If you live in a big city, you may have noticed new buildings popping up — a high-rise here, a skyscraper there. The concrete jungles that we’ve built over the past century have allowed millions of us to live in close proximity, and modern economies to flourish. But what have we given up by moving away from the forest environments in which humans first evolved? This week, we discuss this topic with psychologist Ming Kuo, who has studied the effects of nature for more than 30 years.
The transcript below may be for an earlier version of this episode. Our transcripts are provided by various partners and may contain errors or deviate slightly from the audio.SHANKAR VEDANTAM, HOST: This is HIDDEN BRAIN. I'm Shankar Vedantam.(SOUNDBITE OF MUSIC)VEDANTAM: If you're living in a city, you may have noticed new buildings popping up - a high-rise here, a skyscraper there. These concrete jungles make urban living possible. They allow millions to live together in close proximity and allow modern economies to flourish. But is there something important missing in this picture?(SOUNDBITE OF BIRDS CHIRPING)VEDANTAM: For most of the last 2 million years, humans lived in a natural world, relying on nature for food and shelter. The amount of time we've spent in urban dwellings is a small sliver of the total time humans have spent on Earth. When you look at it this way, our shift from forest life to freeways and overflowing cities has been very recent and very dramatic. Today on HIDDEN BRAIN, we explore how this shift in the way we live might be having powerful effects on our lives and our well-being.MING KUO: We are overlooking a crucial ingredient in the urban fabric, which is nature and elements of nature. So parks and greenery turn out to be not just something that brightens our lives but turns out to be really functional. It helps us be our better selves.VEDANTAM: Ming Kuo has been studying the effects of nature on humans for more than 30 years. She works at the University of Illinois Urbana-Champaign. Early in her career, Ming studied research looking at the well-being of animals in zoos. Researchers found that even what animals were provided all the basics of food, safety and shelter, they often failed to thrive.KUO: It turns out that zoo animals, first of all, are extremely expensive. They die at fairly alarming clips. And so biologists have studied animals in the wild, and one of the ideas that they have is that there's this thing called habitat selection theory, which is that we are - we're wired for whatever habitat we evolved in. And so there seems to be this general kind of rule that animals who are in their, quote, unquote, "natural habitats" will do much better. They thrive both in terms of physically and psychologically and in terms of their social behaviors.VEDANTAM: So if zoo animals thrive in their natural habitat, some researchers have asked, could this also be true for humans? Given that humans first evolved in the forests of Africa, could it be that depriving humans of this natural environment has effects similar to housing a zebra in a cage? We'll get to Ming's answer to that question in a moment. But first, it's important to understand how she came to be studying this in the first place. She wasn't particularly interested in the benefits of greenery and nature. She was interested in the negative effects of noise and crowding.KUO: The way I got into the research on the effects of the natural environments on people was I was interested in the dark side of the environment. I was interested in how violent or dangerous or, you know, bad urban environments had detrimental effects on people. And I only got into this by accident, and then I only came up with this view of the effects of nature through the data. So I have been kind of dragged (laughter) - I have been dragged into this all the way kicking and screaming. I did not have that view of people that I set out to test. I came upon that view because I was trying to make sense of what the findings have been.VEDANTAM: I'm glad you said that because, you know, this idea that people need greenery or that greenery is essential to, you know, human satisfaction, well-being, thriving - you know, when I first heard that, I sort of said, you know, that sounds like a really feel-good idea that I could, you know, hear on a New Age...KUO: (Laughter).VEDANTAM: ...Magazine.KUO: Right.VEDANTAM: I find it appealing that, in some ways, you were a skeptic yourself - that, for a long time, you found this idea to be sort of squishy.KUO: Yeah. I think, like a lot of people, I thought of the environment as, you know, trees, grass, gardens, flowers. I thought of that as kind of a nice amenity, you know? They're not functional (laughter), right? They're not what we need. And so it's only when you look at the patterns of what people are like with more and less access to nature that you start to see this pattern - where, gosh, you know, we see the same thing in humans that we see in zoo and lab animals, which is the wonderful quote from E.O. Wilson - is that organisms, when housed in unfit habitats, undergo social, psychological and physical breakdown.And we are seeing precisely that in people. So when you have people who are - who have a certain amount of access to nature and then you give them a bit more, you see better social functioning. You see better psychological functioning and better physical health.VEDANTAM: In some ways, this argument is saying that humans today - or many humans today - are living in the kind of conditions that we used to keep zoo animals in 50 years ago.KUO: