Children working in a London hosiery mill around the turn of the century. Did they have “Nature-Deficit Disorder (TM)”? Source.
Maybe you’ve heard of the scourge plaguing modern-day children, the one known as Nature Deficit Disorder (TM). You won’t find it in any of the standard diagnostic manuals used to identify true disorders, but the “disorder” arises, so the story goes, as a result of keeping children inside for fear of their safety and “stranger danger,” loss of natural surroundings in cities and neighborhoods, and increased attractions indoors that prevent spending time outdoors.
This “disorder” is supposed to be an effect of modern times, the combined effects of controlling and fearful parents along with the irresistible screen-based attractions indoors. As a result of this “disorder,” children can allegedly be susceptible to any number of ills, including less respect for and understanding of nature, depression, shorter life spans, and obesity.
Concerns like these, it seems, have arisen with the advent of each new technological advance. One wonders if the invention of the wheel raised alarms that children might move through their natural surroundings too quickly to take them in. At any rate, while the person who invented this disorder, Richard Louv, has actually trademarked the term, it doesn’t seem to have made a big splash in the scientific literature. Given that studies are lacking–i.e., completely absent–about “nature deficit disorder,” one thing we can do is take a look back at how children lived before the technological age to see if their indoor-outdoor lives and exposure to the natural world were substantially different.
Go far enough back in human history, and of course, we all spent a lot of time outside. But how did we spend our time with the rise of civilization? Children in agrarian societies then and now worked from dawn to dusk as part of the family to put food on the table. In such a position, they certainly had no lack of exposure to nature, although how much they appreciated that endless grind could be in question. That is, of course, if they didn’t die in infancy or early childhood, as a large percentage of them did in spite of all that fresh air and time outside.
But what happened with children and how they spent their time with the rise of towns and cities? In early times, many of those cities were walled compounds, not necessarily hives of scum and villainy, but generally stacks upon stacks of living quarters existing solely for functionality. Nature? Outside the walls, where danger–including the most extreme kind of “stranger danger”–lurked. Cities that lacked walls, as ancient Rome did for a long period, still were more focused on efficient crowding and function far more than on nature, with only the wealthy having gardens, the modern equivalent of today’s back yards. In general, there were people, there were buildings, and there were more people. Not wildly different from, say, Manhattan today–except for that whole natural jewel known as Central Park.
This piling on of people, brick, mortar, more people, and wood continued for children who didn’t live in agrarian societies. With the Industrial Revolution, what may have really been a nature deficit disorder for a child living, in, say, London, became a genuine threat to health. While they certainly didn’t have television to keep them indoors, they also didn’t have child labor laws. The result was that children who once might have been at work at age 4 in a field were now at work at age 3 or 4 in a factory, putting in 12 or so hours a day before stepping out into the coal-smoked, animal-dung-scented air of the city.
Child labor wasn’t something confined to Industrial Revolution Britain, and it continues today, both for agriculture and industry. I do wonder if the children harvesting oranges in Brazil feel any closer to nature than the children weaving carpets in Egypt. Likely, there are deficits more profound for them to worry about.
The trigger for this overview of whether or not things have really changed over recorded history in terms of children’s exposure to the natural world is this series of articles in the New York Times (NYT). In case you hit the paywall, it is the NYT’s “Room for Debate” series and includes four articles addressing whether or not nature shows and films connect people to the natural world or “contribute to ‘nature deficit disorder'” by keeping people glued to screens instead of being outside.
Louv, the coiner of “Nature deficit disorder TM”, is one of the four contributors to the debate. He argues that viewing nature documentaries can inspire us to go outside. He also thinks many of us grew up watching “Lassie” instead of the “Gilligan’s Island” my generation watched, but perhaps there’s not a huge difference between Timmy in the well and Gilligan in the lagoon and consequent outdoor inspiration. At any rate, Louv does argue in favor of viewing nature shows, although from a very first-world perspective (like the Romans and gardens, we don’t all have back yards, for example).
Perhaps the least-defensible perspective is the argument that Ming (Frances) Kuo, an associate professor of natural resources and environmental sciences, has to offer. She compares nature documentaries to “junk food” and offers the obvious: They’re no comparison for the real world. For some reason, she implies that someone has argued that when you have access to TV, you don’t need access to nature, saying, “Scientists have been discovering that even in societies where just about everyone has access to a TV, Internet, or both, having access to nature matters.” I honestly don’t think anyone’s ever argued against that.
