Wetlands are areas of land that are covered by water all or part of the year. Throughout history, people have considered wetlands to be land that was wasted and could be put to better use. For this reason, from the time of the Romans, wetlands have been drained and filled so that the land could be used for human activity. Wetlands have been converted into farmland, city neighborhoods, industrial facilities, or garbage dumps. However, in recent years, scientists, environmentalists, and even politicians have begun to realize that wetlands are a valuable part of the environment, as well as a valuable resource for humans.

From a biological point of view, wetlands are not wastelands at all, but are among the most productive ecosystems in the world. They contain an immense variety of animal and plant species, which have evolved over millions of years and which depend on wetland ecosystems for their survival. The life cycles of all these species depend on the particular habitat of the wetlands, with its rich mixture of water and organic material from the breakdown of plants in water. The enriched material—known as detritus—feeds many small animals living in the water, such as aquatic insects, shell fish, and small fish. These small creatures, in turn, attract larger predatory animals that feed on them, including fish, reptiles, amphibians, birds, and mammals.

In recent years, city planners and politicians are beginning to realize that wetlands are valuable for another reason as well. In 2006, 13.3 inches (about 34 cm) of rain fell on the city of Newburyport in northeastern Massachusetts. In the neighboring city of Haverhill, only about 10 inches of rain fell. However, Haverhill suffered millions of dollars worth of damage from flooding, while Newburyport suffered almost no serious damage. Why such a difference? Both cities are built along the Merrimack River, but in Haverhill the area all along the river has been developed with housing, roads, and commercial buildings. In Newburyport, however, the area along the river has been left in its original state—marshland (wetlands). These wetlands gave the river waters space to spread out when there was a sudden increase in volume due to the rain. The wetland plants and soil also acted like a giant sponge to absorb water. In Haverhill, on the other hand, the water could not spread out, so it rose higher and higher, until it overflowed the banks and flooded areas of the city.

In these times of bombs and bio-warfare, it is harder than ever to dance to that old tune, “Just direct your feet to the sunny side of the street.” A study published last month in the British Journal of Psychiatry found that “depressive disorder is a highly prevalent condition in Europe.”

The report follows a decision by the European Commission to fund a comparative study of the prevalence’ of depression in the United Kingdom, Ireland, Norway, Finland and Spain. After questioning 8,850 adults in 1997 and ’98, the study concludes that just over 8.5% of them are depressed always or in episodes’. Generalized to the European Union as a whole, this is an epidemic that affects about 30 million people.

Women fare worse than men and, predictably, depression is generally less prevalent in rural than urban areas. But the most striking fact revealed by the study is the uneven geographic distribution. The study indicates that depression afflicts’ 17.1% of the urban population in the U.K. and 12.8% in urban Ireland. In rural parts of these countries and in both urban and rural Finland and Norway, the incidence ranges from 6.1% to 9.3%. But in urban Spain, the percentage drops to a mere 2.6. Why? Spain, where I live, has suffered from violent terrorism for more than 30 years; it has one of the E.U.’s highest unemployment rates, one of the worst records for industrial accidents, and is near the top of the tables for road fatalities, drug abuse and AIDS. It has Europe’s highest level of noise pollution.

But what Spain has in abundance compared with northern European nations—apart from more sun—is what the researchers in this study call social support structures. These structures have little to do with welfare or the number of doctors or psychiatrists. They are built on la familia.

One ironic fact about Europe’s north-south relative poverty gap is that lack of wealth tends to make families stay together. Offspring remain at home longer, frequently not being able to afford to move out until they are in their late 20s. Old people are not so easily parked in “homes.” Generalizing, in Spain, Portugal, Greece and Italy, family life probably runs deeper and longer than in the “better-off” north. Southerners fight and fall out like all families, but they tend to stick together against fate and the outside world. In Spanish hospitals, doctors have to push through ranks’ of relatives to get near the patient. Old people often die in the house now run by their children; before doing so, they are needed to mind grandchildren while both parents work. If a family member is depressed, he or she can find comfort and care in-house rather than paying a fee to talk to a professional. These qualities add up to a larger sense of solidaridad. As organ donors, Spaniards are unsurpassed’ in Europe; typically they respond generously to fund raisers.

