Do you find it difficult to get away from it all? Your introverted ancestors had it a bit easier. Peace and quiet was, generally, more accessible before 1900. The twentieth century brought us the internet, smart phones, and hundreds of other technologies that keep us in contact but also make it difficult to get away. There’s also another key reason why it’s difficult to get alone time in today’s world: More people.

The human population quadrupled over the course of the twentieth century, from about 1.6 billion people in 1900 to just over 6.1 billion in 2000. The largest population increases happened in Asia, where countries like India and China led growth, expanding from about 950 million to 3.7 billion people. The fastest growth by percentage, however, took place in Africa, which grew from 133 million to 800 million. Despite two devastating world wars that together killed almost 100 million people, in almost every nation on Earth, populations were higher at the end of the twentieth century. In the twenty-first century, populations have continued to rise: In November 2022, the Earth’s total population reached 8 billion.

Why did our population grow so rapidly? There are lots of reasons, including an overall decline in warfare (surprise!) and better nutrition. But the most important cause of population growth in the last 125 years has been a dramatic drop in child mortality. According to the United Nations and the World Bank, in 1900, one in three children died before age five; today, it’s fewer than one in twenty. And it’s not just child mortality that’s dropped—once we’ve survived the dangers of childhood, medical and scientific innovations have helped us defeat and recover from diseases better, and live longer.

It seems like a simple story, and a good one—at least for everyone except the most extreme introverts. Unfortunately, the reality of the twentieth-century battle to improve health is more complex. In this article, we’re going to embrace that complexity and find out about both the victories of the fight for better human health and its limits. This information is important for understanding the past, but it’s also an important tool for thinking about the future . Today, our relationship to our health is getting both better and worse at the same time.

Amazing innovations

There is plenty of evidence to support the argument that medical advances in the twentieth and early twenty-first centuries have been incredibly beneficial for humans. We can recite a long list of innovations that reduced death rates from disease and increased both the quality and length of human lives overall.

One of the most obvious beneficial health technologies was the invention of antibiotics. In the late nineteenth century, scientists were able to show that tiny microorganisms caused many diseases. They called this idea the germ theory of disease. Research in London showed that cholera was caused by bacteria living in water. French researchers showed that food poisoning happened when microbes infected our food and drink. And German researchers found that bacteria moving through the air caused tuberculosis. Despite these discoveries about the causes of disease, the diseases themselves remained untreatable. Then, in 1928, Alexander Fleming discovered penicillin, the first true antibiotic. By the 1940s, penicillin was being mass-produced to treat wounded soldiers in World War II. Penicillin and the antibiotics that followed made it possible to treat deadly bacterial infections like pneumonia, tuberculosis, and strep throat. They drastically reduced deaths that were once very common, especially in young children. As antibiotics became widely available, more and more people survived illnesses that once were fatal.

Vaccines also played a key role in preventing disease and saving lives, especially after World War II. Over the twentieth century, vaccines for measles, diphtheria, and other diseases were developed and distributed, helping to reduce global child mortality. In the 1950s, the polio vaccine was introduced to protect children from a disease that had once caused paralysis and death. One of the most important achievements of the twentieth century was the eradication of smallpox in 1980, which followed a global vaccination campaign led by the World Health Organization. Vaccines had a huge positive impact. In 1950, more than 20% of children died before their fifth birthday; by 2000, that number had dropped below 10%.

Other medicines and even medical machines were also very important. Oral rehydration therapy (ORT), developed in the 1960s, became a simple but lifesaving solution for children with diarrhea, especially in low-income countries. Meanwhile, the discovery of insulin in 1921 helped people with diabetes survive a disease that was previously fatal. New medical imaging technologies like X-rays (first used in 1895), CT scans (1970s), and MRIs (1980s) helped doctors diagnose diseases more accurately and treat them earlier.

Other public health innovations improved infrastructure and the organization of our health and sanitation systems.. Over the twentieth century, cities developed clean-water systems, sewage treatment, and waste disposal networks, helping reduce diseases like cholera and typhoid. These advances were particularly effective in places that had modern public health systems, supported by governments, hospitals, businesses, and international organizations.

Inequalities in health and medicine

Even though humanity has made huge advances in the science of medicine, disease control was not equal during the twentieth century, and it remains unequal today. Environmental problems and the legacy of colonialism have made it harder to fight disease in some parts of the world, especially in the global south (Africa, Latin America, and parts of Asia) and among poor communities in wealthy countries.

For example, malaria, a disease spread by mosquitoes, was almost totally eradicated from Europe in the twentieth century, but it still kills hundreds of thousands of people every year in sub-Saharan Africa. This disparity has a lot to do with the history of colonialism during this century. Countries that were once colonized tend to have weaker health systems and thus less money to spend on mosquito control or medicine. These differences continue to be a problem today. Another good example is the repeated Ebola virus outbreaks in Central and West Africa over the past 30 years. Thousands died because hospitals were underfunded while years of colonialism and war had weakened public trust in government and international health workers. Some people in this region refused treatment because they feared outsiders or didn't understand what was happening—partly because of a long history of being mistreated by corporations and colonizers from industrialized countries.

