In 2007, Jan Souman dropped three volunteers into the Sahara desert and watched as they walked for several miles, in an attempt to walk in a straight line. Souman was interested in the widespread belief that lost travelers end up walking in circles, a belief that has never been properly tested but has nonetheless become firmly entrenched in the popular consciousness. Just think about Frodo and Sam’s hike through Mordor or the three hapless teens in the Blair Witch Project.
To see how non-fictional humans would fare, Souman tracked a group of volunteers using GPS as they walked through a thick German forest or a featureless Tunisian desert, as well as others who strolled through a large field blindfolded. The result: they did indeed go in circles but with no preference for any direction and only when they couldn’t see or when the sun or moon weren’t visible.
It seems that with some sort of reference point, we’re entirely capable of walking in a straight line, even in a featureless desert where dunes obscure the horizon or a busy forest that’s riddled with obstacles. The sun’s good enough for these purposes, even though it’s position changes as the hours pass. Without any such cues, we quickly veer off course.
The two volunteers who walked through in the forest on a sunny day managed to keep to a perfectly straight line, wandering only in the first fifteen minutes when the sun was behind a cloud. The four people who walked on much cloudier days all ambled in circles, repeatedly crossing their own path without knowing it. The desert walkers fared about as well – those who walked during the heat of the day veered slightly but kept reasonably straight. A third man walked at night; he too kept a direct course when the moon was visible but when it vanished behind clouds, a couple of sharp turns sent him back in the direction he came from.
Scientists have put forward many explanations for the circular rambles of lost walkers. Some say that most people have one leg that’s longer or stronger than the other and over time, these differences add up to a curving course. Others say that asymmetries in our very brains set up a tendency to turn in one direction. Without a guiding light or landmark, these small biases would make their presence felt.
But Souman thinks otherwise. He set a group of 15 blindfolded people loose in a large field, told them to walk straight ahead and watched them for 50 minutes. All of them walked in very random paths, including large flamboyant loops and, on occasion, surprisingly small circles of as little as 20 metres in diameter (little enough to fit within a basketball court).
Seals and sea-lions gracefully careen through today’s oceans with the help of legs that have become wide, flat flippers. But it was not always this way. Seals evolved from carnivorous ancestors that walked on land with sturdy legs; only later did these evolve into the flippers that the family is known for. Now, a beautifully new fossil called Puijila illustrates just what such early steps in seal evolution looked like. With four legs and a long tail, it must have resembled a large otter but it was, in fact, a walking seal.
Natalia Rybczynski unearthed the new animal at Devon Island, Canada and worked out that it must have swam through the waters of the Arctic circle around 20-24 million years ago. She named it Puijila darwini after an Inuit word referring to a young seal, and some obscure biologist. The skeleton has been beautifully preserved, with over 65% of the animal intact, including its limbs and most of its skull.
Puijila is a massive boon for biologists trying to understand the evolution of pinnipeds, the group that includes seals, sea lions and walruses. It’s not itself a direct ancestor, having branched off the evolutionary path that led to modern pinnipeds. It did, however, retain many of the same features that a direct ancestor would have had. “Puijila is a transitional fossil,” Rybczynski explains. “It gives us a glimpse of what the earliest stages of pinniped evolution looked like, before pinnipeds had flippers. And it suggests that in the land-to-sea transition, pinnipeds went through a freshwater phase.”
This familiar group evolved from land-dwelling carnivores and their closest living relatives are the bears and the mustelids (otters, weasels, skunks and badgers). For other marine mammals like whales and dolphins, the fossil record has given us dramatic visuals for the gradual transformation from land-dweller to full-time swimmer. But for pinnipeds, that transition is much murkier because until now, the earliest known seal Enaliarctos already had a full set of true flippers. Puijila changes all of that.
In the Origin of
the Species, the ever-prescient Darwin wrote, “A strictly terrestrial animal, by occasionally hunting for food in shallow water, then in streams or lakes, might at last be converted into an animal so thoroughly aquatic as to brave the open ocean”. This year, on the 150th anniversary of the book’s publication, the walking seal that bears his name pays a fitting tribute to Darwin’s insight.
Walking on two legs, or bipedalism, immediately sets us apart form other apes. It frees our arms for using tools and weapons and is a key part of our evolutionary success. Scientists have put forward a few theories to explain how our upright gait evolved, but the ‘savannah theory‘ is by far the most prolific.
It’s nicely illustrated by this misleading image that has become a mainstay of popular culture. It suggests that our ancestors went from four legs to two via the four-legged knuckle-walking gait of gorillas and chimps. Dwindling forests eventually pushed them from knuckle-walking to a full upright posture. This stance is more efficient over long distances and allowed our ancestors to travel across open savannahs.
But this theory fails in the light of new fossils which push back the first appearance of bipedalism to a time before the forests thinned, and even before our ancestors split from those of chimpanzees. Very early hominins, including Lucy (Australopithecus afarensis) and Millennium Man (Orrorin) certainly ambled along on two legs, but they did so through woodland not plains.
Our arms provide a further clue. Even though our ancestors’ back legs quickly picked up adaptations for bipedalism, they steadfastly kept long, grasping arms, an adaptation more suited to moving through branches. To Susannah Thorpe at the University of Birmingham, these are signs that bipedalism evolved while our ancestors were still living in trees. And she has found new support for this theory by studying Sumatra’s orang-utans, who occasionally take to two legs to negotiate tricky canopies.