Biological mass extinction far more serious than previously thought?


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The world’s biosphere could be likened to a great wall, the human perched atop it. And if the biosphere were to lose a few species of animals, the wall would only lose a few bricks and still remain standing. But soon, if more and more animals go extinct, the entire wall may, just may, come crumbling down. The question is who is removing the bricks?

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– Does the tempest halt for the sake of your blindness?
From the poem Utpakhi (The Ostrich); Dutta, Sudhindranath

Source: Wikimedia Commons

A mass extinction episode is a global phenomenon during which more than seventy-five percent of Earth’s wildlife goes extinct. And, over the last half a billion years, five such mass extinction episodes have decimated Earth’s wildlife. The most recent being the one that wiped out dinosaurs forever. But how many of us are aware that several recent research studies1,2 have time and again claimed that Earth is in the throes of yet another mass extinction episode: the sixth mass extinction.

Indeed, over the last 100 years, 200 species of vertebrates have gone extinct3. This extinction rate, of two species a year, may only elicit a shrug of your shoulders and may not sound alarming: Animals go extinct all the time, such is the way of nature. But when one considers the rate at which animals usually went extinct in the last two million years, two hundred species would not have taken a hundred years but ten thousand years to go extinct.

The extinction rate, in other words, has risen drastically – by almost 100 times – as compared with the eras before and in too short a window of time, the last one hundred years.

A research article3, published recently in the journal PNAS [Proceedings of the National Academy of Sciences], however, goes one step further with its claims regarding the sixth mass extinction.

This study reports that not only is the unsheathing of the sixth mass extinction a contemporary phenomenon, but it is also a lot more severe in magnitude than previously thought. Furthermore, this study also alludes to the fact the human animal seems to be solely responsible for this one. It is interesting to note that even the first mass extinction, which occurred much, much before the first human being came into existence, was caused not by a shower of meteors or by great volcanic eruptions but by animals8.

“In the last few decades, habitat loss, overexploitation, invasive organisms, pollution, toxification, and more recently climate disruption, as well as the interactions among these factors, have led to catastrophic declines in both the numbers and sizes of populations of both common and rare vertebrate species,”3 write the authors – Gerardo Ceballos, Paul R. Ehrlich, Rodolfo Dirzo – in their research article. Furthermore, according to the study, in the last hundred years, “50% of the number of vertebrate individuals that once shared Earth with us3 have already been wiped out”, and such a catastrophic decline of animal populations thus indicates that the sixth mass extinction is already under way.

But why should we, as humans, care even if we lost more than 75% of our animals through mass extinction? Because given how interdependent different animals are in the ecosystem web – Domino Collapse – even humans would be adversely affected.

Take insects, for example. If tens of thousands of species of insects go extinct before the environment can adapt to their absence, then thousands of species of trees too would disappear as many species of trees are dependent on insects for pollination. And if trees disappear, the death knell would be all but sounded for the human race.5 Our air would be filthy, toxic, and the ambient temperature of the Earth would rise by several degrees. The rate of soil degradation would rise, and so will the rate of soil erosion resulting in the loss of arable land. Rainfall would be seriously affected, and in turn, so would be the quality of our freshwater sources. The human animal, assuredly, would be negatively hit.

Therefore, given that this mass extinction could prove to be a credible threat to human survival, it is rather discomfiting to realize that we – the primary reason behind this extinction episode – appear to be blind to it. Two reasons explain why?

The first reason: The two species that disappear every year are ones that either are not alluring enough for us [not as alluring as the lion, for example] or live in isolated corners of the world, and, hence, we never really feel their loss.

For instance, do you know of the Catarina Pupfish? Or of the Christmas Island Pipistrelle? The Pyrenean Ibex? All three disappeared for good in the recent past, but how many of us are aware of this fact.

The second reason that contributes to our not being fully informed of the threat of mass extinction is that previous research studies have focused strongly only on the ‘end point’ – the complete extinction of animal species – to deduce the health of Earth’s wildlife. And this approach, the study in question highlights, is the fundamental reason why previous studies have underestimated the magnitude of the present mass extinction. The following paragraphs explain this in greater detail.

Consider, for the sake of argument, an animal species ‘X’. This animal X is spread across fifteen different countries in Asia. This animal’s ‘global population’, in other words, comprises ‘local populations’ spread across fifteen different countries. There would be one local population, of a certain number of individuals, of animal X in one country; another local population, of a certain number of individuals, in another country, and so on.

Suppose, after a year, we observe that out of the fifteen local populations, fourteen have been wiped out – local population extinctions – and only one last local population exists.

In such a scenario, if we were to concentrate only on the ‘end point’ – the complete extinction of this animal species – we would simply put a tick mark against animal X and report it as ‘not extinct’ since that one last local population still exists. And here lies the problem.

This strict binary of ‘extinct or ‘not extinct’ is simply too coarse a method to capture the true health of an animal species in the wild. In this case, for example, by simply labelling animal X as ‘not extinct’ we fail to capture the critical detail that animal X is faring miserably because its local populations have suffered from a drastic decline: In this hypothetical scenario, from 15 to 1. Hence, the underestimation of the magnitude of mass extinction.

