Thought Leaders

Are We Heading Towards a Sixth Mass Extinction?

Thought LeadersRobert CowieResearch ProfessorPacific Biosciences Research Center, University of Hawaii

AZoCleantech speaks to Robert Cowie from the Pacific Biosciences Research Center at the University of Hawaii about his team's research on the Sixth Mass Extinction. 

How did you begin your research into mass extinctions?

As a child, I was aware of the drastic declines of many well-known species of African wildlife, so I was aware of the need for the conservation of biodiversity from an early age. But it was not until I came to Hawaii in 1990 that I was faced with extinction on a massive scale – of native Hawaiian biodiversity, with the vast majority of species unique to Hawaii.

Although I published on conservation and extinction (of Pacific island snails) early on, I only became heavily involved in research specifically on the Sixth Mass Extinction, once I  began collaborating with my colleagues in the Muséum national d’Histoire naturelle in Paris a little over a decade ago, initially as a member of a graduate student’s PhD committee. We published two papers in 2015, a third in 2017, a couple of book chapters, and now the paper that prompted this interview.

What are the five confirmed mass extinctions we know about?

End of the Ordovician period (450 Million years ago [Mya], 85% extinct), end of the Devonian (365 Mya, 75% extinct), end of the Permian (250 Mya, 96% marine, 70% terrestrial extinct), end of the Triassic (200 Mya, 80% extinct), and end of the Cretaceous (66 Mya, 75% extinct).

What is the IUCN Red List and why is it heavily biased?

The Red List is a list of all species for which the International Union for Conservation of Nature (IUCN) has evaluated a threat status – from Critically Endangered, Endangered, Vulnerable (the “Threatened” categories), to Near Threatened, Least Concern, and Data Deficient (species for which there is insufficient data for their status to be evaluated).

As a byproduct of this process, species that are evaluated but found to be extinct, are also listed. However, the Red List has only evaluated a tiny fraction of all known species. It has evaluated all known birds and almost all mammals, but these are not a random sample of overall biodiversity.

Larger species tend to have larger ranges and are therefore less likely to be vulnerable to local habitat destruction than smaller species (most invertebrates).

Many rare invertebrates inhabit remote tropical regions, which is why they are so little studied and poorly understood. Given their likely small ranges, they may well be very prone to extinction, yet there is insufficient knowledge to evaluate them. Therefore, Red List evaluations are heavily biased to better-known species. They may also be biased towards threatened species, groups benefitting from being the target of IUCN “Specialist Groups”, or in some cases regions with higher species richness.

Can you tell us about the Sixth Mass Extinction and the key findings within your team’s study?

All species go extinct eventually – so there is what we call a background rate of natural extinction. This has been interrupted by five previous events of greatly increased extinction rates over relatively short periods of time – which we refer to as mass extinctions – all resulting from natural phenomena.

What we are now seeing is another period of a much-increased rate of extinction, perhaps 100 times the background rate, this time caused entirely by humans. If this continues, and there is no reason to think that it will not, then we are at the start of the Sixth Mass Extinction.

There are approximately 2 million species known to us – though there are estimated to be many more that we have yet to discover, so probably around 10 million in total. We estimate that in the last 500 years, between 7 and 13 percent of those 2 million species that we know have gone extinct – that is, between 150,000 and 260,000 species, so perhaps roughly 10% of known species, and therefore a much higher number of all (known and unknown) species.

Why have island species suffered far greater extinction rates than continental ones?

Oceanic islands are isolated by the surrounding ocean. Once a plant or animal has by accident reached such an island – which is a very rare event – it is free to evolve in the absence of many of the threats it would have faced in its original habitat. It becomes a new, different species, or even radiates into a number of different species – and all these are only found on this one island.

If humans destroy the habitat where they live, for instance by deforestation – or if humans introduce an invasive species that prey on them – the range of these species is so small that they are easily and completely extinguished, and go extinct. Species in continental habitats, in contrast, may have larger ranges and are therefore less susceptible to such impacts.

Is it fair to say that humans have caused the Sixth Mass Extinction?

Yes, humans are causing what may well turn out to be the Sixth Mass Extinction. The primary driver of this process is habitat destruction. This is intertwined with the impacts of invasive species. Of course, for certain species, killing them for monetary profit (think rhinos) is driving them to extinction.

Climate change is probably going to drive some species to extinction in due course; for instance, species adapted to the tops of high mountains, where it is cold, will have nowhere to go as the climate warms.

Is there a potential way that humans could help reverse this extinction?

We cannot bring back species that are extinct – they are gone forever – so there is no reversing what has already happened. Ideally, however, we should attempt to stop further extinctions, and if that is not possible right now, to at least slow the rate of extinctions. I do not believe that there is a political or economic will to do either, except for a few charismatic species, and even then we are failing – think about rhinos and gorillas, for example.

