Chris Doughty
Appearances
Short Wave
Love Fruit? Thank (Dinosaur) Mass Extinction
And so there was no evolutionary reason for seeds to get big. But what happened was after the dinosaurs went extinct, the forest got really dark.
Short Wave
Love Fruit? Thank (Dinosaur) Mass Extinction
For a little seed, that's trouble. You know, these little seeds, they need light.
Short Wave
Love Fruit? Thank (Dinosaur) Mass Extinction
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Short Wave
Love Fruit? Thank (Dinosaur) Mass Extinction
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Short Wave
Love Fruit? Thank (Dinosaur) Mass Extinction
That's right. So species go extinct all the time. And it's not unusual. It's just part of nature. But certain things happen that drastically accelerate this process, that make it so 80%, 90% of species go extinct. So what distinguishes a mass extinction from just a normal extinction is many more species are going extinct, and it's global.
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Love Fruit? Thank (Dinosaur) Mass Extinction
No, no, no. Yeah, it is difficult to try to piece these together. So the first starting point was we had colleagues that literally scraped off fossils from leaves right before the extinctions and pretty much right after the extinctions. And we could test the chemistry of those leaves, and we could actually say how much light these leaves got.
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Love Fruit? Thank (Dinosaur) Mass Extinction
And so for one of the first times, we were able to accurately quantify how much less light was in this understory after the dinosaurs went extinct. And then what we were able to do was go into rainforests and study how plants grow. And so, you know, from that perspective, we could see how tall would you get at a given seed size? And it's a very strong correlation.
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Love Fruit? Thank (Dinosaur) Mass Extinction
So if you're small, you develop into a tiny little seedling. And if you're a big seed, you develop into a big seedling. And then we can go even further and look at modern megafauna like forest elephants. and see, you know, how do they open up the understory?
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Love Fruit? Thank (Dinosaur) Mass Extinction
And so then what we do is we take, you know, all this information going from fossil records to how plants grow, to how seeds grow, to how forest elephants affect forests, and we put it into a model. You can think of it like a computer simulation.
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Love Fruit? Thank (Dinosaur) Mass Extinction
I don't know that one, but yes, like, you know, like, you know, SimCity or something.
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Love Fruit? Thank (Dinosaur) Mass Extinction
It would have been a very bright forest. It would have been very open. You have a lot of pine trees.
Short Wave
Love Fruit? Thank (Dinosaur) Mass Extinction
Exactly. Yeah. And then you just allow, you know, millions of years of ecology to happen. And so basically you just kind of input this into our model and then you see what happens.
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Love Fruit? Thank (Dinosaur) Mass Extinction
The verdict is, yeah, it worked. So, you know, basically what we saw was the darker understory basically created an evolutionary advantage for bigger seeds. And so those bigger seeds then created fruit that would entice bigger animals to eat them. And these bigger animals would distribute the fruits farther.
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Love Fruit? Thank (Dinosaur) Mass Extinction
And the trees that are moved farther away from their mother tree are very happy because you don't have to put up with the same diseases that your mother has. You don't have to be under her shade. And so that's an evolutionary incentive as well. So basically, they're bribing these animals with fruit to move them around.
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Love Fruit? Thank (Dinosaur) Mass Extinction
Yes. Our primate ancestors developed because they were good at climbing trees and eating fruit. And so had there not been fruit, you wouldn't have this incentive to climb up in the tree and eat fruit.
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Love Fruit? Thank (Dinosaur) Mass Extinction
Yes. At one point, all the seed sizes were getting bigger. And then about 35 million years ago, these seed sizes started getting smaller. And it was a big mystery as to, you know, what's driving this? You know, and what our model explained was that it was actually the evolution of these really large mammals now.
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Love Fruit? Thank (Dinosaur) Mass Extinction
The sauropods are the biggest terrestrial animal that's ever walked the Earth.
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Love Fruit? Thank (Dinosaur) Mass Extinction
You had all sorts of weird-looking mammal groups that grew enormous that are some of the relatives of what we see now out on the African savanna. They'd get really big, and then they'd start opening up these understories as well. Those big seeds were no longer way better than the small seeds. The seed size started to decrease.
