Last century, there was a rapid human population growth.
The world's population could even decrease.
Texas State demographer and UTSA professor Lloyd Potter said fertility is down—below replacement levels for many populations, but that's not necessarily a bad thing.
"There's only so many resources on the earth, then the earth probably doesn't have the ability to sustain continued growth and consumption by an ever increasing human population," said Potter.
He said the human population of the world might become more imbalanced in terms of what the earth can generate for food and clean water.
Potter added population growth is in indicator of economic vitality, which makes some people get concerned when humans stop reproducing.
"Historically, throughout human history, we've been kind of focused on insuring our populations are healthy and continue to grow," said Potter.
He said there's significant fertility declines in many countries, like Africa, where fertility is usually high.