If you were born at the beginning of the 20th century, you could expect to live about 31 years based on global averages. Today, around the world, the average human life span is more than 67 years, and in developed nations it’s more than 80. A big reason for the extension of average life spans is the improvement in the health of children. In 1900, 10 percent of babies born in the United States died before their first birthdays. Our current infant mortality rate is less than 1 percent.

In 1820, 85 percent of human beings were desperately poor, living on the equivalent of less than $1 a day. Today, just 20 percent of us live in those dire straits, and that number continues to fall. Some experts think we will have completely eliminated that level of extreme poverty by the beginning of the next century.

Author Steven Pinker compellingly describes how violence has diminished across human history in his new book, The Better Angels of Our Nature: Why Violence Has Declined. He offers a battery of statistics. Murder rates have declined steeply. England in the 1200s recorded 24 homicides per 100,000 people. Now it’s less than 1 per 100,000. More recently, battle deaths in international conflicts have declined from 65,000 per year around 1950 to fewer than 2,000 per year in the present decade. Nearly every imaginable index of cruelty and violence has declined across time. We’re kinder to animals (gambling on dogfights, cockfights and bull-baiting used to be hugely popular); kinder to people of different races and ethnicities; generally opposed to slavery; and, by and large, we don’t let people beat their wives or children, which is a comparatively new standard.

As Pinker says, “Whatever its causes, the decline of violence has profound implications. It is not a license for complacency: We enjoy the peace we find today because people in past generations were appalled by the violence in their time and worked to end it, and so we should work to end the appalling violence in our time.”

Furthermore, we should study what we’ve accomplished to see whether we can get better at it. “Man’s inhumanity to man has long been a subject for moralization,” Pinker says. “With the knowledge that something has driven it dramatically down, we can also treat it as a matter of cause and effect. Instead of asking, ‘Why is there war?’ we might ask, ‘Why is there peace?’ ... We must have been doing something right. And it would be nice to know what, exactly, it is.”

Still, looking at what we’ve achieved, it doesn’t seem unreasonable to think we can solve present and future challenges. We can live on this planet in a sustainable way. We can preserve its health and vitality for future generations. And we can make the lives of future human beings even better than the lives we lead today — we have a track record for that kind of achievement.