Therefore, according to the study in question, to better gauge the true estimate of the magnitude of the present mass extinction event, it is imperative that one should focus more on the extinctions of the local populations, and not just on the global extinction of a species. Just because an animal lives, does not imply it thrives.

All previous studies have followed the above, albeit flawed, approach: of concentrating only on the ‘end point’. And thus these studies suffer from the misconception that the phase of biodiversity loss is only just beginning, and humankind has the luxury of several decades to counter it. The rate of extinction, after all, is only two animals/per year. But the study in question asserts the contrary through rather aggressive rhetoric: “We emphasise that the sixth mass extinction is already here and the window for effective action is very short, probably two or three decades at most.” Probably, even less.

Of course, this is not to say that humankind will go extinct within a few decades; but that if we do not begin to act right now, then this mass extinction will prove to be irreversible after two or three decades. Consequently, the extinction of the human race will, in all likelihood, closely follow.

To back such a strong claim, this study follows a novel approach. It takes into account, unlike prior studies, two important factors that directly precede the ‘end point, i.e. the global extinction of an animal species. First, as delineated above, the decrease in the local populations of different animal species over the last hundred years. Second, the shrinkage of their geographical habitats over the same time. [Note: For this study, the local populations of 27,600 vertebrates were considered, which is a small fraction of the total number of animal species in the world, about 8.7 million7.]

The study reports that over the last hundred years about one billion local populations of different animal species have gone extinct. One. Billion. Again, to repeat, this does not imply that one billion animal species have gone globally/completely extinct in the world; but that a total of one billion local populations of different species have been wiped out forever in certain regions of the world while still probably being present in other regions of the world. Hence, ‘local’ extinction.

Thousands of local populations of the Asiatic Lion, for instance, were once found all over India. But over time, all these local populations – along with the one billion local populations of other animals – have gone extinct. Today, the last few local populations of the Asiatic Lion are now only found in an isolated pocket, the Gir Forest, situated in the state of Gujarat. Once these last few local populations go extinct, the Asiatic Lion will be declared ‘globally extinct’, not to be found anywhere in the globe.

The study discovers another disturbing fact.

Over the last hundred years, 32% of Earth’s vertebrate species have decreased in population size and range. Of the 177 mammals analysed in the study, all have lost 30% or more of their geographic ranges, and the ranges of more than 40% of the species have decreased by more than 80%. Even animal species – categorised as ‘Least Concern’ – too have been suffering from similar woes and are tending inexorably towards the ‘Endangered’ category.

Our data indicate that beyond species extinctions, Earth is experiencing a huge episode of [local] population declines and extirpations, which will have negative cascading consequences on ecosystem functioning and services vital to sustaining civilisation. Humanity will eventually pay a very high price for the decimation of the only assemblage of life that we know of in the universe.”

Therefore, even if only ‘two’ animal species are going globally extinct every year, this number – ‘two’ – belies the drastic and widespread extinction of hundreds of thousands of local populations of different animal species all around the world. Eventually, such local population and habitat losses will lead to the global extinctions of thousands of animal species over a short duration of time: mass extinction.

So, what do we do to counter this wave of local population extinctions, and thus in turn stall the sixth mass extinction?

To answer this question, one may talk of wildlife conservation programmes. Of ombudsman bodies. Of national policies. Of international partnerships. But the real answer to this question is one that we – and any high school student – have known too well and for far too long. An answer that has been repeated so many times that it seems to have lost its potency:

Reduce consumption3. Rein in population3.

Considering the unpalatable claims of the study, however, it should come as no surprise that certain scientists have taken issue with it and questioned its findings, and not without good reason.

These scientists find the study to be ‘alarmist’ and accuse it of crying Wolf! because mass extinction events are far more severe in their intent. These sceptics4 believe that since mass extinction events unfold over hundreds of thousands of years, it is simply too soon to convince ourselves we are knee-deep in another one. The study, after all, has considered the number of animal extinctions, and that too only of vertebrates, over only the last hundred years – a blink of an eye when compared to the duration of previous mass extinctions. What of insects and other non-vertebrates? By focussing only on 27,600 vertebrates, a small subset of the total 8.7 million animal species, the study may be reporting a mass extinction event that is far more severe, even exaggerated, in magnitude than what it actually is.

Furthermore, one may even argue, that the human animal may be able to engineer solutions to alleviate the ill effects of mass extinction. Again, as mentioned in the previous paragraph, it would be wise to note that a biological mass extinction event, after all, is not a sudden guillotine that would end all humankind with one swift fell swoop. Yes, thousands of animal species do go extinct at a high rate and over a ‘short window’ of time, but this short window of time stretches over hundreds of thousands of years. And this window of time could be time enough for the human to develop robots to pollinate trees. To artificially synthesise meat, if the world’s fisheries were affected. To even create disruptive technologies that could mimic the role of otherwise extinct plants and trees to ensure the atmospheric oxygen, along with other essential gases, is maintained at a certain vital level. By then, we may have even colonised other planets. So, the threat of mass extinction may not be as bad as it sounds, at least not to the human.

