Phoenix last year went nearly four straight months without seeing high temperatures dip into the double digits; things weren’t that much more comfortable in the fall, either. So, we’re asking some questions about this, like how do we adapt to live more comfortably as these elongated summers become the reality? And, how can we better address extreme heat to provide communities with more shade?
There are a number of ways to provide shade — from planting trees to planning buildings and other structures. And, we’re talking about this as part of The Show's ongoing Throwing Shade series.
Today, we’re heading to a small island off the coast of Puerto Rico, known as Monkey Island, which is home to nearly 2,000 Rhesus macaques. In 2017, Hurricane Maria devastated the island’s vegetation, destroying more than half of it. And that’s where Camille Testard, a researcher at Harvard, comes in.
Testard studies the evolutionary drivers of social behavior, including how the macaques adapted to much less shade after the hurricane. Testard joined The Show to discuss.
Full conversation
MARK BRODIE: It sounds like one of the things you found is that this species of monkey, which is generally fairly aggressive and not the most friendly, once a good amount of their shade cover was destroyed by the hurricane, they became more willing to cooperate, especially as it related to shade, is that right?
CAMILLE TESTARD: Yeah, that's correct. So, the species of monkeys, Rhesus macaques, is really known to be the most aggressive, or amongst the most aggressive of primate species. They're super hierarchical. So typically, they don't really share things, and in the aftermath of the hurricane, the observers, so we have two research assistants that have been studying this population for over a decade, and I'm one of the people who uses the data that these guys collect.
And, when I chatted with him, with them at the beginning of my PhD, that's the first thing they told me, they were like, “Oh, it's really strange. These monkeys are, they're less aggressive, they hang out with more monkeys than they used to. They form these large clicks that they didn't used to form, and they do so sort of kind of across the day, and we don't really know what's happening.”
And that's kind of what was the impetus for my study, and it seemed that essentially that's what we found, that they, there was a destruction of the vegetation. Over, close to 70% of the vegetation was destroyed overnight, and then in the years that followed the hurricane, that vegetation is not recovering, so it actually became worse. So, we're actually seeing a desertification of the island.
And originally, you know, one thought was that maybe actually because there's less resources, there's more competition, we're going to see more aggression. And then when I talked to Jose and Danny and they told me “no, no, it's actually the opposite,” that was sort of very surprising to us, and it seems that they, instead of being more aggressive, are sharing more of their resources. They are much more tolerant with each other. They're interacting with monkeys they did not used to interact with, and overall are less aggressive.
BRODIE: How much of that do you attribute to the fact that they are in a place that is sunny and and gets pretty warm, and there is far less shade now than there used to be?
TESTARD: Yeah, so, that's a great question. I think that when we think about how our environment affects our social interactions, we tend to think first of resources and competition for resources. And if you think of food, well, if there's less food and, you know, if I eat, then you won't be able to eat, that’s a type of resource that really, maybe requires, aggression when there's a lack of, when there's not enough, for example. Versus, shade is a little different. Shade can be shared up to a certain point where if I sit in the shade, if you come in as well, that's not going to reduce my access to shade up to a certain point.
But the other reason is that the main pressure after the hurricane, let's say the main issue these monkeys are facing is heat. It's just really, really hot, and if you are battling with issues of heat and heat stress, and you are at risk of a heat stroke, being aggressive and chasing around other monkeys is actually not the best strategy. The results of that is actually increasing your body temperature.
BRODIE: Well, it's interesting because on the one hand, you have this idea of sort of self-preservation, right, as you say, you know, chasing around somebody else aggressively when it's really hot and there isn't a lot of shade and maybe fewer food and drink resources is not a great idea. But on the other hand, it's almost like a form of altruism maybe where the monkeys recognize that “just because I have shade doesn't mean somebody else can't. Like I can share and we can both benefit.” It's interesting you have these kind of competing ideas going here.
TESTARD: Yeah, that's right. And I think it's very difficult to say for sure whether the monkeys are engaging in altruistic behavior, or if it actually is the result of aggression being now so costly.
BRODIE: Well, it seems like regardless of what the rationale is on the part of the monkeys, they're still realizing that, you know, shade is important and are for whatever reason, willing to share it and be a little more friendly about it.
TESTARD: That's right, exactly, yeah.
BRODIE: So, does this tell us anything about humans? Like, can we extrapolate anything about this out to how humans behave, especially as it relates to shade and heat?
TESTARD: Yeah, I think, as it relates to shade and heat, well, that's a good question. And I think in general the answer to that question when you study primates is, is yes, you know, we're close evolution, we're very close in, in evolutionary terms, so they are sort of our cousins. So, a lot of how they interact with the world is similar to how we interact in the world. And I, I think that there's definitely some parallels with, well, I typically think of this first in terms of, it was a hurricane, that was a big traumatic event, and in response to big traumatic events, we actually find that humans tend to be more prosocial and help each other more, more altruistic, as you, as you were saying. And in a sense, that's also what we're seeing in the macaques.
And in the long term, I think that it's very interesting to see how an ecological factor that is really heat and access to shade, this very sort of environmental factor, is profoundly shaping how these individuals are interacting with one another. The extent to which they interact, who they interact with, and I think it's very interesting to think about how this might also be true in humans. When now if there's only a narrow space of shade where I feel comfortable and my body temperature is comfortable, but it also happens to be next to these strangers, where I'm also more likely to interact with these strangers and maybe build new friendships with individuals, I would not have normally built those, those friendships, but I just kind of happen to be in that same space.
But also what we see in the monkeys is that we, we see that the monkeys that form relationships under the shade are also interacting more outside of the state. So, say early in the morning, or in the evening when it's not as hot, now we also see them interacting with each other. And so, there's sort of, I think a spillover effect of this need for shade, which then shapes who we interact with and then shapes our social life more generally.
BRODIE: It seems like this will be an important lesson going forward as you know, temperatures continue to rise and the need for shade continues to become maybe more important, that humans, animals are able to respond to these kinds of environmental pressures with how we change to how we act and how we behave toward other people or other animals.
TESTARD: Absolutely. I think it's a really fundamental aspect. I think for the longest time, when we were thinking of how animals respond to climate change, we were thinking of where they move. So they typically, so if I live in a certain part of the mountain and it gets hotter, I'm gonna go up the mountain, so it gets to a cooler area, cooler space. But, that actually doesn't apply to a lot of species. There's a lot of species that can't really move to other places, they have to stick where they are.
So, another avenue to adjust to these new climatic conditions is actually social interactions and it's how they interact with other beings in their group, and that's, I think, what our study really revealed is that our social relationships is one, I think, core avenues that animals, including humans, will use to adjust to our changing environment.
