Could we be good for nature? An interview with biologist Chris D Thomas

Chris D Thomas believes we are selling ourselves short

Though extinction rates are ‘exceptionally high’, the biologist also thinks the human race is not a categorical loss for life on Earth. ‘Huge numbers of species are thriving in the human-altered world,’ he writes in his book, Inheritors of the Earth: How Nature is Thriving in an Age of Extinction, ‘and we may even be stimulating a mass diversification of new species.’

How are species becoming more diverse with human help?

‘Hybridisation is a good example. This is where you get a new species forming from two different parent species. Hybridisation is a key driver of the creation of new species – otherwise known as speciation.’

Do you have any good examples?

‘A new species of monkey flower is now growing by Scottish streams. Without human activity it could not have come into being as its two parent species are from South America and North America. Nonetheless, they would have been brought into British gardens, spread into the wild and created a new species. In Britain alone, hybridisation has created seven or eight new plant species that have come into existence through such hybridisation since 1700.’

...and that’s fast?

‘In fact it’s about a hundred times faster than average across the geological past.’

Are humans speeding it up?

‘With global travel as ubiquitous as it is, species are reaching each other that never could before. It is entirely credible that the current rate of speciation is the highest ever in history. We don’t know that for certain, but the fact that it could be changes the relationship between humans and nature, don’t you think?’

How do you want us to see invasive species, or new hybrids caused by human activity?

‘Species like the new monkey flower present a real dilemma for conservationists. Should they kill the new alien plant or celebrate it?’

Which side do you lean towards?

‘What I call for is a philosophical change as much as a scientific one. I argue that the species gains should not be downgraded as a loss just because they were caused by human interferences such as settlements, climate change or globalisation. There is nothing less “natural” about the species that are benefitting from our presence. And really, if we want to succeed in conservation aims, we should be hanging on to as many species as possible.’

How does that make you feel about humans?

‘We cannot simply undersell ourselves as the terminators of species. We are also very effective dispersal agents. Both things can be true.’

You demonstrated your point in an unusual way...

‘When I was a child I thought I could dig to Australia, but as a 50-something academic I thought it would be more interesting to try to visit the Ice Ages. I live in the Vale of York, which has seen some pretty fundamental ecosystem changes in the last 20,000 years.’

What did you find?

‘I’ll start from the bottom up. At a metre and a half there is a gloopy clay. It is the remains of a lake bed which would have been at the edge of a glacier 15,000 to 20,000 years ago. The glacier would have sat over the North York moors and the Pennines and caused an ice dam.’

15,000 – 20,000 years ago

‘This lake would have been filled with Arctic char and surrounded by species we associate with the north. Arctic foxes and snowy owls for example.’

‘Above the clay is about a metre of sand. It is the remains of a sand dune from around 12,000 years ago. It would have been created when the water was drained from the lake and dry sediment blown into hills.’

11,500 – 12,800 years ago

‘This new ecosystem would have had mammoths and woolly rhinoceroses grazing on its steppe-like vegetation. That amazes me. If I was standing there back then, it would have been possible to see herds of these mega-beasts wandering past. Yet in the history of life on Earth, 12,000 years is like the blink of an eye.’

‘Above that we get a richer soil, as the Holocene brought about warmer climates and forests moved in. Moving into the bronze age, the forests would have been cleared for agriculture. Now it is a hay-meadow.’

10,000 years ago

And the ecosystems would have been different after each of those transitions?

‘Completely. There would have been a total replacement of all of the species. A biologist would have found the lake to be a fantastic ecosystem. The dune system would have had some of the largest mammals on the planet. Then it became a forest, then agricultural. These days it’s effectively a grassland and it’s a different set of species yet again. With each of these transitions, the ecosystems would have been entirely populated by incomers. New species arriving.’

So, are the world’s ecosystems in a similar transition today?

‘Today the biological world has been changing very rapidly. As we enter the Anthropocene, species are changing faster than ever – and they are changing where they are thriving. Some are migrating or disappearing and others are beginning to turn up. Often, we’re looking at this thinking: we don’t like the old ones going, and we don’t like the new ones arriving.’

Do you think we are interpreting it as a lose-lose situation?

‘Often, yes, and it doesn’t have to be. The ecosystems of the planet have always operated by the arrival and departure of species. Departure when the environment is no longer suitable for something, arrivals as opportunities appear. That’s how things will survive. Trying to micromanage the world back to some imagined past is actually working against the responsiveness of nature and the capacity of ecosystems to adjust.’

How do you feel about non-native and invasive species?

‘So far, there are roughly 2,000 non-native plant and animal species that have made Britain their home. They are often portrayed in a negative light, even when new species arrive they diversify. When rodents arrived in South America, a few million years ago, they evolved into hundreds of different species. If we exterminate the successful “non-natives” we might just be killing off the descendent species of the future.’

Does that mean we should do more to celebrate the gains?

‘We should also try to enable them. It is just as legitimate for us to ask how can we maximise gains as well as how we can reduce losses. I am arguing for an “as well as” approach.’

How does this change how you think about the sixth mass extinction (a loss of 75 per cent of animal species)?

‘First of all, I think we’re going to avoid the sixth mass extinction. A lot of species are threatened, but with our actual observed rate of extinction it’s going to take the best part of 10,000 years to get there. Now here’s a scary thought: if we consider that humans began exterminating the largest mammals 60,000 years ago and may continue to for the next 10,000 years (70,000 in total), that would actually make this one of the fastest mass extinctions. The one that killed the dinosaurs was an exception in that it was relatively instantaneous.’

‘Fortunately, 10,000 years gives us long enough to do something about it. You can interpret most of the discussion about the sixth mass extinction as a way to prevent it from happening.’

So there is hope?

‘The way I see it, the biological system is always continuing, and there are very large numbers of species of an enormous diversity of taxonomic groups that are going to make it – so long as we don’t unleash some completely new forces that we haven’t imagined yet, and so long as we let opportunist species thrive.’

Given that we can’t predict, what do you think effective conservation ideas are?

‘I’m not saying that we should give up doing what we are currently doing. For example, we have seen in Britain that species as they change their geographical distributions in response to climate change are disproportionately colonising protected areas that weren’t established for them. What does that mean? It means we need to protect places where species already are, places where they are going to end up and the places in-between. We need more protection, not less. It would reflect that biology is always a work in progress.’

So it’s like shooting a moving target?

‘What we sometimes do today is say well, change is bad therefore let’s stop change. Which is no longer a realistic solution. There are growing human pressures, growing populations and warming temperatures. Of course, we should continue to reduce future change, however, “no change” has been off the table for centuries.’

‘Really, it is the direction and rate of future change that we need to be paying attention to.’

By Laura Cole

Chris D Thomas spoke to Geographical at the Brain Bar festival in Budapest

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