Does “nature deficit disorder” exist and is indoor screen time with nature documentaries to blame? In addition to the historical observations I’ve made above suggesting that children from previous eras haven’t necessarily been wandering the glades and meadows like wayward pixies, all I have to offer is a bit of anecdata, and I’m curious about the experiences of others. Historical comparisons suggest that city-dwelling children are no more deficient nature-wise today than city-dwelling children of yesteryear. But do nature documentaries help… or hinder?
When I was young and watching too much “Sesame Street,” “Gilligan’s Island,” and “Star Trek,” the only nature show available to me was “Wild Kingdom” (Mutual of Omaha’s, natch). Other than that, we had nothing unless a periodic NOVA episode came on public television.
I was interested in science and nature, but acquiring knowledge outside of what I read in a book was difficult. As a resident of the great metropolis of Waco, Tex., yes, I had a natural world to explore, but let’s face it: The primates there weren’t that interesting, and bluebonnets get you only so far. I had no access to real-life live-motion visuals, auditory inputs, or information delivered in any form except what I could read in a book. Talk about sensory limitations.
These days, my children have a nature documentary library that extends to dozens and dozens of choices. And they have watched every single one, some of them repeatedly. That’s not to say that they don’t also have dozens of well-thumbed field guides and encyclopedias covering fossils, dinosaurs, plants, bugs, sharks, rocks–the usual obsessions of the young who are interested in nature. Our “movie nights” often kick off with a nature documentary, and our pick of choice will frequently be one involving narration from David Attenborough. My children want to be David Attenborough–so do I, for that matter–and I can’t recall ever really having that feeling about Marlin Perkins or Jim Fowler.
And the upshot of that access to an expanse of nature documentaries I never had is that their knowledge of nature is practically encyclopedic. I’m the biologist in the family–or at least the one who has the biology degree–but my children often know more than I do about a specific plant or animal or ecosystem or area of the world, all thanks to these documentaries they watch. And when we’re outside, they extrapolate what they’ve learned, generalizing it to all kinds of local natural situations.
Do children today just need to be moving around more, somewhere, somehow? Oh, yes. But watching nature shows hasn’t exacerbated some kind of “nature deficit” my children might have, Minecraft obsessed as they are. And these documentaries haven’t replaced “real” nature with televised nature. Instead, the shows have expanded on and given context to the nature my children encounter, wherever that is–city, country, farm, sky, ocean, parking lot, grocery store, or even inside their own home, which is currently the scene of a sci-fi-like moth infestation that has triggered much excitement. I’d hazard that far from causing a deficit, nature shows have given my children a nature literacy that was unknown in previous generations.
What is your take on nature deficits and nature documentaries?
First of all, in the context of science, you should never speak of evolution as a “theory.” There is no theory about whether or not evolution happens. It is a fact.
Scientists have, however, developed tested theories about how evolution happens. Although several proposed and tested processes or mechanisms exist, the most prominent and most studied, talked about, and debated, is Charles Darwin’s idea that the choices of nature guide these changes. The fame and importance of his idea, natural selection, has eclipsed the very real existence of other ways that populations can change over time.
Evolution in the biological sense does not occur in individuals, and the kind of evolution we’re talking about here isn’t about life’s origins. Evolution must happen at least at the populationlevel. In other words, it takes place in a group of existing organisms, members of the same species, often in a defined geographical area.
We never speak of individuals evolving in the biological sense. The population, a group of individuals of the same species, is the smallest unit of life that evolves.
To get to the bottom of what happens when a population changes over time, we must examine what’s happening to the gene combinations of the individuals in that population. The most precise way to talk about evolution in the biological sense is to define it as “a change in the allele frequency of a population over time.” A gene, which contains the code for a protein, can occur in different forms, or alleles. These different versions can mean that the trait associated with that protein can differ among individuals. Thanks to mutations, a gene for a trait can exist in a population in these different forms. It’s like having slightly different recipes for making the same cake, each producing a different version of the cake, except in this case, the “cake” is a protein.