I mean, obviously, we are doing better by a lot of humans than most zoo animals did in the old days. But I think we are, to some extent, housing Homo sapiens with that same functional view that, OK, well, as long as they have shelter, water, food, safety, you know, that's pretty good. That should do it, right? And then anything else beyond that is sort of a plus and it's nice. It's yummy (laughter). But it's not - it's not important.VEDANTAM: I want to take you methodically through some of the empirical evidence that persuaded you that this was more than just a feel-good theory. And I'm wondering if we could start with the studies that you and others have conducted in Chicago. Walk me through this research starting with the study that you conducted at the Robert Taylor Homes.KUO: Sure. So Robert Taylor Homes is a - or was a series of 16 10-story buildings sort of along a particular corridor in Chicago. And they were originally designed with greenery all around them. But over time, as you can imagine, if you have a ton of kids...(SOUNDBITE OF CHILDREN LAUGHING)KUO: ...Running around in a courtyard space - you don't have much money for maintenance - if it rains, they get mud everywhere, and the grass gets trampled, and it very quickly tends to die. And so there are very few cases in which the building managers didn't end up just paving over what used to be grassy areas. And so if you pave over those areas, you take the trees out, then you just have asphalt. So we had this beautiful kind of experiment where people are randomly assigned to different buildings that are identical. And some of those buildings have a bit of trees and grass around them, and some of them don't. And we just went about studying what the outcomes were in those different buildings.VEDANTAM: And what did you find?KUO: Well, we looked at a bunch of things, but I think the sort of short answer is we found - (laughter) we found social breakdown in buildings without trees and grass around them. That is to say, when we asked people did they know their neighbors, did they speak to their neighbors, do they know them on first-name basis, could they rely on their neighbors for, you know, for a favor, to take care of their kids if they had an emergency, then the people in the buildings with a bit of greenery were much more likely to say yes. We also found that the folks who are in the less green buildings are reporting more aggressive behaviors.And, of course, we had reasons to think this might be the case according to theories. So there's this attention restoration theory, which says that when people are - don't have access to nature, they're going to be more mentally fatigued. So when you're mentally fatigued, you're also less good at handling difficult social situations. And so we thought, OK, if nature is helpful for rejuvenating people from mental fatigue, then folks in buildings who don't have any access to nature are going to be that much more fatigued and that much more irritable and that much more difficulty handling conflict in a productive way. And what's - of course, when we got these findings, we were kind of like whoa, you know. I mean, I know the theory predicts this, but I didn't think we'd actually get it.(SOUNDBITE OF MUSIC)KUO: And so I did a follow-up involving Chicago Police Department crime statistics. They were very good about giving us two years' worth of crime statistics from another development. We wanted to see if this general effect showed up in other Chicago public housing developments. So we looked at a low-rise one instead of high-rise, and we see the same pattern in police records of crime.VEDANTAM: So it can't just be that people living in closer proximity to trees maybe have rosier memories of their interactions with others. In fact, you know, hypothetically, you're seeing maybe the same amount of disagreement and conflict, but people are just remembering it differently.KUO: Right.VEDANTAM: You're saying the police records, in some ways, provide an objective measure that there actually is less conflict in these buildings.KUO: Right. Right. Exactly.VEDANTAM: So I'm wondering about other confounding things in the study. I mean, is it possible that apartment buildings with more green space had different numbers of people living in them? You know, I know the buildings themselves were identical, but is it possible there were fewer people for some reason living in the greener buildings and what you're measuring is really related to crowding and not related to green space?KUO: Good question. But as you remember, those were the variables I cared about (laughter) right? So I wondered about is there more noise, or was there more crowding? What else is going on in these buildings? And so because I was interested, I made sure to measure all of those things. And it turns out that those did not explain the relationship. So let's just take crowding as an example. If there was crowding, then it didn't fit the pattern that the violence fit, or it didn't fit the pattern of the green space, or both.VEDANTAM: I understand there's been research done out of Columbia University and the University of Pennsylvania that has explored what happens when you green parts of a city - add more trees and grass to parts of a city - that this has measurable effects, not just on the quality of life but even on the crime rate.KUO: Right. And the numbers are really pretty startling. So they - these researchers worked with the city to coordinate their vacant lot program. And basically, what they did was they designated a bunch of vacant lots as eligible for "cleaning and greening," quote, unquote. So that involves taking out all the trash - the little bits of glass, cigarette butts - cleaning it up, putting in some turfgrass, you know, a nice panel of lawn, and then some trees.