Does social status shape height?

The Maya people of Guatemala are among the shortest people in the world. Men on average hover a few inches above 5 feet and women a few inches below. But if they move to the United States as children, the Maya grow taller. That extra growth carries to the next generation: Maya children born to Guatemalan immigrants in the United States are roughly four inches taller than their peers in Guatemala, research by biological anthropologist Barry Bogin shows. Some of that gap disappears as children reach adulthood, but even then, Maya people in the United States are still taller than people in their native country.

Economists have long observed increases in height across immigrant communities worldwide. Improved nutrition and sanitation are the conventional explanations for such growth.

But Bogin, of Loughborough University in England, and other researchers think there’s more to it than just better health. Even wealthy children in Guatemala tend to be shorter than children who grow up in the United States. Moving a child from one society to another — even if their lifestyle doesn’t change significantly — shifts their growth trajectory to match that of children in their new community, Bogin says.

His proposal that height has a social component rests on evidence that genetics and nutrition can’t explain all variation in human height (SN: 5/13/20). It’s also based on research in behavioral ecology showing that the growth of many social animals adapts in response to members of their community, a phenomenon referred to as “strategic growth.” In species with rigid hierarchies, dominant members often grow larger while subordinate members stay smaller.

Strategic growth also drives growth in humans, Bogin proposed in 2021 in Human Biology and Public Health. His research suggests that height not only reflects a person’s perceived social status within their community, but also their society’s underlying political and economic conditions. For instance, height disparities are wider in highly unequal societies and shrink in more egalitarian ones. When people in highly stratified countries move to more egalitarian communities, they tend to grow taller, studies of Western countries suggest. Based on animal research, Bogin suspects hormones, including those released when the body is under stress, may modulate the social aspects of height.

“It all sounds like … manifesting. You see other tall people and then also want to be taller and then you become taller.”

Gert Stulp, sociologist

Many researchers agree that the stress of living in a harsh environment can suppress growth. But they balk at the idea that one’s peers can influence height. “It all sounds like … manifesting,” says sociologist Gert Stulp of the University of Groningen in the Netherlands. “You see other tall people and then also want to be taller and then you become taller.”

But Bogin is a renowned height researcher. His book Patterns of Human Growth, now in its third edition, is among the most widely read textbooks in the field. That reputation has left colleagues inclined to consider what might otherwise sound outlandish.

It’s plausible that social status influences human growth, says behavioral ecologist Peter Buston of Boston University, who studies strategic growth in clown fish. But he urges caution. Bogin and his collaborators “haven’t yet done the studies that I would like to see done to make the strong case,” Buston says.

Framing height as at least partially socially driven could have profound implications for public health. Extreme shortness among children, or stunting, seen in some 149 million children under age 5 worldwide, might be a sign of social disadvantage rather than malnutrition, Bogin and others argue. What’s needed in such cases may not be nutrition supplementation, the common approach, but programs that alleviate societal inequities.

Social status, size and clown fish

The clown fish Buston studies live in colonies of two to six fish. The largest member is the breeding female followed by the breeding male. The remaining fish, none of whom breed, get progressively smaller, so that each is about 80 percent the size of the fish ahead of it in rank, Buston has found.

This rigid hierarchy helps prevent conflict, Buston theorized more than two decades ago. A graduate student in his lab recently found that if a larger fish is introduced into a colony to replace a smaller fish, the large fish gets shunned. A smaller replacement fish doesn’t.

In the wild, eviction, and the resulting exposure to predators, would be a likely death sentence. In clown fish at least, Buston says, “there’s been really strong natural selection for individuals who can regulate their growth and turn their growth on and off.”

Strategic growth also shows up in social mammals. Consider meerkats, which live in groups of three to 50 members with a dominant breeding pair that accounts for 90 percent of the group’s reproduction. Those two meerkats are also typically the largest. Smaller, often younger subordinates help feed and care for the pups, with the largest nondominant animals replacing the dominant breeding pair if they die.

In one experiment reported in 2016, researchers gave a nutritional supplement of hard-boiled eggs to some small, nonbreeding meerkats in a wild group, which helped the animals grow bigger. Meerkats that subsequently became dominant continued growing heavier in the two to four months after reaching the top rank, even when egg supplementation ended.

Hormonal changes associated with a rise in the social hierarchy may explain that continued growth, the researchers suspect. Dominant females have higher levels of the sex hormones estradiol and progesterone than subordinate females. And both dominant males and females have higher levels of cortisol, a primary stress hormone. Sex hormones and cortisol regulate growth in mammals (though high cortisol probably suppresses growth in humans).

Growing larger may come with trade-offs, the meerkat researchers think. Allocating extra resources to growth may well decrease disease-fighting ability or shorten life span.

