Facts So Romantic

The Case for Making Humans Smaller

When Arne Hendriks, a 6” 4’ Dutchman, faced audience members at TEDxBrainport in 2012, he smiled apologetically. “I have some bad news for you,” he said. “You’re not short enough.” Hendriks believes that the planet’s growing population—currently at 7 billion—is unsustainable. His solution? We should shrink ourselves to 50 cm, around the height of a chicken. “I think we can actually achieve that,” he says.

Scott MacBride/Getty Images

Hendriks, an exhibition maker and historian, chose the 50 cm figure for several reasons: It’s rounded down from the shortest adult ever recorded, the 57-cm tall Gul Mohammed from New Delhi; it’s the average height of a newborn baby, a stature that’s “not hard to imagine”; and at 50 cm, humans would consume 2 percent of the food and fuel we do now, according to Hendriks’ calculations, instantly ending most of the problems of overpopulation, from CO2 pollution, to water shortages, to skyrocketing rent.

Hendriks’ idea doesn’t seem too realistic, but its appeal is clear enough: With a tweak to our biology, miniature humans of the future could indulge our consumerist ways unfettered, freed from environmental concerns about habitat and resource depletion—at least to a point. (If our population reaches 350 billion, 50 times its current amount, that will bring us back to 100 percent of current consumption.)

But is our height in fact arbitrary and flexible?

For the last 2 million years, the height of mammals belonging to the genus Homo has risen gradually, with several sharp upticks. Around 500,000 BCE, as our ancestors evolved from tree climbers to ground walkers, body size increased dramatically, enabling us to cover more ground and forage plants and elude predators more effectively.

But then, about 50,000 years ago, humans started to shrink, according to Christopher Ruff, a professor of functional anatomy at Johns Hopkins University. This is likely due to improvements in technology, like spears, he says, which diminished our need to outwrestle large cats. Our smaller and more nutrient-efficient (and therefore more famine-resistant) ancestors passed their genes onto subsequent generations.

Over the last century, our species has seen an unprecedented species-wide growth spurt—a 4-inch increase on average. The most extreme examples are in Japan, where mean height has increased 5.5 inches in the last 50 years, and in the Netherlands, where people have grown eight inches in the last 150 years. This recent uptick differs from all other height fluctuations in history: It is due, not to natural selection, but to unnatural nutritional overabundance, writes Michael J. Dougherty, now director of education at the American Society of Human Genetics.

Better nutrition brings about manifold improvements to physical functioning, like sharper eyesight, stronger bones, and lowered risk for Alzheimer’s and heart disease. But an increase in height, though correlated with these improvements, is not itself one of them. In fact, while it is thought of as a “a composite code for all the factors that make up a society’s well-being,” as the New Yorker’s Burkhard Bilger writes, height itself may diminish the benefits with which it’s correlated.

Being bigger is no longer better.

Tall people have lower life expectancies, on average, than short people: They’re at increased risk for Alzheimer’s, heart disease, diabetes, and cancer—the latter because higher levels of growth hormone increases cell division rates and thus the likelihood for genetic mistakes. Though it was good for our ancestors to be large—outrunning predators and conserving thermal energy in cold winters was crucial for survival in their day—growing in the presence of good nutrition may be a vestigial response, given that those threats no longer persist. Being bigger, in other words, is no longer better.

But one might argue that the large size of the human brain is a necessary condition for our high intelligence levels—so if we shrink ourselves down, we’ll dumb ourselves down, too. This is true in a sense, says Dean Falk, an evolutionary paleoanthropologist at the School for Advanced Research, in Sante Fe, New Mexico. If we rewound the evolutionary tape, we’d find that primate intelligence decreases with primate size. But Falk says a reduction in brain size doesn’t necessitate a corresponding decrease in intelligence. Over the last 20,000 years, internal restructuring and rewiring has already made our brains smaller without any apparent negative side effects. What’s more, shrinking wouldn’t be an unprecedented occurrence in our evolutionary history: Homo floresiensis, or “the hobbit species,” appears to have shrunk from Homo erectus, says evolutionary anthropologist Karin Isler, as a result of living in the limited-food environment of the Indonesian island of Flores. Despite brain volumes of 380 cm3, roughly the size of a chimpanzee’s, Homo floresiensis’ cognitive capabilities were comparable to Neanderthals, whose brain volume—at around 1200-1600 cm3—equaled or surpassed our own.

Smaller brains may even have advantages. Brian Hare, an evolutionary anthropologist at Duke University, suggests that smaller brains tend be more social and have more of the traits we consider civilized. “Even though a wolf has a much larger brain than dogs, dogs are far more sophisticated, intelligent, and flexible,” he says.

Still, Hendriks’ campaign for 50 cm is potentially dangerous, says Matthew Liao, a bioethicist at NYU. “If you were that small,” he says, “you’d be eaten by cats!” Like Hendriks, Liao does argue that, “in light of the problem of climate change,” humanity should consider shrinking, just not as much. In his paper “Human Engineering and Climate Change,” he suggests we reduce our height by a more reasonable 15 cm, or 5 inches, which would merely reverse height’s artificial inflation in the last century. Liao has calculated that reducing the average US height by just 8 percent (15 cm) would mean a corresponding mass reduction of 23 percent for men and 25 percent for women, and a 15-18 percent reduction of metabolic rate. The effect of this downscaling “is not linear,” he says. “It’s exponential.”

Liao would accomplish this height reduction through pre-implantation diagnosis, a screening test used to determine whether genetic or chromosomal disorders are present in developing embryos before they are inserted into mothers through in vitro procedures. While height would be somewhat trickier to test than most hereditary diseases—it is controlled by 697 genetic variants, in contrast to the single variant of a hereditary disease like cystic fibrosis—Liao views this as a mere “technical problem.”

Once science works out the kinks, he says, parents could screen for tallness just like they do now for disease. 

Susie Neilson is an editorial intern at Nautilus.

The Case for Making Humans Smaller

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