Earth would obviously be a different place without humans. But aside from the lack of cities, farmland and cat videos, it might also be teeming with an exotic array of large mammals, according to a new study. Even Europe and the Americas might host enough supersized wildlife to rival the famous megafauna of sub-Saharan Africa.
"Most safaris today take place in Africa, but under natural circumstances, as many or even more large animals would no doubt have existed in other places," lead author Søren Faurby, a biologist at Denmark's Aarhus University, says in a statement. "The reason that many safaris target Africa is not because the continent is naturally abnormally rich in species of mammals. Instead it reflects that it's one of the only places where human activities have not yet wiped out most of the large animals."
Along with fellow Aarhus biologist Jens-Christian Svenning, Faurby has produced the first global map of mammal diversity on a hypothetical Earth without human influence. Here it is, color-coded to show the number of large mammal species — those weighing at least 45 kilograms, or 99 pounds — native to a given area:
The estimated diversity of large mammals if humans hadn't spread around the planet. (Illustration: Søren Faurby)
And here's what the current diversity of large mammals looks like:
Earth's remaining enclaves for large-mammal diversity are in Africa and on mountain ranges. (Illustration: Søren Faurby)
In a previous study, Faurby and Svenning refuted the idea that natural climate change was primarily responsible for wiping out megafauna like mammoths, woolly rhinos, sabre-toothed cats and giant sloths, reporting a stronger correlation with the arrival of humans to their habitat. And for the new study, they examined the natural ranges of 5,747 mammal species to map their diversity patterns "as they could have been today in the complete absence of human influence through time."
(As Faurby adds, this doesn't necessarily assume humans never existed: "[W]e are actually modeling a world where modern humans never left Africa and where they did not influence the distribution of any mammalian species but themselves.")
Their map shows the richest variety in the Americas, especially what's now Texas, the U.S. Great Plains, southern Brazil and northern Argentina. That's partly because the Americas were home to 105 of the 177 large-mammal species that vanished between 132,000 and 1,000 years ago, a collapse the researchers blame mainly on hunting (of the animals themselves or their prey). But American mammals wouldn't be the only beneficiaries of an unpeopled planet — animals like elephants and rhinos would roam Northern Europe, for example, and the diversity of megafauna would also roughly double in Africa, India, Southeast Asia and parts of Australia.
Today, such hotspots are largely limited to Africa and various mountain ranges around the world. Africa's remaining biodiversity may seem odd since humans evolved there, but the researchers cite several factors that may have helped its megafauna survive, including "evolutionary adaptation of large mammals to humans as well as greater pest pressure on human populations." As for mountains, the terrain has helped buffer mammals from human hunters and habitat loss.
"The current high level of biodiversity in mountainous areas is partly due to the fact that the mountains have acted as a refuge for species in relation to hunting and habitat destruction, rather than being a purely natural pattern," Faurby says. "An example in Europe is the brown bear, which now virtually only lives in mountainous regions because it has been exterminated from the more accessible and most often more densely populated lowland areas."
The human-free map is speculative, of course, portraying a world where our absence is the only variable. While research does suggest humans were the main culprits in megafauna extinctions, Faurby says the new map excludes other factors for simplicity. "We are assuming that humans were involved in all extinctions within the last 130,000 years," he writes in an email, "and that none of them were natural phenomena as a consequence of e.g. competition or climate change."
"This is unlikely to be completely true," he acknowledges, "but accumulating evidence exists for human involvement in a vast majority of the extinctions, and this assumption is therefore likely unproblematical."
Despite the implication that a world without humans would be ecologically healthier, Faurby says the study is not meant to be misanthropic. Humans are its target audience, and he hopes visualizing the loss of biodiversity like this can help inspire modern humans to learn from the mistakes of our ancestors.
"I do not see our results as necessarily a doom scenario," Faurby writes. "I would rather see it as suggesting the magnitude of effects without an active conservation community. Humans and large animals can co-occur, but unless there are cultural, religious or legal rules in place to protect the animals, many large animals will often disappear from areas under strong human influence."
Svenning agrees, pointing out that embattled mammals like wolves and beavers have begun to claw back in some parts of the world. "Especially in Europe and North America, we see many large animal species making remarkable comebacks, doing better than they have for centuries or millennia," he writes. "At the same time, much of the rest of the world continues to undergo defaunation, especially losing the larger species. Hence, modern societies can develop so as to provide better possibilities for human-wildlife coexistence than in historical societies, but whether this happens depends on the socioeconomic and, perhaps, cultural circumstances."