The planet is currently undergoing its sixth mass extinction, but it’s not just individual species being wiped out. A new study has found that human activity is responsible for eliminating entire groups of species, in what researchers are calling a “mutilation of the tree of life”.
The Tasmanian tiger, Yangtze River dolphin, and passenger pigeon are some of the most recent species to become extinct – but they were also the last members of their genera, the taxonomic rank above species in biological classification.
A human-made dent in our planet
Scientists from Stanford University and the National Autonomous University of Mexico have discovered that this is reflective of a much deeper crisis. Out of 5,400 genera of land-dwelling vertebrate animals examined (including 34,600 species), 73 have gone extinct since 1500 CE, and the current rate of genus extinction is 35 times greater than that of the last million years.
The study also found that, without human influence, most likely only two genera would’ve been lost in the same amount of time. Instead, they argued that humans had caused a “biological annihilation” over the last 500 years.
Whilst this language might seem strong, the researchers believe, given the gravity of their findings, that it’s more than appropriate.
“As scientists, we have to be careful not to be alarmist,” Ceballos explained, but said it would “be unethical not to explain the magnitude of the problem, since we and other scientists are alarmed.”
Taking an axe to the tree of life
Imagine, if you will, a single species as a twig on the tree of life. If that twig is cut off, nearby twigs (aka species in the same genus), can quickly grow to fill in the gaps – in other words, closely related species can help, at least partly, to take over lost species’ roles within an ecosystem.
However, when a whole branch (genus), is lopped off, it can be much more difficult for the ecosystem to recover; the paper explains that it can take millions of years for the process of evolution to generate a suitable replacement. In the meantime, there can be significant impacts on both an ecosystem’s stability and human life.
“This mass extinction is transforming the whole biosphere, possibly into a state in which it may be impossible for our current civilization to persist,” the authors wrote in their paper.
In the study, the researchers provide the example of the passenger pigeon; it once competed with the white-footed mouse, a carrier of the bacteria that cause Lyme disease, for food. After the extinction of the pigeons, the mouse population boomed, and with it, the incidence of Lyme disease in humans.
They also argue that the mass elimination of entire genera could contribute to the climate crisis.
“Climate disruption is accelerating extinction, and extinction is interacting with the climate, because the nature of the plants, animals, and microbes on the planet is one of the big determinants of what kind of climate we have,” explained Paul Ehrlich, the study’s other author.
Immediate action required
“Today there is a species [humans] that should know it is not able to wait millions of years for its life-support systems to be restored after a mass extinction,” states the study’s conclusion, calling to action political, economic, and social movements to prevent any further extinction.
It highlights a particularly immediate need for action in the tropics of the Americas, Asia, and Africa, with these areas experiencing the highest concentration of both genus extinctions and genera with only one remaining species.
The authors also think that tackling population growth and, consequently, an increase in consumption is an important factor in this.
“The idea that you can continue those things and save biodiversity is insane,” Ehrlich. “It’s like sitting on a limb and sawing it off at the same time.”
And let’s be honest, that doesn’t sound very fun.
The study is published in the Proceedings of the National Academy of Sciences.