(SOUNDBITE OF MUSIC)KUO: So fairly inexpensive intervention, and they randomly assigned which lots would get this intervention and which ones would not. And then they tracked what happened in those lots afterwards. And it turns out that in the lots that receive this intervention, gun assaults go down - by police records - 9.1 percent, which is really, you know, like, (laughter) boy, you know, if we have anything that cost any amount of money that can reduce gun assaults by 9 percent in a city, you know, any mayor in the U.S. is going to trumpet that. And we see similar patterns for burglaries and other complaints. So it was a very exciting finding.VEDANTAM: If I recall correctly, wasn't there a time, Ming, when actually police had the opposite intuition? They actually thought that having trees and bushes could actually increase crime because it gave, you know, bad guys, you know, places to hide. And, in some ways, it made surveillance easier if you actually eliminated all of that and it's just that open - you know, open lots or just, you know, things paved over.KUO: Right. There was that belief, and, in fact, there is something to that intuition, but it's fairly limited. So if you have a lot of basically brush and undercover, that can, in certain circumstances, particularly in park settings (laughter), depending on lines of visibility, then yes, a large bush can provide a place to hide drugs or a gun or whatever. And, at the same time, what we see is that if you have limbed-up trees - trees that do not block visibility at eye level - the consistent finding is more trees, less crime.(SOUNDBITE OF MUSIC)VEDANTAM: What was your reaction, Ming, as a researcher in some ways who wasn't necessarily looking for this finding and in some ways, as I'm detecting, was sort of somewhat skeptical about sort of the overall (laughter) relationship between nature and these positive things? What was your reaction when you got these results?KUO: I mean, to be a scientist - to be a good scientist is to be a skeptic, you know? So even when you have a theory that's your pet theory - and this was by no means my pet theory - your job is to try to figure out, is there some way this - we could have found this without my pet theory being true?And so I'll tell you a related story. My old adviser, Rachel Kaplan, is one of the giants in this field. She did her work for decades in a building at the University of Michigan that faces onto a brick interior courtyard - just bricks and gravel at the bottom (laughter). So she spends her career there - 30, 40 years, I don't know how many years, right? And then, over time, she does stupendous work, and the university finally decides to give her a named chair - a professorship - sort of very fancy position.And, at the same time, they're renovating the building, and they move Rachel into a third-floor corner office in the trees. It's right in the canopy, and her office is all windows. And she says to me, you know, I have been studying this for how many decades, and now I know it's really true.(LAUGHTER)VEDANTAM: This is HIDDEN BRAIN. I'm Shankar Vedantam. For years, Ming Kuo has studied how nature affects us and how the lack of access to nature can lead to crime and social breakdown. It turns out this is only part of the story. There's also a relationship between nature and our physical and mental health. Ming says there seems to be a connection between greenery and health markers for obesity, hypertension and diabetes.KUO: So I did a review of the scientific literature, and I found every bit of evidence I could that tied greenery to long-term health outcomes. So, for instance, one of the things we find is that when you look out at a green landscape, even from indoors, your heart rate will go down, and you'll change from sympathetic nervous activity over to parasympathetic nervous activity, which is basically going from what we call fight or flight into tend and befriend mode. So it has these very systematic physiological impacts on us, which we also know have long-term health outcomes associated with them. And I found, you know, dozens of health outcomes where long-term health outcomes had been tied to contact with nature. And all of those studies - I threw out anything that didn't take into account socioeconomic status.(SOUNDBITE OF MUSIC)KUO: It is no surprise that we would find rich people tend to have greener neighborhoods and better health outcomes. I was interested in let's take two people - same income, same life circumstances except for the greenery, and what do we see in terms of health outcomes there?VEDANTAM: Let's talk a little bit about the socioeconomics of this. As you and others have pointed out, there is an enormous disparity in many countries not just between the rich and the poor but in neighborhoods that are green and neighborhoods that are not green. And, in many ways, this lines up with disparities between the rich and the poor. Rich neighborhoods tend to be greener. Poor neighborhoods tend to be less green.KUO: Right.VEDANTAM: How much of what you are seeing - is it possible that some of this is actually just related to differences in wealth that then produce all kinds of other, you know, health consequences? Or do you think this is actually connected just to the greenery itself?KUO: Well, that's that's exactly the concern, right? We already knew that wealthier