Natural selection: One way evolution happens
Charles Darwin, a smart, thoughtful, observant man. Via Wikimedia.
Charles Darwin, who didn’t know anything about alleles or even genes (so now you know more than he did on that score), understood from his work and observations that nature makes certain choices, and that often, what nature chooses in specific individuals turns up again in the individuals’ offspring. He realized that these characteristics that nature was choosing must pass to some offspring. This notion of heredity–that a feature encoded in the genes can be transmitted to your children–is inherent now in the theory of natural selection and a natural one for most people to accept. In science, an observable or measurable feature or characteristic is called a phenotype, and the genes that are the code for it are called its genotype. The color of my eyes (brown) is a phenotype, and the alleles of the eye color genes I have are the genotype.
What is nature selecting any individual in a population to do? In the theory of natural selection, nature chooses individuals that fit best into the current environment to pass along their “good-fit” genes, either through reproduction or indirectly through supporting the reproducer. Nature chooses organisms to survive and pass along those good-fit genes, so they have greater fitness.
Fitness is an evolutionary concept related to an organism’s reproductive success, either directly (as a parent) or indirectly (say, as an aunt or cousin). It is measured technically based on the proportion of an individual’s alleles that are represented in the next generation. When we talk about “fitness” and “the fittest,” remember that fittest does not mean strong. It relates more to a literal fit, like a square peg in a square hole, or a red dot against a red background. It doesn’t matter if the peg or dot is strong, just whether or not it fits its environment.
One final consideration before we move onto a synthesis of these ideas about differences, heredity, and reproduction: What would happen if the population were uniformly the same genetically for a trait? Well, when the environment changed, nature would have no choice to make. Without a choice, natural selection cannot happen–there is nothing to select. And the choice has to exist already; it does not typically happen in response to a need that the environment dictates. Usually, the ultimate origin for genetic variation–which underlies this choice–is mutation, or a change in a DNA coding sequence, the instructions for building a protein.
Don’t make the mistake of saying that an organism adapts by mutating in response to the environment. The mutations (the variation) must already be present for nature to make a choice based on the existing environment.
The Modern Synthesis
When Darwin presented his ideas about nature’s choices in an environmental context, he did so in a book with a very long title that begins, On the Origin of Species by Means of Natural Selection.Darwinknew his audience and laid out his argument clearly and well, with one stumbling block: How did all that heredity stuff actually work?
We now know–thanks to a meticulous scientist named Gregor Mendel (who also was a monk), our understanding of reproductive cell division, and modern genetics–exactly how it all works. Our traits–whether winners or losers in the fitness Olympics–have genes that determine them. These genes exist in us in pairs, and these pairs separate during division of our reproductive cells so that our offspring receive one member or the other of the pair. When this gene meets its coding partner from the other parent’s cell at fertilization, a new gene pair arises. This pairing may produce a similar outcome to one of the parents or be a novel combination that yields some new version of a trait. But this separating and pairing is how nature keeps things mixed up, setting up choices for selection.
With a growing understanding in the twentieth century of genetics and its role in evolution by means of natural selection, a great evolutionary biologist named Ernst Mayr (1904–2005) guided a meshing of genetics and evolution (along with other brilliant scientists including Theodosius Dobzhansky, George Simpson, and R.A. Fisher) into what is called The Modern Synthesis. This work encapsulates (dare I say, “synthesizes?”) concisely and beautifully the tenets of natural selection in the context of basic genetic inheritance. As part of his work, Mayr distilled Darwin’s ideas into a series of facts and inferences.
Facts and Inferences
Mayr’s distillation consists of five facts and three inferences, or conclusions, to draw from those facts.
The first fact is that populations have the potential to increase exponentially. A quick look at any graph of human population growth illustrates that we, as a species, appear to be recognizing that potential. For a less successful example, consider the sea turtle. You may have seen the videos of the little turtle hatchlings valiantly flippering their way across the sand to the sea, cheered on by the conservation-minded humans who tended their nests. What the cameras usually don’t show is that the vast majority of these turtle offspring will not live to reproduce. The potential for exponential growth is there, based on number of offspring produced, but…it doesn’t happen.
The second fact is that not all offspring reproduce, and many populations are stable in size. See “sea turtles,” above.
