Ecologists have long thought that growing human populations are a threat to the environment. But it turns out that sheer numbers of people may not be as important as how those people choose to live. You'll hear why in this Science Update.
The environmental cost of the nuclear family. I'm Bob Hirshon and this is Science Update.
Moving into your own place may be good for family relations, but bad for the environment.
New research by Michigan State University ecologist Jack Liu and his colleagues reveals that the number of households is increasing faster than the human population is growing.
When people talk about the human impact on the environment, they'll often talk about the human population size. And the number of households, basically, get ignored.
Instead of big, extended families all living under one roof, he says families are breaking up into smaller, independent units. That means more houses, requiring more land, energy, building materials, and even appliances.
For example, in a two person household, you may have a refrigerator. If you have four people in a household, you may have one refrigerator, also. So per person, the smaller household would need more energy.
Liu says as a result, humans are placing a greater strain on environmental resources. He says it's expected that the drop in household size alone will account for 233 million extra households by the year 2015. For the American Association for the Advancement of Science, I'm Bob Hirshon.
Making Sense of the Research
As we move into the 21st century, one of science's biggest concerns is the effect of the ever-expanding boundaries of human civilization on wildlife. Generally speaking, whenever humans move into an area, other animal and plant species suffer. That's because humans (especially present-day humans) demand a tremendous amount of natural resources. And thanks to modern technology, we're very good at getting those resources—often at the expense of other plants and animals that rely on them. What's more, humans dramatically alter the natural landscape by building homes, cutting down forests, damming rivers, and so on. Those changes inevitably affect the other species that live there.
Scientists who track the impact of human populations often focus on the total number of people in an area. But as you heard, Liu thinks that's only part of the picture. He and his colleagues (Gretchen Daily, Paul Ehrlich, and Gary Luck) have shown that overall, the number of households is growing faster than the human population itself. And that means that seemingly promising trends—for example, lower birth rates in most industrialized countries—may be offset or outweighed by the household boom.
Liu's team found that the growth in number of households was especially strong in what they called "hotspot countries": countries with a large variety of plant and animal species that are threatened by human activities. (This would include most of North America and Europe, for example.) And this couldn't be explained by increases in population alone. In fact, in a number of areas, the total population actually went down, but the number of households still went up, because people are living in smaller and smaller groups.
Why are people living in smaller households? Well, as we mentioned, people are having fewer children than before. Also, divorce is more common, which means that many families are split up between two or more homes. People have more money than they used to, which means they're less likely to share their living space, and they're living longer, which means they've got more time in an "empty nest" after the kids have grown. Finally, it used to be a lot more common for several generations (and maybe a few uncles, aunts, and cousins) to live together under one roof. Households like that are still the norm in some parts of the world, but not so much in the West, where the energy and resource demands of every home are also the highest.
These trends aren't going away anytime soon, so for scientists trying to soften the blow of the human impact on the environment, the problem will probably get thornier. But studies like this one can show them which numbers to keep an eye on.
Now try and answer these questions:
- What exactly do the researchers mean by "growth in number of households?" How is this different from growth in the total population?
- In some areas, the number of households increased, but the total population decreased. How can this be?
- Why are the researchers interested in the growing number of households and shrinking number of people per household? How do these trends impact the environment, compared with overall growth in population?
- Review the reasons behind the growth in number of households in the industrialized world. Assuming these trends continue, what can science—and citizens—do to counteract the impact of human households on the environment?
GLOBIO is an international project devoted to the study of human impacts on the biosphere.
Biodiversity is a Busch Gardens Tampa Bay educational resource about (guess what?) biodiversity.
Interpreting Population Statistics is a lesson plan from National Geographic Xpeditions that invites students to analyze birth rates, death rates, per capita income, life expectancy, and other aspects of human demographic studies.
View population density maps of the United States, courtesy of the University of Arkansas.