A few years ago, I attended a dinner party where a friend of the host launched into an exhaustive diatribe about the problem with “breeders.” In his view, couples with children are selfish, narcissistic, and irresponsible, contributing to overpopulation. What he didn’t know at the time was that I was expecting.

I’ve heard this opinion many times before. Several friends and academic colleagues vocally opt not to have kids in order to “save the planet.” To them, population numbers are a simple input and output equation in which more people create more problems. Thankfully, it takes more than math to understand the mechanisms that shift the balance of life on Earth.

Here’s the part that’s not up for debate: Some of the greatest challenges we face globally stem from our current predicament. Too many people are squandering ever more limited resources including food, water, energy, and more. Climate change exacerbates these problems.

Our numbers are on the rise. When I was born in 1980, the global population was approximately 4.5 billion people. Around 2050, we’ll have doubled that to nine billion. The world is getting increasingly crowded, but a bustling planet is not necessarily doomed. What matters most is how those billions of people choose to live.

Scientific models warning us about unchecked population growth have been around for hundreds of years, most notably from the reverend Thomas Malthus in the late 18th century who concluded that “the power of population is indefinitely greater than the power in the earth to produce subsistence for man.”

More recently, a work that sparked ethical questions over whether couples ought to have children came in 1968 from Stanford professor Paul Ehrlich. His book, The Population Bomb, sounded an alarm that there would not be enough food to support humanity over coming decades. He predicted famines in the 1970s would kill hundreds of millions of people and only stringent birth control measures could be the solution. When The Population Bomb became a bestseller, overpopulation was dubbed the leading environmental crisis of our time and couples at home and abroad began to reconsider whether they would have children at all.

These dire predictions didn’t come to pass. Five decades after The Population Bomb’s publication, average calories consumed per person have risen in populous countries such as India and China. The Green Revolution made it possible to grow more food so that where and when famines do occur today, they are largely the result of distributional shortcomings rather than an inadequate food supply.

Since the 1960s, global fertility rates—the number of live births per woman—have decreased dramatically, with no stringent birth control measures required. Scientists now predict that the human population will peak within this century, somewhere around 10 billion, before declining for the first time in modern history.  

I’m not going to suggest that the errors in previous population models were entirely due to being created by men, but we now know that those responsible (mostly) men didn’t anticipate the way women would opt to have fewer children when their circumstances changed.

During the last half-century, in both developed and developing nations, more women were educated, joined the labor force, and had access to birth control, making better family planning possible. Meanwhile, scientific innovations like antibiotics and vaccinations kept families healthier. As a result, women all over the world chose to have fewer children. The global fertility rate has fallen from close to five live births per woman in the 1960s to about 2.5 births today and will continue to decrease in the future. It remains high in places like sub-Saharan Africa and Southeast Asia where child mortality is high and health conditions are poor.

Still, Ehrlich and his predecessors were not entirely wrong. We do face many real challenges, but not every person has the same impact on Earth. The real danger isn’t in sheer number of humans, but how specific individuals and societies use resources.

Consider global energy consumption, which is directly related to food, water, and climate change: On a per capita basis, the average Texan consumes about twice as much energy as the average American, four times as much energy as the average person in the United Kingdom, and eight times as much energy as the average person in China.

We were spared the famines of the 1970s, but one billion people around the world currently suffer from chronic hunger because the food we have doesn’t reach all of us. The bounty we have now thanks to the Green Revolution will only take us so far. According to the Bill and Melinda Gates Foundation, agricultural yield will need to increase by 70 to 100 percent in order to meet the global food demand anticipated by 2050 when we reach 9 billion people. [

One way to have an immediate impact would be to simply limit the food we waste, which accounts for nearly half of what we grow in the United States. That adds up to about 1,400 calories per person per day, or 31 million tons of food per year that’s grown but never gets eaten. An enormous amount of energy is involved in planting, fertilizing, harvesting, packaging, shipping, storing, refrigerating, and preparing food that goes unconsumed. Wasted food is wasted energy. Conservative estimates out of the University of Texas at Austin suggest that wasted food accounts for at least two percent of the entire U.S. energy budget every year.

Along with that food and energy, we also lose a lot of water as Earth gets hotter and drier. Climate change doesn’t just make warm termpertures warmer, but wet regions wetter, storms deadlier, and droughts more severe. Scientists know that the water shortages we are experiencing in 2014 will get worse.  Taking short showers and opting not to water your lawn has some influence on the water budget, but what most of us don’t realize is that the vast majority of water we do have goes toward agriculture through food, fuel, and fiber production. In the U.S. alone, agriculture accounts for 80 percent of our total water consumption. Unfortunately, much of that gets lost through to old leaky water technologies as well as simple oversight. Biologists and engineers are working to develop more drought tolerant crops that will require less water to grow. We can also boost federal investment in water treatment and infrastructure.

The answers to these limited resource challenges will be found through research and innovation. Yet if national priorities can be illustrated by where we spend tax money, the U.S. has not focused on finding solutions. The portion of our federal budget going toward research and development has decreased over the last 50 years. At the peak of the space race in the late 1960s, research and development accounted for nearly 12 percent of the total U.S. budget. Today we spend just over three percent on research and development.

Despite these figures, there’s data to suggest we can be optimistic about the future—and parents are part of the reason why. In my role at the University of Texas at Austin, I survey national attitudes related to energy and the environment. Over the past few years, I started to notice that people with children tend to be more concerned about the environment than the general population and more interested in changing their behavior to be smarter consumers. For example, parents are consistently more likely to acknowledge that climate change is occurring. They also express more interest in purchasing energy efficient cars and installing solar panels. It sounds intuitive that parents feel they have a bigger stake in the future and want the best for their families, but now we have data demonstrating it’s true.

So when affluent couples in developed nations opt not to have kids “for the good of the planet,” they may have good intentions, but their decision does not get at the core problems underlying the global challenges of overpopulation. In fact, the data suggests they may be less invested in Earth’s state over the long-term.

Families are already getting smaller all around the world. If we figure out how to live more efficiently with less waste, while supporting women and families, we will achieve a healthier and more sustainable future. So even as the planet gets hotter and ever-more-crowded, it’s still okay to have kids.