The third fact is that resources are limited. And that leads us to our first conclusion, or inference: there is a struggle among organisms for nutrition, water, habitat, mates, parental attention…the various necessities of survival, depending on the species. The large number of offspring, most of which ultimately don’t survive to reproduce, must compete, or struggle, for the limited resources.
Fact four is that individuals differ from one another. Look around. Even bacteria of the same strain have their differences, with some more able than others to with stand an antibiotic onslaught. Look at a crowd of people. They’re all different in hundreds of ways.
Fact five is that much about us that is different lies in our genes–it is inheritable. Heredity undeniably exists and underlies a lot of our variation.
So we have five facts. Now for the three inferences:
First, there is that struggle for survival, thanks to so many offspring and limited resources. See “sea turtle,” again.
Second, different traits will be passed on differentially. Put another way: Winner traits are more likely to be passed on.
And that takes us to our final conclusion: if enough of these “winner” traits are passed to enough individuals in a population, they will accumulate in that population and change its makeup. In other words, the population will change over time. It will be adapted to its environment. It will evolve.
When Darwin presented his idea of natural selection, he knew he had an audience to win over. He pointed out that people select features of organisms all the time and breed them to have those features. Darwin himself was fond of breeding pigeons with a great deal of pigeony variety. He noted that unless the pigeons already possessed traits for us to choose, we not would have that choice to make. But we do have choices. We make super-woolly sheep, dachshunds, and heirloom tomatoes simply by selecting from the variation nature provides and breeding those organisms to make more with those traits. We change the population over time.
Darwin called this process of human-directed evolution artificial selection. It made great sense for Darwinbecause it helped his reader get on board. If people could make these kinds of choices and wreak these kinds of changes, why not nature? In the process, Darwin also described this second way evolution can happen: human-directed evolution. We’re awash in it today, from our accidental development of antibiotic-resistant bacteria to wheat that resists devastating rust.
Genetic drift: fixed or lost
What about traits that have no effect either way, that are just there? One possible example in us might be attached earlobes. Good? Bad? Ugly? Well…they don’t appear to have much to do with whether or not we reproduce. They’re just there.
When a trait leaves nature so apparently disinterested, the alleles underlying it don’t experience selection. Instead, they drift in one direction or another, to extinction or 100 percent frequency. When an allele drifts to disappearance, we say that it is lost from the population. When it drifts to 100 percent presence, we say that it has become fixed. This process of evolution by genetic drift reduces variation in a population. Eventually, everyone will have it, or no one will.
Gene flow: genes in, genes out
Another way for a population to change over time is for it to experience a new infusion of genes or to lose a lot of them. This process of gene flow into or out of the population occurs because of migration in or out. Either of these events can change the allele frequency in a population, and that means that gene flow is another was that evolution can happen.
If gene flow happens between two different species, as can occur more with plants, then not only has the population changed significantly, but the new hybrid that results could be a whole new species. How do you think we get those tangelos?
Horizontal gene transfer
One interesting mechanism of evolution is horizontal gene transfer. When we think of passing along genes, we usually envision a vertical transfer through generations, from parent to offspring. But what if you could just walk up to a person and hand over some of your genes to them, genes that they incorporate into their own genome in each of their cells?
Of course, we don’t really do that–at least, not much, not yet–but microbes do this kind of thing all the time. Viruses that hijack a cell’s genome to reproduce can accidentally leave behind a bit of gene and voila! It’s a gene change. Bacteria can reach out to other living bacteria and transfer genetic material to them, possibly altering the traits of the population.
Sometimes, events happen at a large scale that have huge and rapid effects on the overall makeup of a population. These big changes mark some of the turning points in the evolutionary history of many species.
The word bottleneck pretty much says it all. Something happens over time to reduce the population so much that only a relatively few individuals survive. A bottleneck of this sort reduces the variability of a population. These events can be natural–such as those resulting from natural disasters–or they can be human induced, such as species bottlenecks we’ve induced through overhunting or habitat reduction.
Founder effect: starting small
Sometimes, the genes flow out of a population. This flow occurs when individuals leave and migrate elsewhere. They take their genes with them (obviously), and the populations they found will initially carry only those genes. Whatever they had with them genetically when they founded the population can affect that population. If there’s a gene that gives everyone a deadly reaction to barbiturates, that population will have a higher-than-usual frequency of people with that response, thanks to this founder effect.