Last week, I was in the street having an argument with a Spanish builder. A young mother with a newish baby in a pram happened to pass. The builder, Emilio, instinctively broke off his self-defense to talk to the kid, to feel its fat cheeks. The baby beamed,’ its mother started talking about how well it was taking the breast, Emilio assured her that the little fellow was a picture of health . . . and my rage fell apart. It was no diversionary’ tactic—I’d been familied.

The depression many Europeans have been suffering since Sept. 11 is no doubt harder to bear in cold Liverpool—where the British urban survey was based—than in the pleasant coastal city of Santander, where the Spanish researchers did their interviews. But a difference of depression of more than 14%? This is not explained by bluer skies or by the Anglo-Latin character divide.

A Spanish relative of my wife jokes that two things are best avoided: hot sun and families. But this 86-year-old widow passes hours on the phone with us each week. If we go out, the answering machine is often blinking when we return: “Where are you? Are you all right?” I used to feel harassed’ by this. Nowadays, the recorded voice makes me smile. A little bit of familia can go a long way to brighten this terrorized, often depressing world

In 1693, William Penn wrote that “the country life is to be preferred for there we see the works of God, but in cities little else than the work of man.” Most people at the time probably agreed with him. Less than 2 percent of the world’s population then were urban dwellers. But in 2018, about 54 percent of the world’s population lived in urban areas and more than 70 percent will do so by the end of 2030 (Haub, 2018; Linden, 2016; Fischer, 2015).

While urban populations have grown, cities themselves have changed. We can identify three periods in their history: the preindustrial, industrial, and metropolitan-megalopolitan stages.

The Preindustrial City

For more than 99 percent of the time that we humans have been on Earth, our ancestors have roamed about in search of food. They have hunted, fished, and gathered edible plants, but they have never found enough food in more than one place to sustain them for very long. They have had to move on, traveling in small bands from one place to another.

Then, about 10,000 years ago, technological advances allowed people to stop their wandering. This was the dawn of what is called the Neolithic period. People now had the simple tools and the know-how to cultivate plants and domesticate animals. They could produce their food supplies in one locale, and they settled down and built villages. The villages were very small—with only about 200 to 400 residents each. For the next 5,000 years, villagers produced just enough food to feed themselves.

About 5,000 years ago, humans developed more powerful technologies. Thanks to innovations like the ox-drawn plow, irrigation, and metallurgy, farmers could produce more food than they needed to sustain themselves and their families. Because of this food surplus, some people abandoned agriculture and made their living by weaving, making pottery and practicing other specialized crafts. Methods of transporting and storing food were also improved. The result was the emergence of cities.

Cities first arose on the fertile banks of such rivers as the Nile of Egypt, the Euphrates and Tigris in the Middle East, the Indus in Pakistan, and the Yellow River in China. Similar urban settlements later appeared in other parts of the world. The preindustrial cities were small compared with the cities of today. Most had populations of 5,000 to 10,000 people. Only a few cities had more than 100,000 and even Rome never had more than several hundred thousand.

Several factors prevented expansion of the preindustrial city. By modern standards, agricultural techniques were still primitive. It took at least 75 farmers to produce enough of a surplus to support just one city dweller. For transportation, people had to depend on their own muscle power or that of animals. It was difficult to carry food supplies from farms to cities, and even more difficult to transport heavy materials for construction in the cities.

Poor sanitation, lack of sewer facilities, and ineffective medicine kept the death rate high. Epidemics regularly killed as much as half of a city’s population. Moreover, families still had a strong attachment to the land, which discouraged immigration to the cities. All these characteristics of preindustrial society kept the cities small (Davis, 1955).