Even in wealthy countries like the United States, poor communities suffer more from disease than their wealthier neighbors. Poor people in the United States, and particularly poor people of color, are much more likely to have asthma than the wealthy. This is because they’re more likely to live in neighborhoods near polluters like highways and factories, where housing is cheaper. Poor communities are less likely to have access to quality healthcare facilities, are less likely to have health insurance, and generally receive less education about health matters. They’re also more likely to be exposed to mold and pests (both of which carry health risks) in their housing.

In short, medical breakthroughs are powerful, but they’re not enough. History, inequality, and the environment still play a big role in global health.

Modernity also leads to disease

Modern science and technology have helped people live longer, but there is evidence to suggest they have also created new health problems. As the world has become more industrialized, urbanized, and globalized, new diseases have emerged, and some older diseases have become harder to control. These changes show that even progress can have unintended health consequences.

The rising human population partly explains the emergence of these new diseases. When people live in large, crowded cities and have access to international air travel, it becomes easier for diseases to spread quickly. In places with poor sanitation or limited healthcare, this can lead to outbreaks of infectious disease. This dynamic probably contributed to the development of COVID-19, for example. At the same time, as farms and towns are built in formerly wild areas, humans come into closer contact with wild animals that carry viruses, thereby introducing new diseases into human populations. Scientists believe that HIV came from chimpanzees in Central Africa, and some coronaviruses may have come from wild animals that humans hunted or disturbed.

Modern life has also led to a rise in noncommunicable diseases, especially in wealthier countries. Many people in these societies live sedentary lifestyles, eating processed foods that are high in sugar, fat, and salt. This has caused a rise in obesity, type 2 diabetes, and heart disease. Even children are being diagnosed with these illnesses.

At the same time, the toxic mix of chemicals we use in our industrial societies can be bad for our bodies. For example, plastics, radiation, and pollution probably all contribute to rising rates of cancer. Many everyday products—like packaging, cleaning supplies, and cosmetics—contain chemicals that may interfere with hormones or damage cells over time. In some cities, air pollution from factories and cars has been linked to higher risk of lung cancer and asthma, especially for people who live in low-income neighborhoods. Radiation exposure, whether from nuclear accidents or overuse of medical imaging, can also increase cancer risk. Scientists are still studying the long-term effects of microplastics, which have been found in human blood and organs.

Climate change is another big factor leading to increases in some diseases. As temperatures rise and rainfall patterns change, mosquitoes and ticks that carry diseases like dengue fever and Lyme disease are spreading to new areas that were once too cold for them. Floods and hurricanes contaminate drinking water, leading to incidents of diseases like cholera, even in wealthy nations. And excessive heat can itself kill people, particularly in poorer nations and communities where air conditioning is unavailable.

Even the fact that we are living longer means that we must face new diseases. For example, many people today live long enough to develop Alzheimer’s disease, which was rare in the past. More elderly people also means more cases of arthritis, heart disease, and cancer, which increase with age.

Medicine is not enough

Even though modern medicine has saved millions of lives, it has never been enough on its own to stop disease. Environmental problems, poverty, and political conflict often make it harder for people to get the care they need.

Here’s an example: Even though the cause of cholera was determined in the 1850s, outbreaks still happen today. They don’t happen in London, where the microorganism that causes cholera was first determined. Rather, outbreaks happen in places where people don’t have access to clean water or proper sewage systems. In 2010, after a major earthquake in Haiti, cholera spread quickly because the water supply was contaminated. Because the country lacks a strong public-health infrastructure, cholera still affects some Haitians today.

Another example is tuberculosis (TB), a disease that can be cured with antibiotics. TB continues to spread in poor or overcrowded areas, especially in parts of South Asia and Eastern Europe. And in the United States, some diseases are returning because people are hesitant to take the vaccines that can protect against them—even vaccines that have worked for almost half a century.

These examples show that fighting disease requires more than medicine—it also requires improving living conditions, ending poverty, and building trust in public-health systems.

What’s the lesson?

Despite all the limitations, it’s still probably fair to applaud the successes in the fight against disease in the twentieth century. More children survive to adulthood than ever before. Diseases that once terrorized our ancestors—such as smallpox—have been reduced or eliminated. These are accomplishments worthy of celebration. And there’s good reason to believe that scientific research can help us to solve even more human health problems in the future.

Still, many challenges remain. Poverty and inequality continue to mean that some people don’t get the help they need. Worsening pollution, climate change, and other modern conditions cause new diseases to emerge and spread. To make matters worse, there is a growing distrust of the science and scientists that create new technologies and produce innovations in medical treatments. To overcome some of these challenges, we can learn from the successes and failures of the past, as we hope to do better in the future.