 million hectares of habitat for terrestrial threatened species was cleared or substantially degraded,” says Ms Goldie.

      Ms Goldie says any attempts to deal with the dire state of the Australian environment will be ineffectual if not accompanied by policies to stabilise and then reduce the size of the Australian population.

      “Whether Prime Minister Albanese goes for more population growth, or stops such growth for environmental protection reasons, is the test of his real commitment to the protection of Australia’s natural environment,” she says.

  5. Personally, I am against artificial rewilding. You cannot recreate an ecosystem that doesn’t exist anymore; much less so by bringing in just one or two big species and hoping everything else will follow. It’s just an example of human arrogance. We invest enormous resources in removing, sometimes cruelly, “invasive” species and bring back species we think ought to be there, forgetting that in nature everything changes all the time and that maybe some invasive species are better adapted than the species we choose according to our own standards.

    I think that nature does a much better job rewilding itself than we ever could. Just leave and watch what happens. Except that we always want to be in charge and “create jobs”, so we will not admit it.

    1. I see this as another complicate issue and one size does not fit all. It has been clearly shown rewilding can work if an area can be protected from human encroachment. Both the Nature Conservancy and National Geographic, among many, have shown protecting areas first and then bringing in species that formerly inhabited the areas does work. It is often not about just the single species but their introduction can help rebuild the natural flora and fauna.

      1. Could you give some examples? I’m not trying to argue, just curious.

        One of the problems is not just how to protect areas from human encroachment, but the other way round – what happens when species spill over from protected areas and cause problems to agriculture, etc? The problem is that it’s very hard to prevent herbivores from overbreeding and destroying everything when you cannot 1 hunt them 2 introduce predators that will kill livestock first

        With Covid we saw that a couple of weeks into lockdown or not even, there were dolphins swimming into cities, monkeys and goats hanging out on the roads, everyone all of the sudden heard the birds… I think rewilding should be like this: we won’t touch this area and we’ll see what happens, intervening only if there’s problems (to us, or animals are horribly starving and the like). I think we’d be pleasantly surprised.

    2. TOP has explored this issue in our series on Rewilding Success Stories (see under tab “Overpopulation”). It’s interesting; once you get into the details of projects, they always seem to be a mixture of consciously bringing back species and allowing nature to bring previously displaced species naturally.

      1. Thanks. I guess a lot depends on how you measure success, what the time frame is and most importantly who gets to decide what success is.

      2. An interesting article on one such project:
        I see several red flags here.

        I’ve seen similar projects in Italy and they often result in misery including for the animals involved. Maybe a counterexample, a successful reintroduction, could be the storks, although they seem to be able to return on their own without assistance, which is also my point 🙂

  6. Anyone seriously concerned about the state of our global environment cannot overlook the human overpopulation factor. The question I ask myself, why is it such a taboo subject when in earlier years it was widely discussed. Could it have something to do with cultural Marxism? After all, overpopulation, as in excessive birth rates, is not a problem in advanced countries, but in developing and emerging countries. The former just have a problem with immigration.

    1. It’s both sides. “A problem with immigration” means it’s totally taboo for most of the society, especially but not limited to the left; it’s “blaming the poor”, it gets you equated to fascists, etc.
      On the other side, big businesses, developers, even religious leaders all benefit from having more people to buy, consume, work, expand their power, so all they talk about is how we should have more people, not less.
      Also, decreasing the population forces you to make difficult but necessary decisions such as postponing the retirement age, an NO politician dares to do that.

      1. I agree with Gaia, the problem is across the political spectrum. The right wants more workers and consumers, so the economy can keep growing. The left wants more immigration, despite the fact that developed nations already have way more people than we can sustainably accommodate. And left, right and center all have a problem imagining economies that aren’t built around “more”

  7. The article is a great summary of all things concerning overpopulation and biodiversity loss, thanks a lot! I will propose to use this on the eurASP website, where we want to make an overview of all recent scientific publications concerning overpopulation.

    I sent the link of the full article to Center for Biological Diversity. Their ‘Endangered Specis Condoms’ are so important to raise awareness around it. I hope to have the European version soon, I can’t wait to hand them out here in Belgium, where high population density and increasing population is making nature protection impossible.

  8. The Fire Next Time is a 1963 non-fiction book by James Baldwin, containing two essays.
    The book’s title comes from a couplet in “Mary Don’t You Weep”, an African-American spiritual:
    “God gave Noah the rainbow sign
    No more water, the fire next time.”
    Baldwin did not understand the spiritual however – in the 20th century, no-one was reading the Bible properly, not even African-Americans. Many with political axes to grind were indeed misusing the Bible, or at least quoting it out of context, and they still do this.
    The real reason it is “the fire next time” is in 2 Peter 3. “But the day of the Lord will come like a thief. The heavens will disappear with a roar; the elements will be destroyed by fire, and the earth and everything done in it will be laid bare. …. That day will bring about the destruction of the heavens by fire, and the elements will melt in the heat. But in keeping with his promise we are looking forward to a new heaven and a new earth, where righteousness dwells.”
    This is looking a lot less fanciful now than at any time in the last 2000 years. However, it is probable that a Remnant of humanity will survive into the 22nd century, and let’s hope we don’t just start consuming ad infintum all over again ……… If the records of the Overpopulation Project are preserved, they could do much to prevent a “da capo al fine”.

  9. Continental Europe stabilised its population by sending vast numbers of its fertile people to England. Then they all try to go back on holiday on the same day and wonder why the whole south is gridlocked.

    Our universally environment hating politicians are in the process of removing protection from our top wildlife sites, now too. I never thought I’d live long enough to see the end of civilisation in the UK. Now it will happen any time there’s a coincidence of droughts in the countries that feed us.

    1. I’m pretty sure a lot of “native” Brits vacation in “Continental Europe” as soon as they get the chance. I know lots of Europeans have moved to the UK but many rich people from the UK have purchased expensive property all over Europe, including agricultural land in Eastern Europe, castles and estates in Tuscany… not to mention rich pensioners in Spain… It goes both ways.

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