The origins of humanity is a subject that has fascinated me since I was a child. And ever since I started to try and keep up with the dizzying pace of discoveries about who our ancestors were and other mysteries of our species, I have been interested in reading about the great debates that have roiled the scientific community regarding how we got to be who we are; tool making hominids who can think, reason, plan for the future, and create wondrous pieces of art that represent the pinnacle of evolutionary achievement on this planet.
But how did we get from a point that evolutionary biologists believe could have been 8 million years ago when our species separated from other apes and where we began the long, tortuous journey to who we are today?
One of the major milestones in that journey occurred when for some mysterious reason, our ancestors stood up and took the first tentative steps that freed their hands to do other things. This was an extraordinary long process that could have begun as long as 5 million years ago. The reasons why have been the source of some of the most fascinating speculation in science. Did the climate change the landscape from a tree-choked jungle to grassy Savannah which would have forced our ancestors to move quickly across the vast expanses of grassland in our search for the fruit and fodder that made up our diet at the time? An upright walker would have had an advantage because the broiling sun and searing heat (it was much warmer back then) would have been much harder on a creature that walked on all fours. Less of the body is exposed when walking upright thus allowing for more efficient cooling.
Or perhaps it was a combination of environment and mutation with evolution gradually favoring creatures whose pelvic structure allowed for longer and longer periods of upright walking. Over several thousand generations, it is conceivable that these barely noticeable changes would have added up to an ancestor who could walk as we do.
It is extremely unlikely that our distant ancestors just got up and started to walk one day. The radical differences between human locomotion and how chimps and other Great Apes move prove that there must have been several interim means of getting around – not quite walking the way we do but not moving about on all fours.
What we’re sure of is that by 3.2 million years ago, that evolutionary change led to a 3 foot tall female hominid whose pelvic structure and leg bones allowed for what we would most certainly recognize today as walking upright. Her name is Lucy. She was discovered in Ethiopia by a team of archeologists led by Dr. Donald Johanson. Other ancient hominids have been found in an ancient river bed near an open wound in the earth’s crust known as Olduvai Gorge in northern Tanzania. The gorge has been a godsend to archaeologists because some long ago cataclysmic earthquake split the ground in such a way as to reveal how the earth looked millions of years ago. Walking around the gorge is like walking in the footprints of our earliest ancestors.
The discovery of Lucy back in the early 1970’s ignited a debate that rages to this day; what kind of a “walker” was she?
Dan Gebo believes that if we could go back millions of years and see hominids, the early, small-brained humans from which modern humans inherited the ability to move around on two legs, we would see some pretty peculiar styles of walking.
The hominid nicknamed “Lucy,” a 3 1/2-foot-tall adult female who lived in what is now Ethiopia 3.2 million years ago, tired easily and would have had to run at a dead trot to keep up with a strolling modern human. And Australopithecus robustus, a toothy, dim, broad-faced early human that went extinct 1.4 million years ago, was hopelessly knock-kneed.
But these walks, however imperfect, were the most important steps ever taken for humankind, said Gebo, a Northern Illinois University anthropologist and co-author of a new study of the biomechanics of early human locomotion.
A. Robustus was an interesting fellow in that he lived during a time of enormous environmental stress on the hominid population. The habitat for our ancestors was probably changing into near desert conditions and Robustus – a little larger than we are with a much smaller brain – was nevertheless able to survive by eating extraordinarily tough roots and probably equally hard to chew tubers. He was able to do this with a jaw twice as massive as our own and molars the size of quarters.
But what about Lucy?
Current thinking is that the first hominids to use two legs had feet similar to those of modern humans and therefore walked in the same way. Gebo and Schwartz say hominids’ foot anatomy evolved in subtle but significant ways over millions of years before they walked like modern humans.
The duo came to their conclusions, which some of their colleagues do not entirely accept, after reassessing the hominid fossil record, comparing them to modern humans and apes.
“I study how animals move,” said Gebo. “I want to know the exact sequence of changes leading to bipedalism. What happens first? Do we lose the graspable big toe of apes, or do we get long legs or a different pelvic structure first?”
Gebo is convinced that Lucy would have had a hard time keeping up with modern humans:
Australopithecus afarensis, a fossil nicknamed Lucy when 40 percent of her skeleton was found intact in Ethiopia in 1974, in life was a wimp compared to humans in terms of standing for long periods or walking long distances, said Gebo.
She had the same bones in her feet as modern humans. The difference is that many of the human foot bones are fused, but not Lucy’s. She had to rely on muscle to stabilize the bones for efficient walking and standing, causing her fatigue humans don’t experience.
“Lucy had a sort of kiddie-stride, because her legs were so short,” said Gebo. “It’s like comparing the horse versus the pig stride. Pigs can move just as fast, but they have to move their legs much faster. Horses are great long-distance runners, but pigs are not.”
Other scientists have pointed out that Lucy may also have been much more unsteady on her feet given that her sense of balance was probably not quite as developed as ours. Her inner ear mechanism could have been vastly inferior to our own thus causing her to walk with her legs much farther apart to maintain balance over long distances.
So if Lucy was able to stand up, why wasn’t she capable of making tools? This is one of the biggest mysteries of all because as it turns out, there are other factors that speak to tool making not the least of which is the old adage “necessity is the mother of invention.”
As long as we were berry eaters, there was no real need for tools. But when environmental factors put pressures on our food supply, it is possible that we became hunters but more likely scavengers, eating the dead carcasses of other animals. This increase in protein in the diet has been the subject of fierce debate because some scientists believe that eating more meat meant growing a bigger brain. The bigger the brain the larger the head. The larger the head, the bigger the female pelvis would have to be to allow for babies to be born. And the larger pelvis led to more efficient walking. The better walkers would become good runners which increased our skills as scavenger/hunters. Leading to more protein in the diet and the circle continues.
Controversial, but fascinating.
The work being done by Dr. Gebo and others in this field is revealing in that for the first time in our history, we are looking at some of the deepest mysteries as to how we evolved to become modern humans. The answers will not come in our lifetimes. Nor will the end of the questions for that matter. But it is the process of discovery itself that contributes to our understanding of what makes us human.
And that’s a quest I’m sure to enjoy for as long as I’m alive.