By comparing “first wave” developing countries, like Sweden and the United States, to “second wave” developers, like South Korea and Japan, Thomas Anderson and Hans-Peter Kohler of the University of Pennsylvania seek to explain why countries that underwent socioeconomic development in the first half of the 20th century have slightly higher fertility levels than those that developed later. Despite “both sets of countries attaining high income and generally low fertility, contemporary gender norms and levels of gender equity differ between them,” write Anderson and Kohler in a new study in Population and Development Review.

According to recent polling, climate change is seen as the single most threatening international challenge around the world, and there’s evidence that all that worry is taking a psychological toll. Adding to droughts, floods, extreme weather, and die-offs, psychologists are observing higher levels of anxiety, depression, and post-traumatic stress disorder in certain areas and professions. Even people who do not actively stress about global warming or view it as a major threat may still suffer psychological trauma from its effects.

In most parts of the world, population growth is stagnant, even declining slightly, part of a decades-long and nearly universal shift towards smaller, healthier families. But the places where growth is still rapid continue to defy expectations about when they will “catch up.”

In 1968, Stanford University biologist Paul Ehrlich predicted hundreds of millions would starve to death over the next decade, many of them Americans, and the world would generally decline into chaos in his book The Population Bomb.

If you were on a mission to improve the plight of humankind, no less, would you care about how many people are living, where they are, and how old they are? You probably would, for it would obviously make it easier for you to estimate the challenge you face. However, the international community did not.

Hans Rosling has always been an innovator when it comes to bringing big ideas to big audiences. The Norwegian doctor, statistician, and co-founder of the Gapminder Foundation has become known – to the kind of people who watch TED Talks anyway – for lively presentations aimed at demystifying common ideas about global development and demography. On Gapminder.org, he literally stands chest-high in water appealing for your donation to help him “cross the river of myths.”