Chris Thomas, Inheritors of the Earth book Ecologist Chris Thomas thinks we should focus on the world as it is instead of always trying to get back to a hazy past. (Photo courtesy of Chris Thomas)

Many scientists believe the Earth is about to enter its sixth mass extinction. Unlike previous extinctions, the blame for this one would fall on humans. As the thinking goes, this extinction would alter life on Earth in a way far more perilous than the changes wrought by the meteor that wiped out the dinosaurs 66 million years ago. The drumbeat of warnings about the consequences of this extinction often include terms such as "dire" and "catastrophic."

Chris D. Thomas marches to the beat of a different drum, though. In his book, "Inheritors of the Earth, How Nature Is Thriving in an Age of Extinction," Thomas makes the case that in the event of a sixth mass extinction, nature will do what nature always does, which is fight back. Furthermore, he contends, nature will win again — just as it has in previous extinctions. In fact, Thomas, a distinguished ecologist and a professor of conservation ecology at the University of York in the United Kingdom, believes that nature is already thriving, despite the gloomy outlook we often hear.

book cover of Inheritors of the EarthThe book is a passionate, thought-provoking and optimistic examination of the relationship between humanity and nature. Thomas makes the case that some aspects of biodiversity are increasing, not declining; and that human activity is natural, not unnatural, because humans, like every other form of life on the planet, came into existence through the production and consequence of physical, chemical and eventually biological processes. He urges readers to accept that the movement, gain or loss of plants and animals around the planet is the result of the human modification of ecosystems, and this is completely natural.

"We must accept that we are living in the so-called Anthropocene epoch," Thomas tells MNN from his home in York. (Anthropocene, which hasn't been formally adopted by the scientific community, refers to the span of time in which humans have been on the Earth and our impact on the planet. It comes from the derivatives "anthropo" for "man" and "cene" for "new." Technically, we live in the Holocene.) "The ecological and evolutionary processes of life are about gains as well as losses, and it is as equally legitimate for people to appreciate and promote new biological gains in the human epoch as it is for humans to regret the losses," he continues. "We must become accustomed to thinking that the world will continue to change, rather than hankering after some rose-tinted past that it is no longer possible to return to."

In this interview, Thomas talks about the reasoning behind the thoughts he expresses in the book, the genesis moment that led him to his conclusions and why he thinks people should accept the world for what it is rather than what they would like it to be.

MNN: You've been called a contrarian ecologist. Is this a fair assessment?

Chris Thomas: No. The point I am making in the book is that we should consider the gains in biological diversity at the same time as we consider the losses, and then contemplate our attitudes based on the balance of those. At the moment, the prevailing opinion is based on a rather one-sided view of the world in which change is often equated with loss. I'm not denying that losses are taking place. I am saying there are also ecological gains we should consider. Those gains are ecological in that the number of species are increasing in most regions of the world. That is a factual statement. It really can't be contested, although the number of species worldwide has declined. That's because more species are arriving in a particular region, whether that be a state in the United States, a country like the United Kingdom or an island or a set of islands like New Zealand. There are also evolutionary gains because new species have started coming into existence in the human epoch.

You write: 'It is time for the ecological, conservation and environmental movement to throw off the shackles of a pessimism-laden, loss-only view of the world.' What led you to our own genesis moment?

It has been a slow journey. I spent my career working on different animals and plants in different habitats in different parts of the world. I came to realize all of them had adjusted to the human-modified world in some way, and those adjustments were allowing species to live in places where they historically could not survive. Therefore, there were biological gains. Thinking of changes as equivalent to loss wasn't a completely balanced way of viewing the world.

You write that the extinction crisis is real and present evidence that the world is in the process of losing many species that existed before humans arrived on the scene. Yet, your basic premise is that nature is thriving. How do you explain this contradiction?

The contradiction is that elements of nature are increasing at the same time as other components of nature are declining. Nothing I could say would make the losses go away. A species becomes extinct, and that's it. However, as I said, more species are now living in most parts of the world. If I consider the United Kingdom, nearly 2,000 additional species of animals and plants have [been] established here. They range from the very familiar, like house sparrows, to rarer species like the box moth, which only feeds on box trees, mostly in people's gardens. Even poppies, which are thought to be traditional in the British countryside only exist there because humans altered the landscape. There were no poppies in Britain before humans. Everywhere you look, there are species that are doing very well in the human-modified world. That is what I mean by nature is thriving.

A male Italian sparrow in the brush The origins and taxonomy of the Italian sparrow are hotly debated topics among scientists. (Photo: L. B. Tettenborn/Wikimedia Commons)

When you talk about new species, are they new species or are they really hybrids of existing species, such as your example of the sparrow?

They are new species in that they meet the scientific definition of being a species. Remember that humans also hybridized in our past, and that hybridization is a normal part of the generation of biological diversity on our planet. Recent genetic research has revealed that nearly all species have experienced hybridization somewhere in their evolutionary past. Hybridization is not a weird thing. It is part of the way evolution works. Another way of saying this, perhaps, is to ask, "How distinctive are these new species?" The Italian sparrow is pretty much as distinctive as any other species in this group of sparrows.

