“The battle to feed all of humanity is over. In the 1970s, hundreds of millions of people will starve to death in spite of any crash programs embarked upon now. At this late date nothing can prevent a substantial increase in the world death rate.” Thus began The Population Bomb, a 1968 book by Stanford University professor Paul Ehrlich. Since those now infamous words were written, world population has doubled from 3.5 billion to 7 billion, inflation-adjusted average annual income per person has risen from $3,147 to $5,997, and life expectancy at birth has increased from 59 years to 69 years.

The world’s daily caloric intake per person rose from an average of 2,610 in 1990 to 2,790 in 2006. That increase was not driven by horizontally challenged Westerners alone. In sub-Saharan Africa, the caloric intake increased from 2,290 to 2,420 in just 16 years. To put these figures in perspective, the U.S. Department of Agriculture recommends that adult men eat between 2,000 and 2,500 calories a day and women between 1,800 and 2,300 calories a day.

Often seen as hopeless, Africa has made other significant gains. In spite of wars, massive economic mismanagement and the ravages of AIDS, the continent’s population has more than trebled — from 280 million to 854 million — since 1968, and life expectancy has increased from 44 years to 54 years.

According to the latest World Bank research, global poverty is declining rapidly. In 1981, 70 percent of people in poor countries lived on less than $2 a day, while 42 percent survived on less than $1 a day. Today, 43 percent live on less than $2 a day, while 14 percent survive on less than $1. “Poverty reduction of this magnitude is unparalleled in history,” wrote Brookings Institution researchers Laurence Chandy and Geoffrey Gertz in a recent paper. “Never before have so many people been lifted out of poverty over such a brief period of time.”

It is not only material well-being that is improving. Groundbreaking research by professor Steven Pinker of Harvard University shows a propitious decline in physical violence. According to Mr. Pinker, “Violence has been in decline for thousands of years, and today we may be living in the most peaceable era in the existence of our species.” Indeed, studies have shown that hunter-gatherer societies experienced about 524 violent deaths per 100,000. The rate of violent deaths in the war-torn 20th century, by comparison, amounted to a mere 60 per 100,000. To quote British Prime Minister Harold Macmillan (1957), we “have never had it so good.”

Historical evidence makes a potent case for what writer Matt Ridley called “rational optimism.” Optimism, alas, is the last thing to look for in a new documentary produced by Martin Scorsese that opened in American cinemas on April 6. Called Surviving Progress, the movie rehashes many of the ideas that doomsayers like Mr. Ehrlich have been peddling for some time — including the dangers of overpopulation, overconsumption, destruction of natural resources, capitalist greed and cultural decline.

If the reception of previous apocalyptic flicks — from Soylent Green to An Inconvenient Truth — is anything to go by, Surviving Progress will be both critically acclaimed and seen by many. That raises an interesting question: Why are we as a species so willing to believe in doomsday scenarios that never quite materialize? In their new book, Abundance: The Future Is Better Than You Think, authors Peter H. Diamandis of the X‑Prize and journalist Steven Kotler offer one plausible explanation.

Human beings are constantly bombarded with information. Because our brains have a limited computing power, they have to separate what is important — such as a lion running toward us — from what is mundane. Because survival is more important than all other considerations, most information enters our brains through the amygdala — a part of the brain that is “responsible for primal emotions like rage, hate and fear.” Information relating to those primal emotions gets our attention first because the amygdala “is always looking for something to fear.” Our species has evolved to prioritize bad news. Pessimists survived, while optimists got eaten by lions.

Newspapers have long since realized that pessimism sells. According to one analysis, about 90 percent of all articles in The Washington Post tended to be pessimistic in tone during the period studied. As the old saying among journalists goes, “If it bleeds, it leads.” Politicians, too, have realized that banging on about “crises” increases their power and can, at least in Al Gore’s case, lead to a Nobel Peace Prize.

Surviving Progress will be watched because the brains of the mammals who went to the moon and discovered the secrets of the atom evolved by running away from wild animals. That does not detract from human accomplishment. If anything, it makes human progress even more amazing.