Demystifying science | The future of the little toe

Each week, our journalist answers scientific questions from readers.

Are we going to lose our little toes because of evolution?

B. Tremblay

No. But it has been noticed for some time that two of the three phalanges of the little toe are often fused in modern populations.

This phenomenon is called “biphalangy”. “Biphalangy is remarkably high,” says Campbell Rolian, an anthropologist at McGill University, who published a 2009 study of toe shrinkage 1.5 million years ago in the Journal of Experimental Biology. “It exceeds 80% in Japan and 40% in the United States for the little toe. It is not known, however, when the merger occurs. Do babies have biphalanges of the little toe before they start to walk? »

Do today’s hunter-gatherers, for example those of the Amazon or the African forests, have so much biphalangy because they don’t wear shoes? “We don’t know, we need a study in this population,” says Caley Orr of the University of Colorado, who has published several studies on the evolution of the foot and the hand.

“I don’t think biphalangy is a product of recent evolution. There does not appear to be any functional advantage for the individual wearing shoes. For there to be evolutionary pressure, there needs to be a functional advantage. It is possible that biphalangy is negative for walking when barefoot, but not [moins] when you have shoes. But that remains to be demonstrated. »

When we walk, we use our four “lateral” toes to keep our balance and the big toe to propel us forward, Rolian explains.

Nevertheless, the question of the possible disappearance of the little toe fascinates ordinary mortals. The three specialists in the evolution of the foot in hominids consulted by The Press are unanimous on this point. “My students often ask me this,” says Matt Tocheri, an anthropologist from Lakehead University in Ontario, in an interview from Java, where he’s working on Homo floresiensisthe “hobbit” discovered in 2003 in Indonesia.

Between 1.5 and 2.6 million years ago, the ancestors of modern man saw a major transformation on their toes: they became smaller, which made it easier to walk upright, and especially to run. .

“Primates have longer toes to be able to climb trees,” says Tocheri, author of a study on the subject published in 2018 in PNAS. “They can use their feet to manipulate things, like a hand. Moreover, primates are the only mammals that have all kept five fingers and five toes. The horse, for example, no longer has five fingers, but only one hoof, cats and dogs have four fingers on their hind legs. »

Still, are little toes really necessary for walking? “Instinctively, I think so, but we would have to check with a group of people who have had the amputation of the little toe,” says Mr. Rolian. And the studies on diabetics, who sometimes have to have their toes amputated, focus on people who have lost the big toe. »