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Human activities threaten billions of years of unique evolutionary history

By on May 26, 2020 in Amphibians, EDGE Amphibians, EDGE birds, EDGE Mammals, EDGE Reptiles, Mammals, News, Reptiles

Natural ecosystems across planet Earth are experiencing unprecedented losses of biodiversity due to human activities, yet the distribution and intensity of these activities are not uniform across the Earth’s surface. In our research, published in Nature Communications, we explored how human activities are impacting the world’s most unique biodiversity to identify regions and species of critical importance for conservation efforts.

In its purest sense, biodiversity is living variation – the differences amongst and within individuals and species, their genes and traits, and the ecosystems they comprise. One measure of biodiversity is the amount of evolutionary history—the branches of the tree of life—represented by a single species or sets of closely related species. Each branch has a length, measured in millions of years, and we can count these branch lengths to quantify uniqueness of, and variation between, species. This biodiversity measure, known as ‘Phylogenetic Diversity’, underpins our work at the EDGE of Existence programme, and we used the measure to quantify biodiversity for this study.


Where in the world?

First, we mapped the evolutionary history of the world’s reptiles. “Why reptiles?” I hear you ask. For three very important reasons: 1) the global distribution of reptilian evolutionary history remains largely unexplored, 2) reptiles are more evolutionary diverse than amphibians, birds and mammals (full disclosure: we discovered this after we ran the analyses!), and 3), reptiles have received very little conservation attention, compared with birds and mammals (and even amphibians) in the past.

The range size of the world's lizards, snakes, amphisbaenians and the tuatara
The tree of life for lepidosaurs (lizards, snakes and the Tuatara), with branches coloured by range size of each species. Adapted from Gumbs et al. 2020, Nature Communications, available at: under the creative commons attribution 4.0 license:


Our aim was to identify regions of the planet with large concentrations of unique evolutionary history restricted to very small areas of the planet. These areas are incredibly important to conserve to prevent the extinction of unique species and the loss of their branches of the tree of life forever. To do this, we mapped the tree of life for the world’s reptiles, with the length of each branch being spread evenly across all roughly 100 km grid cells in which species that evolved along that branch are known to occur. Areas where many branches of the tree of life overlap and are spread across very few grid cells accumulate large amounts of evolutionary history – these branches (and their descendant species) are found pretty much nowhere else on Earth. This method, known as ‘Phylogenetic Endemism’, has been around for more than a decade. Not very groundbreaking (so far).

To explore how human activities overlap with the highest concentrations of unique and endemic (restricted to small areas) evolutionary history, we intersected the top 10% of grid cells with the greatest concentrations of evolutionary history with human pressure information from the Human Footprint dataset. We were distressed—though not entirely surprised—to discover that almost three quarters of the planet’s most irreplaceable regions for reptilian evolutionary history are found in areas under high or very high human pressure. This is a significantly higher overlap than we would expect if human pressure was distributed at random across the planet. Equally disconcerting is the fact that just 5% of these grid cells are experiencing low or no human pressure, significantly lower than we would expect.

Adapted from Gumbs et al. 2020, Nature Communications, available at: under the creative commons attribution 4.0 license:
The overlap of human pressure and the most important regions for evolutionary history of reptiles, globally. Grid cell colours indicate the level of human pressure and are restricted to the regions with the greatest concentrations of unique and endemic evolutionary history. Adapted from Gumbs et al. 2020, Nature Communications, available at:


Given the alarmingly high overlap of intense human pressure and irreplaceable reptilian evolutionary history, we incorporated human pressure data directly into our mapping of evolutionary history. Rather than spreading the branches of the tree of life evenly across the grid cells they occur in, our new metric, ‘Human-Impacted Phylogenetic Endemism’ or HIPE (which also describes your current emotional state reading this, right?), spreads the branches in relation to human pressure. High human pressure grid cells receive a smaller proportion of a branch than grid cells experiencing lower human pressure, under the reasonable assumption that high pressure regions have smaller areas of suitable habitat remaining compared with low pressure regions.

As conservationists, we are particularly keen to identify the areas of the planet most in need of urgent action. Using our HIPE metric we were also able to identify regions where large concentrations of unique and endemic evolutionary history are almost wholly restricted to grid cells under intense human pressure. These regions have no neighbouring areas of low human pressure to safeguard the future of their endemic biodiversity. When we mapped this for the world’s reptiles our findings were again rather alarming. Large amounts of unique evolutionary history are endemic to regions under intense human pressure, particularly across the Western Ghats of India, Sri Lanka, the Caribbean and the Philippines, with very little in the way of sanctuary in regions of lower human pressure.

Regions of the planet where unique and endemic evolutionary history is restricted to grid cells under intense human pressure. Darkest red grid cells have the greatest proportions of their evolutionary history found only in regions under very high human pressure. Adapted from Gumbs et al. 2020, Nature Communications, available at:


Of course, as we mapped our reptile biodiversity using almost 100 km grid cells, there are likely to be small areas within grid cells under intense human pressure, such as protected areas, that represent hope for those unique species persisting in highly impacted environments. However, when we explored the human pressure at a much finer scale across regions under very high human pressures, we found that very few, if any, grid cells had any significant amounts of pristine habitat remaining. Clearly, we must focus on identifying pathways to maintaining and restoring biodiversity in these heavily impacted areas of the planet.

