I sometimes say that walking saved my life. That’s not the literal truth, but there were many days when it felt like that. Conversely, there were days when even walking around the grocery store felt like an impossibly painful chore due to hip osteoarthritis. My pain-free walks these days are a result of access to good health insurance & the 120+ year history of successful hip replacement surgery.
Most of our ancient primate ancestors didn’t live long enough to experience extreme osteoarthritis, although there’s some evidence that even dinosaurs had this common joint ailment. But walking did possibly save our ancestors’ life.
We are the walking primate. Scientists pretty much agree that the evolution of bipedalism in our ancestor primates between 4-7 million years ago (mya) set the stage for all the other anatomical changes that eventually led to us. According to Steven Jay Gould, bipedalism was “the prime trigger of human evolution.” Scientists also generally agree that climate change and a high degree of environmental instability during that time was a key factor which urged more of our tree-loving ancestors to get around more often by walking on their hind legs, in addition to, for a while, continuing to use their long arms for moving through the forest. Over these 3 or so million years, responding to many varied factors – including the acknowledged energy efficiency of bipedalism – these primates’ hind limbs & feet evolved into the hips, legs, & full-weight-bearing feet of australopithecines, our walking primate ancestors of about 2-4 mya, who differed from their tree-dwelling cousins primarily in their ability to survive & find food from a larger, more varied, & probably challenging territory.
Using those newly-evolved hips & feet, over time our ancient ancestors probably experienced how handy it was to be standing upright – appearing larger to predators, seeing further ahead - & having those other two ‘feet’ freed up to do other things…carry fruit, carry children, pick edible plants along the way…all factors which probably favored their survival into a next generation of walking primates. According to some, changes to these primates’ anatomy due to walking also may have changed incentives for sex and sharing. There were a number of different kinds of australopithicines and scientists keep discovering more, which keeps the story interesting! All of these kinds of walking primates eventually became extinct, but some managed to survive long enough to evolve into other species – similar to the fate of many other living creatures.
This very skimpy summary of millions of years of primate evolution would no doubt seem pedestrian to most scientists. I really appreciate that scientists who spend their lives studying the details of evolutionary biology often construct, based on their analysis of the facts, their particular narrative about the details of human evolution; I enjoy these stories & each one seems plausible. We’ll probably never know the whole story though, because it was so long ago that these evolutionary changes took place. But there’s no doubt that walking on two legs was key to how our kind of primate came about.
More to come about our more recent ancestor primates – homo erectus. They really got into the walking thing…about 2 million years ago some of them walked right out of Africa into ancient Asia & then eventually into Europe!