Of course, some of the species that are going extinct are evolutionarily more distinctive than this. Take the great auk that died out in the North Atlantic. It used to breed on offshore islands from North America to the British coast. It was a flightless bird that hunted fish in the North Atlantic, and it didn't have any very close relatives. The razorbill was its closest relative. So this bird was unusual and, yes, this would be a high priority species to conserve — if it was still alive. However, if you look at the list of species that are listed as endangered by the International Union for the Conservation of Nature, you'll see there are very large number of species in there, many of which are closely related to other species on the list. We readily add these animals and plants to our endangered species lists, but many of them are no more distinctive than the new hybrids that are coming into existence.

You said humans have hybridized. What do you mean by that?

When modern humans emerged from Africa 50,000 to 100,000 years ago, they met up with existing populations of Neanderthals in Europe and Denisovans in Eastern Asia. Virtually all Europeans, for example, have a couple of Neanderthal genes in their genetic code, unless they have recent ancestors who came straight from Africa, maybe via the West Indies. In Eastern Asia, people also have the genes of Denisovans. The Native Americans who colonized from Asia into North America contained some of these genes. This is the normal thing. We are all hybrids. You've heard of hybrid vigor in plants. Well, an increase in hybridization in the Anthropocene epoch that we are now entering may not be a bad thing.

You seem to be writing from a 30,000-foot view. In the book, you say that the loss of species is happening worldwide, yet we may not notice it in the landscapes that surround us. At face value, this seems to be another contrarian view. Would you explain what you mean?

Worldwide, the number of species on the Earth is going down. But, in most regions of the world, though not in every region, the number of species has gone up. Let's say a plant species that lived only in New Zealand dies out, but the Monterrey Pine is introduced there from California, Acacia trees from Australia and willow trees from Europe. The outcome is that the number of species in the world has declined because the species that only lived in New Zealand has disappeared, but the total number of plant species in New Zealand is increasing. There is a paradox in that the number of species on Earth may be going down but the number of species in a region can still be increasing.

Tansy plants in bloom Battling the tansy plant in North America may be a losing battle. (Photo: Bogdan/Wikimedia Commons)

In the U.S., there's a strong native plant movement and a resistance to introducing non-native species into American gardens. Part of this belief is based on research that shows insects and other pollinators have an evolutionary relationship with native plants and do not recognize non-natives as food or as a breeding habitat. Another aspect is that non-natives crowd out native species. You get into this topic in writing about sparrows reducing bluebird populations. Yet you seem to suggest that because of humans, the globalization of the planet's species is inevitable. What would you say about this to the concerns of the native plant movement?

That's a very well-put question, but the answer is very complicated. The first thing I would say is that, of the several thousand non-native plants species that are already in North America, you must ask: Is it possible to remove them? Is the amount of money being spent on controlling them worthwhile?

For example, when I visited Missoula, Montana, I went into a local park and there were some guys spraying tansy plants with an all-purpose herbicide. Now, tansy is a European plant. The problem is that it has small seeds and it regenerates on bare ground, which they were creating by spraying! So, what they were doing wouldn't work very well. And it's expensive. Even if they managed to spray it out of the park, in the long run, it wouldn't work because the plant is far too widespread in the landscape to be able to spray it all. If you think on the timeline of centuries, the plant is still going to survive in North America, so why spend so much money and effort fighting a war that you will inevitably lose?

The second issue is that introduced species can have beneficial effects on native species, and then it becomes more complicated to decide what to do. For example, the rare North American southwestern willow flycatcher nests in introduced tamarisk. In the modern human-transformed world that we now live in, it's no longer possible to unpick which parts of the environment can be thought of as pre-human and which parts have been altered by humanity. Everywhere in North America has been altered by humans, ever since the Native Americans arrived and eliminated most of the large mammals — the mammoths and mastodons and so on. North America's vegetation, the whole of it, in fact the whole of the world's vegetation, would be different today if these large animals were still around.

The idea that we are somehow keeping the world in a pristine natural state is a kind of mirage because the entire planet has already been transformed by humans. And climate change means that even the places that we think of as quite natural have changed in the last 50 to 100 years. The reality is that the world is dynamic and the distributions of species are changing. You can try to intervene and keep things as they are, but this is not how the biological world works. With climate change set in motion, it will be impossible to keep things just as they are. What I'm saying is, go with the flow a bit more and choose carefully which fights you are going to fight because otherwise you are going to throw good money at losing battles.

A tree branch and a human grasp Humans have had a significant impact on the planet, and we should come to terms with the fact that we will continue to change nature. (Photo: Nikolay Litov/Shutterstock)

If humans are altering the dispersal and survival of species, as you seem to be saying, are we altering the very forces of nature itself? Could you share your thoughts on this?