Strategic growth may also occur in species with very different mating structures from clown fish and meerkats. For instance, among African riverine antelopes known as the puku, males fight for territory to attract females. A male with his own territory secretes more scent-marking hormones than males without one. The rise in hormones coincides with increases in the territorial male’s size.

Height is a puzzle

But what factors influence human height and by how much remains an open question. Genetics is no doubt involved, though it doesn’t seem to account for all patterns. Same for nutrition and sanitation. Evidence from the present and past hint that other factors must also be at play.

An analysis of 168,000 children in India and sub-Saharan Africa, for example, found that eldest sons in India were taller, on average, than eldest sons in Africa. But other Indian siblings were shorter than children of the same age and birth rank in Africa. The findings, reported in 2017, suggest that Indian children have the genetic potential to grow as tall as sub-Saharan African children, but for some reason only eldest sons attain that potential. The wealthiest families in India showed the widest height disparities between older and younger siblings, unexpected if nutrition or sanitation were the primary issues.

Archaeologist Samantha Cox of the University of Pennsylvania has found a similar height disparity among adult females in early Neolithic communities in Europe. Analyzing ancient DNA samples from skeletal remains that date back some 7,000 years, Cox discovered that females in North Central Europe (modern-day northern Germany) measured a couple inches shorter than females in South Central Europe (southern Germany, Austria and Slovakia), despite similarities in genetics and resource access. Males across both regions, meanwhile, were the same height, Cox’s team reported in the February Nature Human Behaviour.

Northerners, however, had considerably more physical signs of stress than southerners. Cox thinks that may be due to the challenges northern Neolithic communities faced in growing food. Some social factor may explain why northern males were able to recover from that stress while northern females were not. Females in the north may have suffered discrimination. “It seems pretty clear that there is male preference here,” she says.

These and other status-related differences in height have been observed in modern societies too. “High-social-status people are taller than low-status people…this is definitely true,” Stulp says. For instance, tall people tend to earn more money than short people, creating a so-called height premium.

That premium, though, varies by geography, researchers reported in 2023 in Economics & Human Biology. In wealthy, typically Western countries, such as the United States and Australia, the height premium is lower, on average, than in countries in Asia and Latin America. The researchers attribute this discrepancy to the role of environmental conditions, which become more variable as poverty rises. So compared with people in high-income countries, people in lower-income countries may more likely associate tallness with better health and fitness, resulting in a greater height premium.

Economists have known for decades that height variations, especially those related to class or gender, can provide clues about a society’s social order. “We know that height is very sensitive to inequality,” says Joan Costa-Font, a health economist at the London School of Economics and Political Science.

Inequality has been linked to shorter populations overall. Such disparities show up early in life and tend to persist into adulthood. In one analysis, researchers evaluated the heights of more than 37,000 children ages 4 to 6 from five affluent countries. Inequality, measured on a standardized scale, varied; the United States was the most unequal, followed by the United Kingdom, Australia, the Netherlands and Sweden. Children in the Netherlands and Sweden were taller at every income bracket than children from the other three countries, researchers reported in 2019 in BMJ Paediatrics Open. And the disparity from country to country was widest for children in the lowest income bracket.

Even in well-off countries, where starvation is not a concern, inequality may aggravate stressors known to worsen health, and potentially height, such as low social belonging and caregivers’ longer working hours, the researchers say. More egalitarian countries typically offer generous social programs that reduce such burdens.

Increasing social parity could explain why people in Western Europe have been growing taller for the last 140 years, says Björn Quanjer, a historical demographer at Radboud University in Nijmegen, Netherlands. But it can’t fully explain why some populations are taller than others. Men born in 1980 average about 6 feet in the Netherlands compared with 5 feet, 9 inches to 5 feet, 11 inches elsewhere in Europe.

“All Western European countries grew taller, but the Netherlands outgrew them,” Quanjer says. High education levels, low disease burden, good nutrition and genetics are all cited as possible explanations for that extra height. But, Quanjer says, “the simple answer is we don’t know.”

Do humans experience strategic growth?

Bogin and others, including pediatric endocrinologist Michael Hermanussen, theorize that strategic growth, as seen in clown fish and meerkats, might underpin at least some of what is going on.

Hermanussen has been identifying patterns in human height variations using European military records for decades. His research on conscript data on East and West Germans shows that before reunification began in 1989, East German conscripts were roughly one inch shorter than West German conscripts.

That height disparity made little sense to Hermanussen, who runs a private practice in Altenhof, Germany. East and West German boys were genetically similar. What’s more, both sets of boys were about the same height until age 12 or so, suggesting that nutrition wasn’t likely the major contributing factor either.

After reunification, the height of East German conscripts steadily increased. Within five years they were as tall as West German conscripts. Hermanussen suspected that the massive social and political changes that occurred after the fall of East Germany’s notoriously manipulative regime explained that collective growth spurt (SN: 5/16/23).