The Industrial City

For almost 5,000 years, cities changed little. Then their growth, in size and number, was so rapid that it has been called an urban revolution or urban explosion. In 1700, less than 2 percent of the population of Great Britain lived in cities, but by 1900, the majority of the British did so. Other European countries and the United States soon achieved the same level of urbanization in an even shorter period. Today, these and other Western countries are among the most urbanized in the world, along with many Latin American countries, which have become mostly urbanized in more recent years.

The major stimulus to the urban explosion was the Industrial Revolution. It triggered a series of related events, identified by sociologist Philip Hauser (2011) as population explosion, followed by population displosion and population implosion, and then by technoplosion. Industrialization first causes a rise in production growth, and the mechanization of farming brings about an agricultural surplus. Fewer farmers can support more people—and thus larger urban populations (population explosion). Workers no longer needed on the farms move to the city. There is, then, displacement of people from rural to urban areas (population displosion) and a greater concentration of people in a limited area (population implosion). The development of other new technologies (technoplosion) spurs on urbanization. Improved transportation, for example, speeds the movement of food and other materials to urban centers.

The outcome of these events was the industrial city. Compared with the preindustrial city, the industrial city was larger, more densely settled, and more diverse. It was a place where large numbers of people—with a wide range of skills, interests, and cultural backgrounds—could live and work together in a limited space. Also, unlike the preindustrial city, which had served primarily as a religious or governmental center, the industrial city was a commercial hub. In fact, its abundant job opportunities attracted so many rural migrants that migration accounted for the largest share of its population growth. Without these migrants, cities would not have grown at all because of the high mortality rate brought about by extremely poor sanitary conditions.

Metropolis and Megalopolis

Early in this century, the large cities of the industrialized nations began to spread outward. They formed metropolises, large urban areas that include a city and its surrounding suburbs. Some of these suburbs are politically separate from their central cities, but socially, economically, and geographically, the suburbs and the city are tied together. The U.S. Census Bureau recognizes this unity by defining what is called a Standard Metropolitan Statistical Area, which cuts across political boundaries. Since 1990, most U.S. residents have been living in metropolitan areas with 1 million residents or more (Suro, 2011).

In the United States, the upper and middle classes have usually sparked the expansion of cities outward. Typically, as migrants from rural areas moved into the central city, the wealthier classes moved to the suburbs. The automobile greatly facilitated this development. It encouraged people to leave the crowded inner city for the more comfortable life of the suburbs, if they could afford it. As the number of cars increased, so did the size of suburbs and metropolises. In 1900, there were only 8,000 cars in the United States; by 1930, the number had soared to more than 26 million. Meanwhile, the proportion of the U.S. population living in the suburbs grew from only 15.7 percent in 1910 to 49.6 percent in 1950 (Glaab and Brown, 1983).

Since 1950, virtually all the growth in metropolitan areas has occurred in the suburbs. During the 1960s, U.S. suburbs grew four times faster than inner cities, and stores and entertainment facilities followed the people there. Suburban jobs increased 44 percent, while inner-city employment dropped 7 percent. This pattern of suburban growth at the expense of the urban core continued in the 1970s and 1980s. Today, suburbanites outnumber city residents three to two (U.S. Census Bureau, 2003; Gottdiener, 2013; Jaaret, 2013).

As suburbs expand, they sometimes combine with the suburbs of adjacent metropolitan areas to form a megalopolis, a vast area in which many metropolises merge.

For hundreds of miles from one major city to the next, suburbs and cities have merged with one another to form a continues region in which distinctions between suburban, urban, and rural areas are blurred. The hundreds of miles from Boston to Washington, D.C., form one such megalopolis; another stretches from Detroit through Chicago to Milwaukee in the Midwest; and a third goes from San Francisco to San Diego.