Yes, this study does claim that if we do not act now – two or three decades, at most – the mass extinction would be irreversible. Consequently, soon, the rate of local population extinction could rise cancerously from what it is now and result in a precipitous drop of biodiversity, thus threatening human survival.

But will the drop in biodiversity be quick and significant enough to outmanoeuvre human technological growth? This is one question that needs to be considered before we sound the alarm.

Yet, dare I say, since we have already wiped out 50% of our vertebrates over the last hundred years3, we could soon lose another 50% if something is not done. And, personally, given the momentum of extinction, I wonder if there will be time enough for the human animal to cope with it – through technology, or otherwise. Furthermore, such a rate of biodiversity loss could prove to be something that will be far greater than even the most catastrophic of the previous mass extinction episodes:

This makes it even more urgent. All previous mass extinction episodes spanned over hundreds of thousands of years, but this mass extinction is happening now, and over only a few hundred years!” Said Gerardo Ceballos, the lead author of the study, in an interview with me.

He continued: “And what of the sceptics you speak of? I know of only two scientists who say that there is no sixth mass extinction. If we do not act within the next two or three decades to reverse this mass extinction, our annihilation would be certain and complete. In fact, what is the point in waiting for the mass extinction to worsen in order to satisfy ourselves, beyond doubt, that it really, really is happening? Because then it would be too late for us to do anything. It is rather trivial to wait for the extinction to get over and say ‘Oh look it really did happen’, because by then we would have been long gone. We must act. Now.”


The tempest rages and gathers momentum, but the ostrich burrows her head deeper into her solace of ostensible peace. The ostrich also seems to forget that her wings cannot bear flight. Her limbs are fast, but only so fast.



1Ceballos, Gerardo, Paul R. Ehrlich, Anthony D. Barnosky, Andrés García, Robert M. Pringle, and Todd M. Palmer. “Accelerated modern human–induced species losses: Entering the sixth mass extinction.” Science advances 1, no. 5 (2015): e1400253.

2Wake, David B., and Vance T. Vredenburg. “Are we in the midst of the sixth mass extinction? A view from the world of amphibians.” Proceedings of the National Academy of Sciences 105, no. Supplement 1 (2008): 11466-11473.

3Ceballos, Gerardo, Paul R. Ehrlich, and Rodolfo Dirzo. “Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines.” Proceedings of the National Academy of Sciences 114.30 (2017): E6089-E6096.



6Kalinkat, Gregor, Sonja C. Jähnig, and Jonathan M. Jeschke. “Exceptional body size–extinction risk relations shed new light on the freshwater biodiversity crisis.” Proceedings of the National Academy of Sciences (2017): 201717087.

7Mora, Camilo, Derek P. Tittensor, Sina Adl, Alastair GB Simpson, and Boris Worm. “How many species are there on Earth and in the ocean?.” PLoS biology 9, no. 8 (2011): e1001127.

8Darroch, Simon AF, Erik A. Sperling, Thomas H. Boag, Rachel A. Racicot, Sara J. Mason, Alex S. Morgan, Sarah Tweedt et al. “Biotic replacement and mass extinction of the Ediacara biota.” In Proc. R. Soc. B, vol. 282, no. 1814, p. 20151003. The Royal Society, 2015.


Somendra Singh Kharola is a published poet and a freelance science writer based in Bengaluru. 

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Sorry, but why do you find this human-centred when the authors are going out of their way to mention that very large number of species are getting destroyed?

Krishnaswamy Sankaran

Because the focus is on how this extinction is going to affect the human species and the views of those who think that humans will find an S&T solution that will protect humans from the extinctions.


Well, the author suggests two points in terms of solutions. Reduce consumption. Rein in population. Neither are directly S&T solutions, although it is conceivable that S&T can play a role in both. So not sure about that objection. I mean sure there is a moral / ethical angle to it too, but given that those too are constructs of the human mind, I am inclined to think that the present problem is very much a human-related problem. Our species is the main culprit here. So I am not sure that I appreciate your anguish at this article being so human-centered in the ways that you state. Stated differently, which non-human-centric approach(es) you feel is being missed here?

Krishnaswamy Sankaran

Obviously the problem arises from the rapaciousness of a section of human consumption and lifestyles. This in turn arises from human thinking that the earth belongs to them only. My point was not nonhuman solutions. But the reasons for finding solutions is not altruism but self centred human survival. It is not the desire to save the planet and the diversity. But to find a solution because the human existence is threatened. Naturally any solution will stop once that goal is achieved. And by human existence is not all of humans but a section of humanity that makes the cake and ears it too.

Krishnaswamy Sankaran

Well written..topical...but the article and responses are very human centred..And therein lies our problem..Despite 300 years after Copernicus and 150 years after Darwin we still continue to think the Universe and the Earth are centred on humans. We cannot seem to think beyond our narrow selves.