For more on this topic, read the full article, Relationship between trackmakers of the Laetoli footprints from gait synchronization, by Wataru Nakahashi.

One day, you visit a museum and see an exhibit about Australopithecus. A couple of Australopithecus are walking together, with one arm draped around the other’s shoulder. It seems to be an exhibit modeled after the Laetoli footprint fossils. On another day, you go to a different museum and see another Australopithecus exhibit. This time, a parent and child Australopithecus are walking hand in hand. It also seems to be an exhibit modeled after the Laetoli footprint fossils. Wait, what’s going on here? Did the couple or the parent and child leave the Laetoli footprints? The truth is, no one really knows the relationship between the two individuals that left these famous fossils.

You take another look at the Laetoli footprints. Two footprints are aligned in parallel. There’s quite a difference in the size of the footprints, but the steps are very well synchronized. It seems the two individuals walked in sync with roughly the same step length. Given the difference in the size of the footprints, there must have been a significant height difference between them, but they still managed to walk in sync. They must have gotten along really well. Do humans today often walk in sync with someone who has a noticeable height difference? Do couples or parents and children tend to synchronize their steps more?

This study precisely aims to clarify this point. Using YouTube, a large number of videos of couples and parent-child pairs walking side by side with noticeable height differences were collected, and the frequency of gait synchronization was examined. Then, an astonishing discovery was made. Couples walking with one arm draped around the other’s shoulder very often synchronize their gaits, but parents and children rarely do. This suggests that the Laetoli footprints may have been left by a couple. Of course, humans today and Australopithecus are very different, but it’s an interesting possibility.

Authors biography: Wataru Nakahashi is an Associate Professor at Waseda University, Japan. He has been investigating human evolution for over a quarter of a century. He has a wide range of interests and conducts research on various topics, including bipedalism, life history, mating systems, the mind, culture, language, and society.

References: Nakahashi, W. (2025). Relationship between trackmakers of the Laetoli footprints from gait synchronization. Evolutionary Human Sciences.