News

May 06, 2023

Why human societies still use arms, feet, and other body parts to measure things

If you had to estimate the dimensions of a room without the benefit of a tape

If you had to estimate the dimensions of a room without the benefit of a tape measure, you might walk its perimeter heel to toe, counting your steps. To estimate the height of a wall, you might count hand spans from floor to ceiling. In doing so, you’d join a long human tradition. Most human societies around the word—perhaps all—have employed similar body-based measurement strategies, according to a first-of-its-kind study published today in Science. And these informal body-based systems can persist for centuries after a culture has introduced standardized units of measure because, the authors argue, they often lead to more ergonomic designs of tools, clothing, and other personalized items.

"Nobody has ever done this kind of systematic, cross-cultural study of body-based measurement before," says Stephen Chrisomalis, an anthropologist of mathematics at Wayne State University who penned an editorial accompanying the new paper. "It brings together a huge amount of data that [show] not just how common they are, but that they tend to fall along certain patterns. That is actually an extraordinarily important finding."

Many past and present standard units of measure have been inspired by human body parts. As early as 2700 B.C.E., the ancient Egyptians employed the royal cubit, a unit of length of about 53 centimeters that was likely derived from the distance from one's elbow to the tip of the middle finger. Other units still in use today, such as the foot and the fathom (originally the span of one's outstretched arms, now standardized to 1.8 meters) were similarly inspired.

Although standardized units are often upheld as superior to informal corporeal measures, people in many societies have continued to use their bodies this way well after standardization has taken root, notes Roope Kaaronen, a cognitive scientist who studies cultural evolution at the University of Helsinki.

To explore how widespread such practices have been in human history, Kaaronen and colleagues pored over ethnographic data from 186 past and present cultures across the world, looking for descriptions of body-based units of measurement in a database called the Human Relations Area Files. This database is the product of an international nonprofit organization that has been collecting and administering ethnographies and anthropological literature since the 1950s.

The team found these systems used in every culture they looked at, particularly in the construction of clothes and technologies. For example, in the early 1900s, the Karelian people, a group indigenous to Northern Europe, traditionally designed skis to be a fathom plus six hand spans long. In the late 1800s the Yup’ik people from the Alaskan coast recorded building kayaks that were 2.5 fathoms long plus a cockpit, which was the length of an arm with a closed fist.

Next, the team looked at a subsample of 99 cultures that, according to a widely used benchmark in anthropology, developed relatively independently of one another. Fathoms, hand spans, and cubits were the most common body-based measurements, each popping up in about 40% of these cultures. Different societies likely developed and incorporated such units because they were especially convenient for tackling important everyday tasks, the authors argue, such as measuring clothes, designing tools and weapons, and building boats and structures. "Think of how you’d measure a rope or a fishing net or a long piece of cloth," Kaaronen says. "If you measured it with a yardstick, it would be quite cumbersome. But measuring slack items with the fathom is very convenient: Just repeatedly extend your arms and let the rope pass through your hands. So it's no coincidence that we find the fathom being used for measuring ropes, fishing nets, and cloth around the world."

Body-based units also often result in more ergonomic designs, he notes, because items are made for the person actually using or wearing them. Kaaronen is a kayaker and woodworker who makes his own paddles—basing their length on a traditional measurement of his fathom plus his cubit. "I personally vouch for traditional paddle designs," he says. "They are very ergonomic and functional."

Advantages like these could explain why body-based measurements have persisted for so long, the team says. It found that these methods were still being used hundreds or even thousands of years after the introduction of standardized units in every region they examined.

Because the archaeological record rarely preserved these kinds of informal systems, and because anthropologists and ethnographers haven't always documented the use or absence of such measurement systems, it's impossible to say exactly how commonplace body-based units have been throughout history, Kaaronen stresses. "I’ve yet to encounter a culture where we could explicitly say that they haven't used any kind of body-based units of measure, though," he says.

Dor Abrahamson, a cognitive scientist at the University of California, Berkeley, calls the paper's analysis and conclusions "compelling." It serves, he adds, as a sort of counterargument to the push to standardize tools and objects for more convenient manufacturing. "I am a cellist, and there is this idea of a ‘lady's cello’—an instrument that is a bit smaller, and hence suitable for people who, historically, have been a bit smaller," he says. "But now you hardly see those instruments, as if we must all obey the machine, as if it is us who must accommodate to exacting measures."

Karen Francois, a philosopher of math at the Free University Brussels, agrees that the study showcases the enduring worth of body-based measuring. "It has value for human problems on human scales," she says. "It's local knowledge, its ergonomic, it's technical, and it's still used."