After developing our HIPE method using reptiles, we then extended our analyses to include all other terrestrial vertebrates, too: amphibians, birds and mammals. We found that, on average, reptiles have greater concentrations of unique and endemic evolutionary history than any other group, closely followed by birds. We also found that reptiles tend to contribute the most biodiversity, relative to other terrestrial vertebrates, in the more arid regions of the Middle East, North Africa and the Namibian coast of southern Africa. When we mapped HIPE for all groups combined, we found Madagascar, the Western Ghats, large parts of Central and South America and Southeast Asia, the Caribbean, Central and East Africa, and Australia, are highlighted as harbouring the highest concentrations of unique and endemic evolutionary history.

Global distribution of the unique and endemic evolutionary history of terrestrial vertebrates. Red grid cells have the highest concentrations of endemic biodiversity, whereas blue have the lowest. Adapted from Gumbs et al. 2020, Nature Communications, available at:


Identifying priority species

Next, we explored how human activities threaten the terrestrial vertebrate tree of life at the species level. We used extinction risk data for roughly 25,000 species of amphibians, birds, mammals and reptiles and calculated the amount of evolutionary history currently at risk of extinction due to human activities. We found that close to 50 billion years of unique evolutionary history is under threat. Reptiles alone stand to lose at least 13 billion years of evolutionary history, more than all birds and mammals combined. Unsurprisingly, given the precipitous global decline of amphibians, more than 20 billion years of amphibian evolutionary history is also at risk of being lost. The scale of these numbers is incomprehensible: we face the loss of more years of evolutionary history than there have been years since the beginning of the Universe!

Each species on the tree of life sits atop its own unique branch, a branch shared with no other species. The length of this branch, known as the ‘terminal branch’, represents the amount of unique evolutionary history for which each species is currently responsible. We used this measure of uniqueness, in combination with the human pressure across a species’ global distribution, to identify species that embody large amounts of unique evolutionary history that are endemic to areas under the greatest human pressure. We found that amphibians and lizards are particularly unique and restricted to high pressure regions, whereas birds and mammals are more widely distributed and less unique.

From Gumbs et al. 2020, Nature Communications, available at: under the creative commons attribution 4.0 license:
The ‘HITE’ scores of the world’s terrestrial vertebrates – HITE measures the evolutionary uniqueness of a species and the level of human pressure present across its distribution. Panel a: amphibians have the greatest HITE scores of terrestrial vertebrates. Panel b: Data Deficient (DD) species are comparable in their HITE scores to the most threatened species, which are Endangered (EN) and Critically Endangered (CR) on the IUCN Red List. Panel c: Amphibians, lizards and snakes that are DD also have higher HITE scores than DD turtles, birds and mammals. Adapted from Gumbs et al. 2020, Nature Communications, available at:


Worryingly, we also found that species with Data Deficient IUCN Red List assessments—predominantly reptiles and amphibians—are comparable in both their evolutionary uniqueness and exposure to intense human pressure to threatened species. This suggests many species for which we currently lack sufficient understanding of their conservation status may be at acute risk of extinction, and warrant urgent conservation attention.

To help direct conservation efforts, we highlighted a number of priority species that are highly evolutionarily unique and restricted to regions under intense human pressure. Some of the priority species that are also currently known to be threatened with extinction are priority EDGE Species, the most unique and threatened species on the planet, such as the Mary River Turtle (Elusor macrurus), the Purple Frog (Nasikabatrachus sahyadrensis), the Numbat (Myrmecobius fasciatus), and the Tokashiki Gecko (Goniurosaurus kuroiwae).

©Shawn Miller<br /><br /> Please contact the photographer directly if you would like to use this picture.
Many priority species identified in the study are also priority EDGE species, such as the Tokashiki Gecko (Goniurosaurus kuroiwae).


In addition, many of the species identified as priorities for urgent research are very poorly known, with some having not been seen for decades. Indeed, twelve of the twenty priority lizards and snakes are Data Deficient on the IUCN Red List, and these twelve species alone embody more than 500 million years of evolutionary history. These are some of the most unique animals on the planet, from burrowing lizards with rudimentary legs and thread-like blind snakes to pink worm-like amphibians called caecilians and even a golden mole known only from remains found in a single Barn Owl pellet in Somalia in the 1960s.

The egg of the highest priority amphibian identified in the study, the caecilian Chikila fulleri.


We are still learning the true extent to which human activities are encroaching on our natural habitats and threatening our most unique and important biodiversity. Our findings indicate that the magnitude of our impact as a species on the natural world is incomprehensibly large, and appears to be overwhelmingly impacting the most irreplaceable areas and species on the planet.

However, our work also shows us that it is not too late to change the course we are on to avoid even greater impacts. On the ground conservation efforts to conserve the some of the most unique and threatened species, such as those efforts by the EDGE of Existence programme, are already underway, and evidence suggests that even small increases in the global protected area network can lead to huge gains in conservation impact. If we can work together to reduce our impacts on the natural world and conserve our natural habitats and species, we have the opportunity to avert the loss of an incredible amount of irreplaceable biodiversity.

Mount Bamboutos