Gene flow leads to two key points to make about evolution: First, a population carries only the genes it inherits and generally acquires new versions through mutation or gene flow. Second, that gene for lethal susceptibility to a drug would be meaningless in a natural selection context as long as the environment didn’t include exposure to that drug. The take-home message is this: What’s OK for one environment may or may not be fit for another environment. The nature of Nature is change, and Nature offers no guarantees.
Hardy-Weinberg: when evolution is absent
With all of these possible mechanisms for evolution under their belts, scientists needed a way to measure whether or not the frequency of specific alleles was changing over time in a given population or staying in equilibrium. Not an easy job. They found–“they” being G. H. Hardy and Wilhelm Weinberg–that the best way to measure this was to predict what the outcome would be if there were no change in allele frequencies. In other words, to predict that from generation to generation, allele frequencies would simply stay in equilibrium. If measurements over time yielded changing frequencies, then the implication would be that evolution has happened.
Defining “Not Evolving”
So what does it mean to not evolve? There are some basic scenarios that must exist for a population not to be experiencing a change in allele frequency, i.e., no evolution. If there is a change, then one of the items in the list below must be false:
·Very large population (genetic drift can be a strong evolutionary mechanism in small populations)
·No migrations (in other words, no gene flow)
·No net mutations (no new variation introduced)
·Random mating (directed mating is one way nature selects organisms)
·No natural selection
In other words, a population that is not evolving is experiencing a complete absence of evolutionary processes. If any one of these is absent from a given population, then evolution is occurring and allele frequencies from generation to generation won’t be in equilibrium.
Arguably the most famous of the egg-laying monotremes, the improbable- seeming platypus. License.
One of the best examples of the influences of environmental pressures is what happens in similar environments a world apart. Before the modern-day groupings of mammals arose, the continent of Australiaseparated from the rest of the world’s land masses, taking the proto-mammals that lived there with it. Over the ensuing millennia, these proto-mammals in Australiaevolved into the native species we see today on that continent, all marsupialsor monotremes.
Among mammals, there’s a division among those that lay eggs (monotremes), those that do most gestating in a pouch rather than a uterus (marsupials), and eutherians, which use a uterus for gestation (placental mammals).
Elsewhere in the world, most mammals developed from a common eutherian ancestor and, where marsupials still persisted, probably outcompeted them. In spite of this lengthy separation and different ancestry, however, for many of the examples of placental mammals, Australiahas a similar marsupial match. There’s the marsupial rodent that is like the rat. The marsupial wolf that is like the placental wolf. There’s even a marsupial anteater to match the placental one.
How did that happen an ocean apart with no gene flow? The answer is natural selection. The environment that made an organism with anteater characteristics best fit in South America was similar to the environment that made those characteristics a good fit in Australia. Ditto the rats, ditto the wolf.
When similar environments result in unrelated organisms having similar characteristics, we call that process convergent evolution. It’s natural selection in relatively unrelated species in parallel. In both regions, nature uses the same set of environmental features to mold organisms into the best fit.
Note: This explanation of evolution and how it happens is not intended to be comprehensive or detailed or to include all possible mechanisms of evolution. It is simply an overview. In addition, it does not address epigenetics, which will be the subject of a different explainer.
Battling the uninformed, insurance companies, and your own compulsions
[Ed. note: This post is the first in our series, “I Am Mental Illness,” bringing you personal experiences living with a mental illness. It’s likely that no single one of us lives a life untouched by mental illness, our own or that of someone we know. Yet in spite of their high prevalence, these disorders remain stigmatized and undersupported. To learn more about mental illness, you can start with the National Alliance on Mental Illness website. To learn more about anorexia and other eating disorders, you can start with this guidebook from the National Institute of Mental Health. Double X Science has previously featured a post by Harriet Brown describing the effects of family-based treatment for anorexia.Continue reading →
Climate vs weather: Do you know the difference? This video explains it oh so very clearly.
Vaccinating children is a social responsibility, like driving on streets and not sidewalks, not stabbing people, and giving pedestrians the right of way at street crossings. When you choose not to do it, you endanger others (see “measles,” above).
