Let’s take a walk, said one future-man to his partner. But, was that a good idea? And, why did he get this Eureka moment? Well, as the old cliché goes – let’s take a walk down memory lane, or meander down a back lane, into the dim and hoary past. When our forebears thought it a great idea to stand up and reach for the stars…or at least the tops of tall trees!
Are four legs better than two? Is evolving from four legged mammals to two legged, upstanding examples of humanity, the reason why our human skeleton has found it difficult to deal with the stresses and strains of modern life? Let’s look back at the evolutionary story that has brought us to where we stand today.
“Hey! I can stand up and walk…!” said H. erectus, 1.89 million ago…
“When our earliest ancestors started walking on two legs, they took the first steps toward becoming human,” said lead researcher Michael Sockol of UC Davis, Jul 20, 2007. According to Sokol, “Fossil and molecular evidence suggests the earliest ancestors of the human family lived in forested areas in equatorial Africa in the late Miocene era some 8 to 10 million years ago, when changes in climate may have increased the distance between food patches. That would have forced early hominids to travel longer distances on the ground and favoured those who could cover more ground using less energy.”
As per the Smithsonian’s Science/Nature magazine (Aug 6, 2012) , “It’s not until the emergence of H. erectus 1.89 million years ago that hominids grew tall, evolved long legs and became completely terrestrial creatures. While the timeline of the evolution of upright walking is well understood, why hominids took their first bipedal steps is not.”
Walking on two legs separated the first hominids from other apes, but scientists are still scratching their heads over why our ancestors became bipedal. Bipedalism evolved well before the large human brain or the development of stone tools. Bipedal specializations are found in Australopithecus fossils from 4.2-3.9 million years ago, although Sahelanthropus may have walked on two legs as far back as seven million years ago.
Let’s consider that most fundamental aspect of human behaviour: walking upright.
In the 1920s anatomist Raymond Dart discovered the skull known as the Taung Child in South Africa. This skull had had a small brain, hence many researchers were of the opinion that the approximately three-million-year-old Taung was just an ordinary ape. But one specific feature distinguished the Taung as being human-like. Looking closely at the skull, researchers saw that the hole through which the spinal cord leaves the head, was further forward under the skull as compared to an ape’s. This was an indication that the Taung used to hold his head erect and, hence, most likely used to walk upright. More fossil discoveries of bipedal apes – the ones that predated Neanderthals and H. erectus (collectively known as australopithecines) – caused anthropologists to conclude that walking on two legs actually came before big brains in evolutionary history.
Then, there was Lucy!
In 1974, anthropologists found Lucy! An almost complete australopithecine skeleton. Lucy was small, but she had the anatomy of a biped – broad pelvis and thigh bones that angled in toward the knees, bringing Lucy’s feet in line with the body’s centre of gravity. This is what gives humans critical stability while walking. Simple! But, it appears that bipedalism has very ancient roots.
- In 2001, a seven-million-year-old Sahelanthropus tchadensis was discovered in Chad. Sahelanthropus‘ status as an upright walker is based on the placement of its foramen magnum
- In 2000, the teeth and two thigh bones of the six-million-year-old Orrorin tugenensis.paleoanthropologists was found in Kenya. The shape of the thigh bones confirms Orrorin was bipedal
- The 4.4-million-year-old Ardipithecus ramidus is the earliest hominid, offering the most extensive evidence of bipedalism
Though capable of upright walking, the earliest hominids didn’t actually get around the way we do today. It wasn’t till the emergence of H. erectus, 1.89 million years ago, that hominids grew tall, evolved long legs and became totally terrestrial creatures.
Darwin’s take on why we took to our heels!
In 1871, Charles Darwin offered an explanation as to why man decided to stand up and starting walking around on two limbs instead of four. In his book The Descent of Man, Darwin says: “…the hands and arms could hardly have become perfect enough to have manufactured weapons, or to have hurled stones and spears with a true aim, as long as they were habitually used for locomotion.” One issue with this idea is that the earliest stone tools didn’t show up until roughly 2.5 million years ago, about 4.5 million years after the origin of bipedalism’s.
Another theory concerns the efficiency of upright walking. Peter Rodman and Henry McHenry, University of California, have suggested that hominids evolved to walk upright because of climate change. As forests shrank, our hominid ancestors had to descend from the trees to walk across the ever-growing swathes of grassland that lay between forest patches. The most energy-efficient way was to walk on the ground, on two legs.
The eternal question of why and how bipedalism evolved might have more accurate answers if paleoanthropologists dig up more fossils of the earliest hominids, that lived seven million to six million years ago. Who knows how many more species of bipedal apes we might discover. But, with each new find, we might also find evidence that has the potential to change how we comprehend the origins of one of our most distinctive characteristics, walking on two legs.