Peter Singer believes we are living through a "unique moment" in human history, one in which committed individuals can end poverty in the developing world once and for all. The proportion of people unable to meet their basic physical needs, writes Singer, is smaller today than at any other time in recent history, possibly ever, while the proportion of people with far more than they need is also unprecedented. Numerically, that's 1.4 billion poor compared to 1 billion rich people, and every day, while the wealthy spend money on things they could easily do without, 27,000 poor children — almost 10 million a year — die of preventable causes.

Singer, a philosopher and professor of practical ethics at Princeton University, thinks the plight of so many poor people amid such abundance is immoral, and he has written The Life You Can Save to explain why and, at the same time, shake the "haves" out of their moral lassitude. In it, Singer asks — and answers — such questions as, How far does our obligation to the poor go? How much does it cost to save a life? Which charities do it best? And how much is my fair share?

His answer to the last question is simple: Most people in the developed world could give 5 percent of their income to eradicate poverty in the developing world and still live comfortably. At the same time, the very rich — the top 5 percent of the population, whose average annual income ranges from $210,000 to $29.6 million — could give substantially more, from 10 percent to 33 percent, while still remaining very, very comfortable.

For those who find 5 percent a stretch, especially in this economic climate, Singer notes that Americans earning less than $20,000 a year actually give a higher percentage of their incomes — 4.6 percent — to charity than any other income group below the $300,000-a-year level. And he suggests that at the very least all of us could do "something that is significantly more than [we] have been doing so far."

But even for those who give generously, the truth is that when it comes to philanthropy, we tend to favor our families, our communities, and our country, in that order. That shouldn't come as a surprise. "We tend to assume that if people do not harm others, keep their promises, do not lie or cheat, support their children and their elderly parents, and perhaps contribute a little to needier members of their local community, they've done well," Singer writes. "If we have money left over after meeting our needs and those of our dependents, we may spend it as we please. Giving to strangers, especially those beyond one's community, may be good, but we don't think of it as something we have to do."

Such a view would have been familiar to Adam Smith. The eighteenth-century Scottish philosopher-cum-political economist had little time for "those whining and melancholy moralists, who are perpetually reproaching us with our happiness while so many of our brethren are in misery." To Smith, the status quo seemed "wisely ordered by Nature," since those who live far from us are people "we can neither serve nor hurt and who are in every respect so very remote from us."

It's no surprise that Singer, who wears his heart on his sleeve, sometimes comes across as the kind of "whining and melancholy moralist" that Smith disdained — never more so than when he calls giving to the arts "morally dubious," then concedes that in a world where more pressing needs have been met, giving to the arts could be seen as "noble." Singer also tends to view his fellow humans as either "good guys" or "bad guys." Among the former: Muhammad Yunus, the founder of Grameen Bank; economist Jeffrey Sachs, the driving force behind the UN Millennium Villages Project; and Bill Gates (though Singer can't resist sniping that the admirable Microsoft wunderkind could give more).

Although The Life You Can Save began as a series of lectures for Cambridge that evolved into a New York Times Magazine article, Singer acknowledges that he has been thinking, talking, and writing about how we should respond to hunger and poverty for more than thirty years. However, the book is not without problems. For instance, some of the examples he uses — Jessica McClure, the Texas toddler who was stuck in a dry well for two and a half days in 1987, and Kitty Genovese, who was stabbed to death near her apartment in New York City in 1964 as neighbors ignored her cries for help — are dated. The writing, despite the subject matter, lacks passion (is it a rule that philosophers have to be dispassionate?). And the final product is rather shapeless: what started out as an academic treatise, complete with twenty pages of footnotes, morphs, somewhat unconvincingly, into a roadmap to a new culture of giving and ends, briefly, as a seven-step how-to-guide to changing the world.

Still, what Singer proposes is both honorable and doable. If each of us gave just $200 a year, he suggests, the total raised would be $171 billion — roughly the amount needed annually to meet the UN Millennium Development Goals. Applied properly, the result would be 500 million fewer people living in extreme poverty, 300 million fewer people who no longer go to bed hungry, and 350 million fewer people lacking access to safe drinking water. In that brave new world, 650 million more people would have basic sanitation and, over the next decade, the lives of 30 million children would be saved.

It's enough to make you wonder: Who doesn't have $200 to help bring all that about?