RENEE MONTAGNE, HOST:
Here's a story about something that won't make the news, should it ever happen - a future world in which humans go extinct and another species takes over the earth. Science reporter Flora Lichtman envisions what that would be like as host of a podcast on climate change called The Adaptors.
FLORA LICHTMAN, BYLINE: Paleobiologist Jan Zalasiewicz has this thought experiment. It's dark. Humans go extinct and the question is, what comes next? Jan's point is less about our impending doom and more about providing prospective on how we're transforming the earth in this unprecedented way, and how that could be threatening, even to us.
JAN ZALASIEWICZ: We're changing climate. We're changing the chemistry of the earth. We're changing biology of the earth. We're also quite aggressive amongst ourselves. So, you know, as people have speculated, there are all kinds of dangers ahead, you know, what have been called existential threats for humanity. So I think for many reasons it's good to stand back and say, OK, let us see what the world would do like without us.
LICHTMAN: Jan writes about this in a book called "The Earth After Us." And in it, he tosses out this idea that the animals best suited to take over after we're gone are rats.
ZALASIEWICZ: Some will become big, some will become small, some will become fat, some will become thin, then taking over to fill those niches that we have vacated and the elephants have vacated and the rhinoceri have vacated.
LICHTMAN: So we can visualize, actually, like, an elephant-sized rat grazing somewhere on the savannah?
ZALASIEWICZ: Yes, of course. The whale rat, the seal rat, the walrus rat would be a very nice one. They're already pretty smart, so some might become really quite smart. And, you know, we may have the rat civilization.
KATHERINE WELLS, BYLINE: So I love this as a thought experiment...
LICHTMAN: This is producer Katherine Wells.
WELLS: But I do have a question. How real is this?
ZALASIEWICZ: Well, one real thing is whether we will survive or not, you know, for any significant geological length of time. And that is really completely up for grabs.
WELLS: OK, so when I first heard about this research, I was kind of blown away. First of all, the idea that we might actually go extinct - I had never heard this before. But second of all, the creature best positioned to take our place is a rat. If this is even remotely a real possibility, why are we not all talking about it all day long?
LICHTMAN: Right, and then it's like what makes rats better positioned than us?
KEN APLIN: I like rats. I really like them.
LICHTMAN: This is biologist Ken Aplin. He's researched rats at the Smithsonian and museums in Australia. And he says that rats are super-adapters.
APLIN: Rats and mice have hit on a really great - they have this combination of relatively fast lives, short reproductive periods, and high potential to increase their populations in response to resources becoming available in the environment. They're ideally positioned to take over the world.
LICHTMAN: This is an advantage that rats have over, say, non-human primates, which have longer generation times and so can't increase their populations as quickly. Others have suggested that cockroaches, crows, snakes might also be good candidates for world domination. But rats have other useful traits.
ZALASIEWICZ: They're quite adventurous in what they eat. So I guess there's a lesson for us there. You know, we tend to be fussy.
LICHTMAN: We might take a cue from rats, here. The U.N., in fact, has suggested that we might eat more insects as a climate change mitigation strategy.
ZALASIEWICZ: They can live in hot climates and pretty cold climates without, you know, anything but their own fur coats.
LICHTMAN: After rats, or whatever creature takes over the earth, they would likely evolve and change. Biologist Ken Aplin imagines how a social animal like this might build a civilization.
APLIN: If rats, for example, were to start to try and farm resources the way people have farmed resources, it would need to be something on a different timescale.
LICHTMAN: Because their livestock would outlive them.
APLIN: Maybe resources like algae and seaweeds, maybe some kinds of insects.
LICHTMAN: They could farm cockroaches or something.
APLIN: Termites, why not? They've got great dexterity. Do they have the intellectual capacity to do it? It's hard to say because they're a bit impenetrable to us. It's very hard to know what's really going on in a rat's mind.
LICHTMAN: From what we do know about the rat psyche, though, a future Ratocene may face similar problems to the problems that we face.
APLIN: In situations where food starts to get a bit tight or where there are just too many individuals, then the system can start to break down a little bit. And instead of aggression, just being a deterrent, it can progress to murder most foul. We see many parallels in those brown rat colonies when they're placed under environmental stress, so a lot of the same kind of dysfunction that we might see in human society.
LICHTMAN: That's depressing. You know, if this is what happens to a species under stress, does this seem like a creepy foreshadowing of what's to come for us?
APLIN: (Laughter) Gloomy thoughts, yeah.
LICHTMAN: The fact that this future rat society is oddly reminiscent of our own, that's part of Jan's point.
ZALASIEWICZ: Zooming forward to the far future, and maybe it'll even be one species of hyper-intelligent rat asking this question, they'll look back at humans. One take-home message that they will immediately say is that humans did all this and wiped themselves out extremely quickly. I mean, geologically, you know, we've been around for much less than a million years. Humans that have made complicated industrial things, you know, using coal and oil and gas - they've only been around for about 200, 300 years. And let us say, we blow ourselves up very quickly. We will look like some very rapid, highly interesting but highly unstable creature. So they may think that it's better to have a society dominated by many kinds of slightly less damaging rats. You know, maybe they will learn to live - what's the word - more sustainably than humans have managed to do yet.
LICHTMAN: They can learn from our mistakes.
ZALASIEWICZ: Yes, that's right. They can learn from our mistakes, yes.
LICHTMAN: For NPR News, I'm Flora Lichtman.
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