Last Saturday evening my wife and I took our terminally ill cat to an animal hospital, where a veterinarian put him peacefully to sleep as he sat on my lap. I wasn’t really a cat lover when we adopted him seven years ago, but this unusually affectionate and communicative kitty cat converted me. I’m surprised how much I’m grieving for the loss of him.

Years before Toby came into my life I wrote a story for newspapers about domestic felines as deadly hunters of migratory songbirds. Several bird species, such as the Cerulean Warbler, are becoming vulnerable to extinction as their tropical-forest habitat disappears. A comparable threat on the other end of their migration is the predatory nature of pet cats, which by scientists’ estimates kill hundreds of millions of small animals every year.

So how do I square my concern about animal-killing cats with the affection I feel for one late individual of the species? Shouldn’t I be blaming cats for killing songbirds and threatening the survival of species not only of birds but of small mammals, amphibians, and reptiles?

Of course not. Cats do what evolution has programmed them to do. What has gone awry is not cats’ wants, which are natural, but their numbers, which are not. Nature is usually balanced in ways that make extinction a rare event—unless mortality levels reach levels that tilt the balance dangerously. That’s what has happened with pet cats. The United States alone is home to some 90 million. Most of them spend some time outdoors, and many of them kill. There never could be anywhere near this many domestic cats, obviously, if there weren’t even more human beings to care for them, just as my family did ours.

It’s a pint-sized example of a point I make in More: Population, Nature, and What Women Want. Environmental unsustainability tends to have much more to do with scale than with any essential aspect of our behavior. Cats aren’t bad because they kill birds; they’re just cats. But there are so many of them, and with cats, just as with humans, numbers matter. (In an endnote to Chapter 10, I note geographer Vaclav Smil’s estimate that livestock weigh 20 times as much as all the planet’s wild animals. Unfortunately, I couldn’t find a similar comparison between companion and wild animals.)

Since no one would seek a sudden reduction in the population of people—or of their pets—we often focus on modifying individual behavior to reduce environmental risks. In this case, the most important step the world’s hundreds of millions of cat owners can take to protect small animals is to keep their cats indoors. Fortunately for me, Toby had no interest in wandering outside, so he never killed anything bigger than the occasional bug that crawled past him on the floor. Our house was his whole world, which is why it feels so empty and sad as I write this post at home.

Read more at Island Interactive…

In my last blog post, I promised to wrestle with the time-honored Malthus Question: Does population growth outrun food supply? The old question is coming back as soaring food prices spark discontent, bread lines, and even riots around the world. I’ll try to answer this question decisively in the next 400 words.

Just kidding. Shelves heave under the weight of books that have grappled with the ideas of Thomas Robert Malthus since he first wrote in 1798. So maybe the answer will take more than one post.

Malthus posited that, “the power of population is…superior to the power of the earth to produce subsistence for man.” Conceiving children is always easy and fun, he argued, while growing food is hard-and gets harder as more people eat. (For more on this, see my book More: Population, Nature, and What Women Want, p. 162.)

First off, anyone who thinks that the Anglican rector and economist was known to his peers as “Thomas” Malthus should check out his Wikipedia entry. Wikipedia makes the point-as does More-that Malthus actually went by his middle name, Robert. His family called him, as mine calls me, Bob. His students at the training college for the British East India Company, where he taught as the world’s first political economist, affectionately dubbed him “Population” Malthus. Then they shortened that to Pop.

The fact that hundreds of population writers continue to call him Thomas makes clear that few have studied his life. That’s one reason I included a short biography of Malthus in More. Regardless of what you think of his ideas, it’s worth knowing a bit about the life and times of an influential thinker. And this one, after all, has been returning to the news-even to the front page of the Wall Street Journal, in a story inspired by the recent surges in energy and food prices. (The Journal’s classicdot-drawing of Bob, by the way, carried the caption “Thomas Malthus.”)

Here’s another name-related footnote on Pop Malthus, this one not in my book: His last name probably refers to a drinking establishment. For years, many people thought the rare and unusual surname couldn’t be English and suggested foreign-perhaps German-ancestry. In her magisterial biography Population Malthus, however, Patricia James makes the case that the name is thoroughly English and derives from-can you guess?-Malt House, a place to drink malt ale.

Okay, so it may take a few more posts to answer the Malthus Question. But at least we’re a bit closer to the man who inspired it. Would it help us deal with the population-food debate if we just think of him as “Bob, the bar guy”?