Others were skeptical, Hermanussen says. “People thought…it must be genes, it must be health, it must be nutrition.”

Hermanussen went on to work on another population with human biologist Christiane Scheffler of the University of Potsdam in Germany and statistician Christian Aßmann of the University of Bamberg in Germany. They found what Hermanussen and Scheffler now think is a sign of strategic growth in Swiss conscript data spanning three time frames: 1884–1891, 1908–1910 and 2004–2009. Looking at Switzerland as a single network with 169 cities linked via 345 roads, the team found that conscripts’ height tended to cluster in more connected communities. If one community was relatively short, then the neighboring community was likewise short.

“The community effect was quite clear,” Hermanussen says. “When you look at people who live in groups, they are almost all the same in height.”

What’s more, he found that increases in height in Switzerland over time varied from one district to another, but variation in height within a given community stayed the same. That is, everybody grew taller by roughly the same amount.

“It must be something in the air,” Hermanussen recalls thinking, until he came across the meerkat experiment. What if, Hermanussen wondered, Europe’s democratization, starting in places like Switzerland and the Netherlands in the mid-1800s, was akin to the equalizing in size of rival meerkats? As with the meerkats, such equalization could perhaps lead to a height race. Without a rigid hierarchy, people may continuously jockey for social position, Hermanussen supposes. “This makes people tall.”

In human societies, social scientists refer to this freedom to rise in rank as social mobility. Bogin suspects a lack of mobility in Guatemala keeps people short. Inequality is high, with some surveys suggesting that just a couple hundred people control roughly half the country’s wealth. Most Maya families live in poverty, with little opportunity for advancement. Even Maya and non-Maya families of means must contend with the constant threat of kidnappings for ransom and other violence.

People in Guatemala lack hope for a better future, Bogin argues. “Stress hormones block growth hormones.”

In the United States, a cleaner environment and better food certainly help immigrants grow, Bogin says. But so, too, may social factors, including living in a safer world and optimism about the future.

The relationship between stunting and status

If height does have a social component, then conventional public health wisdom tying stunting primarily to starvation may need a rethink. Starvation unquestionably inhibits growth, Scheffler says. But just because a person is short does not mean they are starving.

For instance, in a study reported in 2020 in the European Journal of Clinical Nutrition, Scheffler and colleagues recruited more than 1,700 children, ranging in age from 6 to 13, from three areas of Indonesia: West Timor, among the poorest regions in the country; North Sumatra, a more affluent, low-industry province; and Bali, a wealthy tourist enclave.

The researchers measured both the children’s height and skinfold thickness, or subcutaneous fat, at various spots on the body. Based on the skinfold thickness, none of the children who would’ve qualified as “stunted” showed signs of malnutrition. Zooming in on more than 700 children in West Timor, where stunting rates ranged from roughly 9 percent among youngsters from the wealthiest families to 47 percent among the poorest, the team again found no link between stunting and malnutrition.

Rather than a proxy for malnutrition, stunting is a proxy for social disadvantage, Scheffler argues. “It could be that malnourished people are stunted, but stunted people are not always malnourished.”

“We know that height is very sensitive to inequality.”

Joan Costa-Font, health economist

That could help explain a growing body of research showing that nutrition interventions do little to improve child growth, says anthropologist Emily Yates-Doerr of Oregon State University in Corvallis. “Global health professionals are finding it difficult to feed people taller.”

Precise numbers for how much money goes toward reducing stunting worldwide are hard to come by. One 2016 estimate suggests that globally, countries spend almost $4 billion per year to address stunting and other hunger-related issues, such as anemia. And many researchers and policy makers believe that substantially more money is needed. “Height is a signal and this needs to be discussed and to be understood. Because if we misinterpret the signal, we draw false conclusions,” Hermanussen says.

But not everyone is convinced that social status plays any role in human height, let alone a big role. Research suggests that humans can show dominance in ways besides height, such as by walking together in a group — displaying power in numbers — or using weapons, says Christopher von Rueden, an evolutionary anthropologist at the University of Richmond in Virginia. Gauging social status via height and not, say, collective fighting ability or muscle mass, he says is “odd.”

And human societies are complex. In particular, social networks are fluid, with people moving in and out. Any signal from strategic growth may be swamped by other factors.

Central to the debate is one’s view of human nature. Would a pecking order persist in human societies if other inequalities could be erased? Or would the need for a ranking system also go away? In the absence of the elaborate political and cultural systems thought to drive inequality among humans, social animals still establish hierarchies, Bogin says. Why should an equalized human society be any different?

“If everything were totally equal for everybody…we would still have a lot of variation in height,” Bogin says.

But many researchers studying height disagree. If resources were equally divided, height variations that Bogin and others attribute to social status would disappear too, says Cox, adding: “Height seems like such a basic trait. I think a lot of people would be really surprised to know how little we actually understand about it.”