people have better health outcomes and more greenery. So then how do you compare? And, basically, what you do is you look for people who have the exact same person A in this green neighborhood and person B in this not green neighborhood. You want to make sure persons A and B have the same income. So all of these comparisons in this review I did, we're taking that into account.VEDANTAM: One of my favorite studies in this area comes from an analysis of pharmacies in London and the medications they dispense. And there's a connection between this and the amount of greenery in different neighborhoods in London. What did the study find?KUO: So pharmacies in London are neighborhood-based, so pretty much people go to the pharmacy that's in their neighborhood. And they know how green it is around each pharmacy, and they also know how many people live there, how many people the pharmacy serves, and they know prescriptions for mood-related - you know, anxiety disorder medications and depression medications. And they just compared for pharmacies that compare the same number of people with the same rough income, how many more mood medications are they prescribing? And it's substantially larger the less greenery is around the neighborhood.(SOUNDBITE OF MUSIC)VEDANTAM: There also appears to be a relationship between greenery and the strength of our immune systems. After people spend several days in nature, researchers find measurable increases in what are known as natural killer cells.KUO: After a three-day weekend in a forest preserve - that boosts natural killer cells on average by 50 percent. And a three-day weekend in a nice urban area, it turns out, doesn't do anything for your natural killer cells. And then, if I come (laughter) knock on your door 30 days later after your three-day weekend, and I say, can I have another sample of your blood, please, and you give it to me, it will show that you are still roughly 24, 25 percent above your baseline number of natural killer cells, So it's a big effect, and it lasts for a really long time.VEDANTAM: What do you think is going on here, Ming? I mean, is it just the things we see when we're out in nature? Is it things we smell? Is it just the experience of being out in nature? Is it the perception? Is there - what's driving these effects, do you think?KUO: Well, the answer is yes (laughter). So it turns out that if we take people and put them in a lab, and we just show them pictures of nature, and we watch what happens to their blood pressure and their nervous system activity, we can see them become more calm. So just the visual is enough. Similarly, if I take you into a lab, and I spritz what we call phytoncides, which are these essential aromatic compounds that you associate with woods - so if I spritz you with phytoncides - you don't have to be in a pine forest - I can see changes in your natural killer cells and in your bloodstream.VEDANTAM: So, of course, if you're a mad scientist, you would say, well, really all you have to do is make sure that people's screen savers are set to pictures of forests...KUO: (Laughter).VEDANTAM: ...And you sort of pipe in some, you know, sounds of the forest over the public address system, and you - you know, you spritz the air with some eucalyptus, and you're done.KUO: Well, you will have a measurable positive effect. If I give you vitamin D, and I give you vitamin A, then that takes care of your D and A deficiency, but it doesn't take care of your B and C deficiencies. So nature seems to be like a multivitamin.(SOUNDBITE OF MUSIC)KUO: You can get different benefits from different kinds of exposure, you know, right - the spritzing versus the visual versus the smell or whatever. But to get all of them, you kind of have to be there.VEDANTAM: So I'm wondering, how do you take this multivitamin every day, Ming? You've - you started out as a skeptic, and you have gradually come to be persuaded by the evidence. Have you found ways to actually apply these insights to your own life?KUO: I live about a 10-minute walk from the university, from the campus, and I do something which probably looks completely ridiculous to the average person driving by me. I walk to and from school with my eyes in the canopy. I - (laughter) I fly through the trees on the way to school, and I fly through the trees on the way back from campus. And I have - so my head is up. I'm probably at danger of tripping. I look ridiculous. But it makes a real difference for me, and once I started adopting it, I have become hooked.(SOUNDBITE OF BIRDS CHIRPING)VEDANTAM: Ming Kuo studies the effects that nature has on human beings. She's a researcher at the University of Illinois at Urbana-Champaign.Ming, thank you so much for joining me today on HIDDEN BRAIN.KUO: Thank you so much.(SOUNDBITE OF MUSIC)VEDANTAM: This week's show was produced by Thomas Lu and edited by Tara Boyle. Our team includes Rhaina Cohen, Jenny Schmidt, Parth Shah and Laura Kwerel. We also welcome a new intern today, Camila Vargas.Our unsung hero is Emily Blackman, who oversees events at the Chesapeake Bay Foundation. We recently had a staff retreat at the foundation's headquarters, and Emily made sure everything ran smoothly. Her work gave us a chance to take a breath and connect with nature and with each other. It was a wonderful day, and we're truly grateful.For more HIDDEN BRAIN, you can find us on Facebook and Twitter. If you enjoyed today's show, please share it with one friend, perhaps on a nice walk in the woods. I'm Shankar Vedantam, and this is NPR.(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.