This was a terrible year, and also maybe the best one yet for humanity

As the year ends, civilians are dying at a staggering pace in the Gaza Strip and the genocide in Darfur may be resuming. A man charged with 91 felonies is leading in American presidential polls, and our carbon emissions risk cooking our planet.

But something else is also true: In some ways, 2023 may still have been the best year in the history of humanity.

How can that possibly be?

Just about the worst calamity that can befall a human is to lose a child, and historically, almost half of children worldwide died before they reached the age of 15. That share has declined steadily since the 19th century, and the United Nations Population Division projects that in 2023 a record low was reached in global child mortality, with just 3.6% of newborns dying by the age of 5.

That's the lowest such figure in human history. It still means that about 4.9 million...