This article was originally published in USA Today.

For much of our history, most humans lived far more perilous lives than we live today. Our challenge is less about our material conditions and more about our mindset.

Declining birth rates are a major concern for the United States and many countries around the world, so we – an expert in existential psychology and an expert in pulsing public opinion – surveyed the Americans choosing not to have children to learn the reasons why.

Americans are having fewer children than are needed to keep population numbers stable.

Low birth rates are not only an American problem. In 2020, researchers at the University of Washington’s Institute for Health Metrics and Evaluation projected that the global fertility rate will drop below 1.7 by the end of this century. And countries such as Italy, South Korea, Spain and Thailand will lose more than half their population within the lifetimes of children being born this year.