One of the dozens of countries around the world where hunger is back in the news is the Philippines, where soaring rice prices and long-standing reliance on imported food are raising an old question many people thought was buried for good: Does population growth eventually run into the limits of food production?

In More: Population, Nature, and What Women Want, I suggest this question will never be put to rest-not, at least, until populations stop growing. And, in fact, the recent surge in food prices is beginning to spur stories in the news media suggesting that population growth is indeed an important factor-perhaps especially in the Philippines. See, for example, this recent story by David Montero in The Christian Science Monitor. But let’s leave that debate aside for a later blog, and focus for a moment on another aspect of human numbers in the Philippines.

The country’s high population growth rate of 2 percent annually stems in large part from governmental hostility to modern contraception. That point is documented in another recent newspaper story, this one by Blaine Harden of The Washington Post. It’s hard to believe that in 2008 a national government would try to quell the use of oral contraceptive pills, IUDS, and condoms. Most women and their partners around the world use these devices, and most sexually active people in wealthy countries take their availability for granted.

But the Philippines’ national government follows closely and respectfully the dictates of the local Catholic hierarchy, which has condemned modern contraceptives as “chemical agents and mechanical gadgets that . . . have caused serious damage in family relationships.” One of Harden’s main sources for his story is a health organization whose staff asked not to be named because “they fear retaliation and harassment from officials in the national and city government, as well as from the Catholic Church.”

The main protagonist of the story is Maria Susana Espinoza, “who lives with her husband and children in a squatter’s hut in a vast, stinking garbage dump by Manila Bay.” Ms. Espinoza always hoped to have just two children but only learned details about contraception after her fourth child. “I don’t want any more children,” she told Harden. “Life is hard. Rice is expensive.”

It saddens me to read stories like this in today’s newspapers after chronicling similar tales spanning centuries in More. Ancient fears of sexuality and of women’s control over their own childbearing-see a chapter titled “Punishing Eve” for this history-still operate in some places in full force. As food and energy prices rise, the world’s fertility rate ought to be falling significantly, since many women quite naturally make reproductive calculations similar to those of Ms. Espinoza. Since women can’t postpone conceptions just by wishing, however, pregnancies happen despite their best intentions to wait for the right time. It’s an old story, but no less painful for that when it plays out today amidst growing hunger worldwide.

Author Robert Engelman Comments on Population on Earth Day

NEW ORLEANS—People walking around the Sheraton Hotel here are talking about population as if it were the most natural conversation in the world. The topic interests me, so I join in. As it happens, I’ve written a book on it, just published by Island Press, which I don’t shrink from mentioning. Just being here, though, reminds me that human numbers aren’t often talked about outside this hotel.

If there’s a time and place for talking population this is it: the annual meeting of the Population Association of America. The association’s demographers and public health specialists gathered this year in a city that lost about half its own residents to other places after a hurricane named Katrina. Panel topics ranged from that unprecedented urban population drop (the city’s population has since rebounded to around 70 percent of its pre-Katrina size) to the intriguing idea that the HIV/AIDS epidemic has peaked globally. While PAA members presented findings and partied at the Sheraton, people in the nearby streets of the French Quarter let the good times roll, as they usually do, with nary a thought of the number of us in the city, the country or the world.

But you don’t have to wander around the Big Easy to get a sense of how uneasy we are with population as an issue. Discomfort with the topic is everywhere, not least among environmentalists, who grapple daily with the ways human beings are altering the natural world and its life support systems. Who wants to reduce humanity to a number, or to see themselves as one? And population trends touch on some of the most sensitive issues in our experience: sex, race, childbearing, family size, immigration, abortion. Yet anyone paying attention to human-induced climate change or the ongoing surge in global energy and food prices must sometimes pause to think about just how many we are.

The fact that a few thousand professionals meet once a year to talk about population, at least, is a good sign. And this Tuesday is Earth Day, which on its launch back in 1970 integrated population into discussions about the environment. I’ll celebrate the day by discussing my book—titled More: Population, Nature, and What Women Want along with the author of a different take on population at the Woodrow Wilson International Center for Scholars in Washington.

World population has doubled since the first Earth Day. Does that mean worries about population growth were groundless, or that we’re in more peril today than in the past? And what does the future hold? From now through June, I’ll be weighing in from time to time with some thoughts on such questions on the Websites of both Island Press and the Worldwatch Institute. My book explores a few ideas that I hope will stimulate some conversation of its own, and maybe even a bit of hope for the future. I’ll welcome your comments.