Can you explain what conservation biases are, and how this affects your hypothesis?

I’m not sure we have or had a ‘hypothesis’ regarding the Sixth Mass Extinction – rather, we looked at available data and extrapolated from those data to estimate the number of species that have gone extinct since around the year 1500, trying to avoid the biases I mentioned under question 3.

Is there evidence that suggests that the Sixth Mass Extinction is evolutional? What evidence is there to oppose this scientific viewpoint?

It is an opinion, held by some people, who argue that as humans are just animals going about their business in an evolutionary context, and that although we are demonstrably the cause of the current increased rate of extinction, this is simply an evolutionary phenomenon – humans will do what we do and we should just not worry about increased rates of extinction caused by us because that is a natural evolutionary phenomenon, so just go with the flow. In contrast, my opinion is that humans are not just another species but are the only species that has the capability of causing such dramatic impacts on Earth’s biodiversity, but that we also are the only species that has the conscious choice to continue to let it happen or try to stop or slow it. Since we have this choice, my opinion is that we should try to stop the destruction. This is not science, it is a moral choice.

What practices must we adopt to protect our ecosystems further?

Conservationists have suggested several approaches to help establish priorities for action, including, among many others:

  • Focusing on areas with both the highest diversity and threat level, i.e. biodiversity hotspots
  • Selecting species on which to focus based on the threat level and evolutionary uniqueness
  • Taking into account taxonomic, evolutionary, and functional diversity
  • Integrating ecosystem services in conservation planning
  • Taking into account human population pressure, habitat and protection status
  • Capacity building in megadiverse countries
  • Increasing efforts to combat extinction denial and passive extinction acceptance
  • Improving public education and outreach to address science denial in general

I doubt much of this will have much widespread and long-term success in staving off increasing extinctions. This is why we advocate a major effort to collect representative specimens of as many species as possible, especially those as yet undescribed and scientifically unnamed invertebrate species before they vanish and are lost and gone forever. In this way, in 200, 300, 500, or whatever years, our descendants would still be able to know and marvel at the biodiversity that the Earth once supported and that humans have destroyed.

Can you explain what preventive archaeology is?

The purpose of preventive archaeology is to discover and undertake the scientific study and preservation of archaeological remains that might otherwise be destroyed by land development, thereby safeguarding the archaeological heritage of a site. We are advocating something analogous in terms of preserving our biodiversity heritage in the face of its ongoing destruction.

Where can readers find more information?

The paper that prompted this discussion:

The IUCN Red List of Threatened Species:

The Sixth Extinction: an Unnatural History:

Evolution, Extinction and Conservation of Native Pacific Island Land Snails:

About Robert Cowie

  • I have a BA and MA from the University of Cambridge and a PhD from the University of Liverpool, all in Zoology. I worked as a postdoctoral researcher for three years at University College London. My PhD and postdoctoral work was on the ecology and genetics of snails, notably of one species that has become a major crop pest when introduced to various parts of the world.
  • I then spent four years as head of a small British Government research group working on the ecology and control of termite pests of crops and forestry, primarily in Africa.
  • I moved to Hawaii in 1990 where I took charge of the mollusk collections of the Bishop Museum in Honolulu. This is the premier natural history museum for the islands of the Pacific. This is where I began getting interested in extinction, as the incredible and unique diversity of the land snails of the Hawaiian and other Pacific islands has suffered extremely high levels of extinction. I also became interested in invasive snails that have become agricultural pests and human disease vectors, and others that have been instrumental in the extinction of the native snail species.
  • After over ten years at the Museum, I moved to the University of Hawaii as a researcher, continuing my work on non-marine snail biodiversity. In 2005, I began collaborating with researchers at the Muséum national d’Histoire naturelle in Paris, and part of this collaboration was on the extinction of land snails and of invertebrates and biodiversity more generally, which led to a number of publications, including the one that is the focus of this interview.
  • The other main current focus of my research is a very different topic – rat lungworm disease. This parasitic disease can be fatal in humans, who contract it via ingestion (raw) of the snails that, along with rats, act as key hosts of different stages of the life cycle of the parasite.

Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of Limited (T/A) AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms and Conditions of use of this website.

Laura Thomson

Written by

Laura Thomson

Laura Thomson graduated from Manchester Metropolitan University with an English and Sociology degree. During her studies, Laura worked as a Proofreader and went on to do this full-time until moving on to work as a Website Editor for a leading analytics and media company. In her spare time, Laura enjoys reading a range of books and writing historical fiction. She also loves to see new places in the world and spends many weekends walking with her Cocker Spaniel Millie.


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