Can moderate red wine consumption cut breast cancer risk? This study found that red wine consumption altered hormone levels in the blood in a pattern that suggests it might halt the growth of cancer cells. Not anything definitive.
We’ve been reading a lot lately about these great ways to trick picky eaters into eating. We know from experience that some picky eaters are untrickable. This scimom tells us what one of the latest studies really means.
Anyone who has ADHD—attention-deficit/hyperactivity disorder—can tell you the stories. Stories of getting into constant trouble, hearing “sit down, sit still, be quiet” repeatedly, endlessly, feeling the urge to move, touch, jump, talk, roll, do anything but sit quietly at a desk, working on math. And, as anyone who has ADHD can also tell you, these traits often don’t exactly help you get ahead in modern society. School requires stillness, attention, focus on pencil and paper work. Most jobs require focus, attention, sometimes an ability to tolerate the sheer boredom of four walls of a grey cubicle for eight hours each day. Most people would struggle with that, but with attention deficit, it’s more than a struggle.
A cubicle environment obviously is probably not the best place for someone with ADHD, although it may be beneficial in less boxy workplaces. And school can be a long, troubling, negative process, as well. People used to blame the parents of children with this disorder, laying the cause of ADHD at the feet of poor parenting–and some are still trying to lay that blame. Science has something else to say about it, having demonstrated that genes are actually the primary contributors to ADHD, specifically genes that encode proteins whose job is to “receive” messages from a brain chemical called dopamine.
Dopamine signaling underlies all kinds of behaviors, but primarily it is known for its involvement in reward pathways, novelty seeking, and addiction. Specific forms, or alleles, of dopamine receptor genes have been strongly associated with ADHD, and this disorder can be viewed in many cases as a constant search for reward and novelty, a search that can translate as inattentiveness or hyperactivity.
Given that this dopamine-based manifestation is rooted in genes, the question arises of why it has persisted in humans throughout our evolution. If we look around at modern society, it’s easy to see that ADHD behaviors generally are not conducive to being one of the “fittest” in many situations that take up most of our time. Yet, there has been enough associated advantage for these gene forms to persist and allow their carriers to reproduce and pass them along to offspring.
And that’s where we need to think in nature’s evolutionary terms. Modern society is just that—modern. This way of life has only been around for, at most, a few thousand years, which can be a blink of an eye for processes of natural selection. Dial back time about 10,000 years or 20,000 years, and you’ll be hard pressed to find any humans living in an environment anything remotely like a cubicle.
Natural selection results from the interaction of genes and environment, and the “selection” Nature’s making is for an individual’s genetic makeup to have some representation in future generations. To look at this process through Nature’s lens, take the gene forms associated with ADHD and place them in a different environment and ask the question: Do they help or hurt or make no difference at all?
This question is exactly what researchers addressed when they looked at the effects of an ADHD-related gene form on a group of nomadic people, the Ariaal, in Kenya. Some members of this population had, in only the last few decades, made a transition to a sedentary, city-type lifestyle. Others continued to live the fast-moving, nomadic existence of their herding ancestors.
Researchers looked at a version of a dopamine receptor called DRD4-7R, which also has been implicated in autism symptoms in people with ADHD. They found that city dwellers with this form of the gene didn’t fare as well in health as their sedentary cousins without it. But the Ariaal who continued their nomadic existence and carried the 7R form of the gene fared better than those nomadic tribesmen without it. To assess health, the researchers looked at body mass index and other factors. The results suggest that there might be some benefit to ADHD in the backdrop of a nomadic culture. although a more recent analysis of several studies together suggests a different form of this receptor may have an ADHD association (this kind of study, called a meta-analysis, doesn’t provide new data but synthesizes existing data).
Regardless of which gene forms are involved, you can imagine that in a nomadic culture, it might be useful to be always looking around, seeking novelty, thriving on the rewards of changing behaviors, defending food, and being always on the move. Someone with ADHD likely would be far better fit for this kind of lifestyle than would the best desk jockey in the world. This interesting study demonstrates that when it comes to some of the neurological developmental manifestations we call “disorders,” how negative or positive they are may be a matter of environment.