I take it as a given that humans have evolved and everything we do is directly or indirectly a product of human evolution. Therefore, it's hard to talk about nature as being a separate thing from us. We are part of nature, and in that sense we are part of the force of nature, rather than altering it in some fundamental way. But we still have major impacts, that is certainly true. We have become an extremely numerous large mammal, living throughout the world, changing the vegetation, killing animals to eat, clearing the land for our domesticated animals and cultivating the soil for our crops.

We have had an enormous impact on the planet. Don't get me wrong. And it is because of that enormous impact, I am arguing, that it is impossible to go back to the world as it was before humans arrived. We have changed it. We will continue to change it for the coming several centuries, so long as there are large numbers of humans on the planet.

Are we creating an 'unnatural' natural world that is perhaps like a giant laboratory or that is similar in at least some respects to the way GMOs are changing the agricultural landscape?

The world is a bit like an enormous experiment. The world has never seen anything like humans before: highly intelligent, group-living, hunting and farming primates. As a result of humans existing, the world has changed a great deal. However, most of the ways we are changing the world are not completely unprecedented. There is radiation in the world. Animals such as beavers build houses to live in. Other animals are farmers. For example, leaf-cutter ants tend and eat fungi, which they grow in underground nests. Most of the things we are doing are kind of comparable to normal ecological processes.

Perhaps the greatest change is the rate at which we are moving other animals and plants around the world. Species have very occasionally made it from one continent to another in the past, but this trickle has grown to a torrent in recent times, to such an extent that the current rate of movement is the greatest it has been for at least the half-billion years. It's like we have reunited all the continents into a new version of Pangea. It's like we are connecting up the world. This is an unprecedented experiment. But the outcome is that the most successful animals, plants, fungi and microbes will tend to rise to the top. And with more robust species, on average, you can expect future ecological systems to end up being more robust as well.

You write that when the asteroid hit the Earth 66 million years ago and led to the extinction of 75 percent of the Earth's species that the inheritors of the Earth had already been here for millions of years. Likewise, you write that the future inheritors of the Earth also have been with us for millions of years. The fauna and flora that survived the asteroid adapted to a new but 'natural' pre-human world. The next inheritors will adapt to a post-human world. Perhaps this is an esoteric theological question, but are humans natural? In any case, could you summarize the different challenges the future inheritors of the Earth will face versus those faced by the asteroid inheritors because of the presence of humans?

I see no rational explanation for the existence of humans or other life forms on this planet other than the production and consequence of physical, chemical and then eventually biological processes. Therefore, I regard humans as part of the natural system rather than separate. We are unusual, but I regard us as being a part of the same global system.

I understand, of course, that some people will take this differently. But I would still say that, even if you think we are completely separate from the rest of nature, the reality is that the whole of the rest of nature has been so strongly influenced by human activities during the last 10,000 years, and more, that it is too late to go back. When we talk about change today, we are talking about changes to an already changed system. It isn't possible to separate humans and nature any longer. So even if you think, philosophically, that there is a separation, in practice you can't really draw a line between the impacts of humanity and the impacts of other processes.

An illustration of a post-human environment, with plants taking over buildings Are flora and fauna prepared to adapt to a post-human world? (Photo: denisgo/Shutterstock)

You write that nature is fighting back and that nature loves a winner. If we could come back in a million years, or 10 or 20 million years, what plants and animals that we see today would we see then? Who will be the winners?

I concentrate in the book on the processes that have been taking place in the recent past. We might be able to imagine what can happen in the very near future. But the moment we start talking about the long-distance future, which I do discuss a bit, then we must think about how long humans will survive, what technologies we will develop and so on. It's sort of an impossible question to answer. Going back to the last question, the species that will be living a million years from now will all be descendants of today's species — unless we manage to create artificial life. We are not going to get a new set of species. Some of them might evolve to be a bit different than they are today, but they won't be hugely different after one million years. In terms of evolution, that's quite a short period.

So there will be familiar species and types of species, but often living in different combinations and different places than those we currently associate them with. If you look back at the last 10,000 years and at the last million years of intermittent ice ages and warm periods, species have always moved around. That's how they survive when the environment changes. Whatever the conditions will be 1 million years from now, we can expect that there will be new combinations of species in new places and they will have adjusted to the new conditions that will exist at that time. We will see familiar types of creatures, but we might be surprised by where they are living.

What would you like the casual, non-scientific reader of your book to learn from it?

Every time you think about some loss that is taking place, and you want to do something about it, that's great. But also ask yourself these questions: If I take action to stop this loss, will it make any difference in the long run, and can I also identify biological gains that are taking place? The ecological and evolutionary processes of life are about gains as well as losses, and it is as equally legitimate for people to appreciate and promote new biological gains in the human epoch as it is for humans to regret the losses.

Any final thoughts?

We live in a biological world where everything is dynamic: New species turn up and thrive in new places all of the time. Appreciate the world for what it is, rather than spending time being sad that the world isn't how you think it was supposed to be some centuries ago.