We're in the midst of the Earth’s sixth mass extinction crisis. Harvard biologist E. O. Wilson estimated that 30,000 species per year (or three species per hour) are being driven to extinction.

The global human population has been climbing for the past two centuries. But what is normal for all of us alive today — growing up while the world is growing rapidly — may be a blip in human history.

The population crashed following climate change about 930,000 years ago, scientists concluded. Other experts aren’t convinced by the analysis. By Carl Zimmer No place on the planet has escaped the ...