From candles to electrons: changing lighting sources in the United Kingdom

In 1961, around two chickens were slaughtered per person globally each year. As many countries grew richer — and richer countries tend to eat more meat — global demand for chicken increased.

Since then, the number of chickens slaughtered per person has quadrupled. On average, 9 chickens are killed each year for every person in the world. Chickens have also become much heavier, so the amount of meat eaten in kilograms has grown even faster.

Life is short and painful for many farmed animals. Global estimates suggest that most are raised in factory farms. In the United States, around 99% of livestock comes from them.

One of the starkest expressions of global inequality is a child’s chance of survival. In 2023, 2.84 million children in Africa died before reaching their fifth birthday, giving the continent the highest child mortality rate of any region (5.9%).

The chart above shows a simple hypothesis: how many more African children would reach the age of five if it had the same child mortality rates as other regions?

If conditions in Africa improved enough to match Asia’s current child mortality rate (2%), 1.9 million of these 2.84 million children would survive.

If the child mortality rate were to drop to the European rate (0.4%), then 2.64 million children would be saved each year.

Almost 20,000 Americans were murdered in 2023.

The chart shows the homicide rates among male and female victims. Men were 2.7 times more likely to die by homicide than women.

We can see that for men, most of these murders were committed by friends, neighbors, acquaintances, or strangers (shown as “Other” in the chart) rather than a partner or family member. The opposite is true for women: intimate partners are the biggest threat.

Because the risks are different, the most effective responses may differ too. For women, reducing intimate partner violence is a key priority. For men, prevention is more often tied to crime, gangs, and violence among acquaintances or strangers.

The 1970s were a decade shaped by fears about overpopulation. As the world’s most populous country, China was never far from the debate. In 1979, China designed its one-child policy, which was rolled out nationally from 1980 to curb population growth by limiting couples to having just one child.

By this point, China’s fertility rate — the number of children per woman — had already fallen quickly in the early 1970s, as you can see in the chart.

While China’s one-child policy restricted many families, there were exceptions to the rule. Enforcement differed widely by province and between urban and rural areas. Many couples were allowed to have another baby if their first was a girl. Other couples paid a fine for having more than one. As a result, fertility rates never dropped close to one.

In the last few years, despite the end of the one-child policy in 2016 and the government encouraging larger families, fertility rates have dropped to one. The fall in fertility today is driven less by policy and more by social and economic changes.

This chart shows the total fertility rate, which is also affected by women delaying when they have children. Cohort fertility tells us how many children the average woman will actually have over her lifetime. In China, this cohort figure is likely higher than one, but still low enough that the population will continue to shrink.

Seasonal influenza is sometimes seen as a mild illness, but it remains a major cause of death. In serious cases, it can cause deadly complications such as pneumonia, strokes, and heart attacks. Researchers estimate that the flu causes about 400,000 respiratory deaths and 300,000 cardiovascular deaths globally each year.

The flu is most dangerous for infants and older adults. The map here shows rates of respiratory deaths caused by the flu in adults aged 65 and over, averaged across 2002–2011 (excluding the 2009 Swine Flu pandemic).

The data shows that death rates tend to be higher in South America, Africa, and South Asia than in Europe or North America.

I come from South America, and I found this surprising: most of what I hear about flu deaths tends to come from richer countries in the Northern Hemisphere. But the map shows that the flu is also deadly, in some cases even more so, in other regions where poverty, worse underlying health, limited access to healthcare, and lower vaccination coverage contribute to higher mortality.

One explanation for my misperception might be that surveillance and reporting are stronger in the countries that I associate with deaths from flu. Another could also be age differences: people in high-income countries tend to be older, so their total number of deaths — the ones you actually hear about — may still be higher, even if rates are lower.

When you consider the total death toll, you realize that the numbers are very large on the whole. Recall that the map only includes respiratory deaths, so the overall mortality is actually higher if we include other flu-related complications like cardiovascular disease.

Even if you account for the uncertainty of estimates in low-income countries — due to limited testing and death registration — the overall pattern remains striking: seasonal influenza kills hundreds of thousands each year, with many of these deaths in South America, Africa, and South Asia.

Measuring happiness is difficult, but one way to understand how satisfied people are with their lives is to simply ask them.

Self-reported life satisfaction is one key metric that researchers often rely on. It asks people to imagine a hypothetical ladder, where the best possible life for them is a 10, and the worst possible life is a 0. They then have to place their current position on the ladder.

The chart shows the three-year average scores from 2022 to 2024 for the four countries with the highest ratings and the four with the lowest.

Afghans reported the lowest life satisfaction in the world, far below any other country.

This incredibly low score has been replicated in other studies. Researchers recently compared Afghans’ life satisfaction with international datasets dating back to 1946 and found it was the lowest ever recorded. Two-thirds gave a score of 0 or 1 on the 10-point scale.

Women are much more likely than men to be killed by their intimate partner. The chart shows this across nine OECD countries in 2023.

These deaths are rarely isolated events. Research shows that partner homicides are usually the endpoint of a long pattern of coercive control — behaviors such as surveillance, isolation, intimidation, restrictions on daily life, and physical violence.

Recognizing both the gender imbalance and its roots in coercive control can help focus support services, encourage family and friends to act sooner, and increase social pressure against abusive behavior.

While women face the highest risk from intimate partners, men make up about 80% of homicide victims globally. The gender split in partner homicides is therefore a striking exception.