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Love Fruit? Thank (Dinosaur) Mass Extinction
That's right. So that's another really interesting extinction event. Because it overlaps with us. So this is commonly referred to as the sixth extinction. There is a lot of tree species that co-evolved with these big animals to have them move their seeds around. So think of the avocado, think of chocolate, two of our favorite plant species.
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Love Fruit? Thank (Dinosaur) Mass Extinction
Those co-evolved with these now extinct South American elephants. So that's why you kind of see this increase in seed size over time more recently.
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Love Fruit? Thank (Dinosaur) Mass Extinction
That's right. Yeah. So, you know, I'm really interested in trying to predict the future with some of these models, not just thinking about the past. And so, you know, one of the fun things we did in this paper was say, all right, we went through another mass extinction recently of these really large, important animals. What do we predict for future seed size?
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Love Fruit? Thank (Dinosaur) Mass Extinction
And without these large mammals like the gomp, the fears, mammoths, giant ground sloths, these forest understories are a lot darker. And so our model would say, okay, well, it's dark. The seeds want to grow bigger again. But the interesting thing was we couldn't actually say that because there's another enormous ecosystem engineer that is dominant on the planet now, which is us. Oh.
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Love Fruit? Thank (Dinosaur) Mass Extinction
Exactly, yeah. So we've taken on the ecological roles of some of these now extinct animals. Oh, how so? Through logging and, you know, creating farms, creating grasslands. Like, you know, it's not uncommon for, you know, larger animals to create grazing lawns. We just call it agriculture. You know, they're excellent at distributing nutrients across the landscape.
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Love Fruit? Thank (Dinosaur) Mass Extinction
We're not so good at moving nutrients, but we dig up a lot of... You know, elements and, you know, spread it across the planet. And so a lot of these big animals used to consume a lot of this vegetation that, you know, when they went extinct, you got a big increase in fire. So, yeah, there's a lot of interesting ecological changes that occurred once these animals went extinct.
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Love Fruit? Thank (Dinosaur) Mass Extinction
And I actually have an interesting little tidbit for, you know, we are King Kong. And I don't mean that as a metaphor. I mean that we're metabolically King Kong. Wait, what do you mean by that? Humans, you know, use other energy. We heat our houses. You know, we have fires.
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Love Fruit? Thank (Dinosaur) Mass Extinction
They can knock down trees. They can distribute nutrients. They can move seeds. They do a lot of really important things. And big animals tend to do that differently than small animals.
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Love Fruit? Thank (Dinosaur) Mass Extinction
And so if you figure out how much energy we use, like by burning oil on top of like everything we eat, you could predict what size animal would be. Oh. And so we would be 8 billion King Kongs. We're metabolically 8 billion King Kongs running around the planet. And so, you know, we in the Western world consume a lot more energy than typical global citizen. We might be the Ultrasaurus.
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Love Fruit? Thank (Dinosaur) Mass Extinction
I haven't done that actual calculation. We might even be bigger than King Kong. So we're really changing this long-term evolutionary trajectory of the planet in interesting ways. But of course, who knows where we're going to be in a thousand years versus a million years. That's something that our models cannot predict, unfortunately.
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Love Fruit? Thank (Dinosaur) Mass Extinction
Yeah, I mean, I'd like people to reflect on our ecosystems co-evolved with these big animals. They're used to having these big animals both as nutrient distributors, you know, affecting forest structure. They play really critical roles and now they're missing.
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Love Fruit? Thank (Dinosaur) Mass Extinction
And so that's kind of like our motivating factor for creating these models is to, you know, say something about our future world on big spatial scales over long periods of time.
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Love Fruit? Thank (Dinosaur) Mass Extinction
That's true. That's not quite as fun to think about. But yeah, it's like the circle of life.
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Love Fruit? Thank (Dinosaur) Mass Extinction
Yeah, those same elements have cycled through your son that were in a sauropod someday.