Mammals cannot evolve fast enough to escape current extinction crisis

We humans are exterminating animal and plant species so quickly that nature's built-in defence mechanism, evolution, cannot keep up. An Aarhus-led research team calculated that if current conservation efforts are not improved, so many mammal species will become extinct during the next five decades that nature will need 3-5 million years to recover.

2018.10.15 | Peter F. Gammelby

[Translate to English:] Indri på Madagaskar er den største levende lemur. Den er også kritisk truet og meget evolutionært distinkt.

The secretive indri (Indri indri) of Madagascar is the largest living lemur. It is also critically endangered and highly evolutionarily distinct with no close relatives, a combination that makes its branch one of most precarious on the mammal evolutionary tree. In the likely event that the indri goes extinct, we will lose 19 million years of unique evolutionary history from the mammal tree of life. Photo:©pierivb,

En illustration af, hvordan de mindre pattedyr – her en sumpbæver (Nutria) – må udvikle sig og diversificere de næste 3-5 mio. år for at rette op på tabet af de store pattedyr. Grafik: Matt Davis, Aarhus Universitet.

An illustration of how smaller mammals - here exemplified by a nutria - will have to diversify for the next 3-5 million years to restore the loss of the large mammals. Graphics: Matt Davis, Aarhus Universitet.

Litopterner som denne Macrauchenia patachonica, der blev opdaget af Charles Darwin, var en mærkelig udseende gruppe af forhistoriske sydamerikanske pattedyr, der ikke var nært beslægtet med nogen levende arter i dag - de spaltede evolutionært fra andre pattedyr for over 65 millioner år siden.

Litopterns, like this Macrauchenia patachonica discovered by Charles Darwin, were a strange looking group of prehistoric South American mammals that were not closely related to any species alive today–they diverged evolutionarily from other mammals over 65 million years ago. When they went extinct at the end of the Ice Age, the mammal Tree of Life lost one of its deepest branches. Illustration:Bruce Horsfall, Macmillan, New York. Via Wikimedia Commons

There have been five upheavals over the past 450 million years when the environment on our planet has changed so dramatically that the majority of Earth’s plant and animal species became extinct. After each mass extinction, evolution has slowly filled in the gaps with new species.

The sixth mass extinction is happening now, but this time the extinctions are not being caused by natural disasters; they are the work of humans. A team of researchers from Aarhus University and the University of Gothenburg has calculated that the extinctions are moving too rapidly for evolution to keep up.

PNAS is an abbreviation for Proceedings of the National Academy of Sciences of the United States of America.

If mammals diversify at their normal rates, it will still take them 5-7 million years to restore biodiversity to its level before modern humans evolved, and 3-5 million years just to reach current biodiversity levels, according to the analysis, which was published recently in the prestigious scientific journal, PNAS.

Some species are more distinct than others

The researchers used their extensive database of mammals, which includes not only species that still exist, but also the hundreds of species that lived in the recent past and became extinct as Homo sapiens spread across the globe. This meant that the researchers could study the full impact of our species on other mammals.

However, not all species have the same significance. Some extinct animals, such as the Australian leopard-like marsupial lion Thylacoleo, or the strange South American Macrauchenia (imagine a lama with an elephant trunk) were evolutionary distinct lineages and had only few close relatives. When these animals became extinct, they took whole branches of the evolutionary tree of life with them. We not only lost these species, we also lost the unique ecological functions and the millions of years of evolutionary history they represented.

"Large mammals, or megafauna, such as giant sloths and sabre-toothed tigers, which became extinct about 10,000 years ago, were highly evolutionarily distinct. Since they had few close relatives, their extinctions meant that entire branches of Earth's evolutionary tree were chopped off” says palaeontologist Matt Davis from Aarhus University, who led the study. And he adds:

"There are hundreds of species of shrew, so they can weather a few extinctions. There were only four species of sabre-toothed tiger; they all went extinct."

Long waits for replacement rhinos

Regenerating 2.5 billion years of evolutionary history is hard enough, but today’s mammals are also facing increasing rates of extinction. Critically endangered species such as the black rhino are at high risk of becoming extinct within the next 50 years. Asian elephants, one of only two surviving species of a once mighty mammalian order that included mammoths and mastodons, have less than a 33 percent chance of surviving past this century.

The researchers incorporated these expected extinctions in their calculations of lost evolutionary history and asked themselves: Can existing mammals naturally regenerate this lost biodiversity?

Using powerful computers, advanced evolutionary simulations and comprehensive data about evolutionary relationships and body sizes of existing and extinct mammals, the researchers were able to quantify how much evolutionary time would be lost from past and potential future extinctions as well as how long recovery would take.

The researchers came up with a best-case scenario of the future, where humans have stopped destroying habitats and eradicating species, reducing extinction rates to the low background levels seen in fossils. However, even with this overly optimistic scenario, it will take mammals 3-5 million years just to diversify enough to regenerate the branches of the evolutionary tree that they are expected to lose over the next 50 years. It will take more than 5 million years to regenerate what was lost from giant Ice Age species.

Prioritizing conservation work

"Although we once lived in a world of giants: giant beavers, giant armadillos, giant deer, etc., we now live in a world that is becoming increasingly impoverished of large wild mammalian species. The few remaining giants, such as rhinos and elephants, are in danger of being wiped out very rapidly," says Professor Jens-Christian Svenning from Aarhus University, who heads a large research program on megafauna, which includes the study.

The research team doesn’t have only bad news, however. Their data and methods could be used to quickly identify endangered, evolutionarily distinct species, so that we can prioritise conservation efforts, and focus on avoiding the most serious extinctions.

As Matt Davis says: “It is much easier to save biodiversity now than to re-evolve it later.”



Professor Jens-Christian Svenning
Mobil: +45 2899 2304

Postdoc Matt Davis
Mobil: +45 20 59 99 67    


Matt Davis is part of the Carlsberg Foundation's Semper Ardens project "Megafauna Ecosystem Ecology from the Deep Prehistory to a Human-Dominated Future" and the Centre for Biodiversity in A Changing World (BIOCHANGE) at the Department of Bioscience at Aarhus University, both headed by Professor Jens-Christian Svenning. The third member of the group is Søren Faurby from Gothenburg University.

Read the article "Mammal diversity will take millions of years to recover from the current biodiversity crisis" in PNAS

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Tags: Miljø, pattedyr, den sjette masseuddøen, evolution