Sweet stems. Hot gams. Nice thighs. Women hear compliments like these everyday. Even men do too. It’s pretty obvious as we walk down the streets that we are a rarity; our legs can take up more than half our bodies. The gait of a human is unlike any other animal, including the apes we descended from. So, it’s hard not to ask: “Why are we walking on two legs instead of crawling on all fours?”
Picture yourself about sixty pounds lighter. You’re practically a raw vegan, you’ve skipped more than a few shave days, you’re crawling in the grass, and you’ve never read a book. This isn’t you on a cultish crash diet. This is you more than 5 million years ago before humans learned to walk.
How did we get from this root-chewing, tiny hairball to a six-foot-tall pedestrian rocking a short skirt? If crawling around on all fours worked so well for so many millions of years, then why the sudden change to standing up and strutting? What did early humans have to gain from climbing off the safety of their branches and taking a less-balanced, more-accident-prone stroll?
Today’s science has one concise answer for this: humans are lazy.
We can’t help it. We’re wired lazy. If our brain can avoid expending energy in any way, it will signal our system to do just that. And walking around on our knuckles was costing us too many calories.
Having more energy means a greater likelihood of survival. Homo sapiens are the only human-like animals from millions of years ago that survived into the present day. Bipedalism developed at an estimated 4.2 million years ago to save energy, and so, it saved our species. A key study reveals how much energy we look to save with our long legs. Researchers put chimpanzees on treadmills, training them to walk upright and on all fours, and compared their energy consumption through their breathing and their strides. They also put humans on the treadmills to measure them against the chimps. The results were fascinating. Walking humans were found to use only 25% of the energy chimpanzees use walking on all fours. Amongst themselves, chimps used a variable amount of energy whether they were walking on all fours or standing up. However, there was one chimp that used significantly less energy walking upright. What was different about this monkey? It had really long gams. Walking on two long legs is like the Energy Star solution to knucklewalking. So, longer legs, smaller muscles, thicker leg bones, and new hip structures evolved over time to build the perfect equipment for schlepping with the least effort.
We may have lost our speed, sense of balance, and upper body strength with our first step, but we had so much more to gain from bipedalism.
Now you are sitting here, on a man-made computer, reading a screen, being able to interpret symbols, analyze them, and then react to them emotionally. And to think, it was all because a monkey decided to stand up in the forest because it was lazy.
As the geography of Africa transitioned from dense forests to dry savannah, hominids had to travel farther from where they lived to get to their food source. Our stance evolved because it provided a better chance to get to our food. By standing upright, we are able to travel at greater distances, navigate harsher terrains, and able to carry back our food sources to our homes. All the while, we have a good view of the world around us and can be on the lookout for other food sources and potential threats. Since the first walker, we’ve become dependent on having two free hands with which to build tools and most importantly, feed our young. Just imagine your walk home from Trader Joe’s without the use of your arms. I can’t.
Standing up also proved to be an invaluable way to keep cool. Most creatures heat-regulating systems are their lungs. They can only cool down through breathing. Luckily for us, we have millions of sweat glands that soak our skin and drop our temperature. For ancient man, this meant he could outrun prey that needed to stop for a breather after a few miles. Also, a biped absorbs only about 60% of the heat an animal does on all fours. Our tall, lanky builds mean more breeze is distributed throughout our entire body and with less sun beating down on us, less water consumption is necessary. While these abilities aren’t tested today when we go to the grocery store to get our cereal and OJ, the remnants of our skills in persistence hunting can still be found in physical feats like marathoning. We can still outrun animals in terms of distance. Only our modern, slothful brains, ever the spendthrifts, tell us to stay at home, where the cabinets don’t require much of a chase.
Walking on two legs also meant more sexy times. No more, “Not now, honey, I have a headache from all that gathering.” We were spending less time on surviving through figuring out how to transport ourselves, hunt, and gather, and had more time for reproduction. Increased reproduction means a species has a better chance of longevity. Though nobody had Beyoncé-caliber stems just yet, early hominids were more enlivened with every step. With newly acquired bread-winning skills via walking and running, those who could walk looked even more appealing to their mates. Pretty soon those that had this desired skill were the ones to survive because they were the hottest by prehistoric standards. Then, those promenaders had babies, those babies had babies, and eventually, we were all walking.
There’s one last crucial gift walking upright has imparted on us. If it weren’t for our legs, we’d be a whole lot dumber, because our brains would never have needed to grow bigger, and thus, smarter. We have one of the largest body-to-brain ratios of any animal, so the human brain requires an amazing amount of energy. After we could walk, we engaged in persistence hunting, which allowed for a never-before-seen supply of meat at the ready. Our brains engorged with all that new animal power from protein and fats. It grew to be seven times larger than any other animal’s around it. And this thing needed a constant flow of fat and protein to sustain it, because it consumed 20% of the calories we take in alone. The one skill that really allowed for this huge brain to live on, and eventually naturally select itself into the every man: walking on two legs. Armed with a bigger hard drive, Homo erectus came onto the scene, developed tools with that big head and was able to live off what it hunted. Tool making and protein-heavy meats worked symbiotically to grow the brain and prepare it for the challenges of everyday survival.
And it worked! You’re the proof.
Today, a flash of a long, bare leg excites us. But, it should thrill our brains for a myriad of reasons. When ancient man decided to get swagger, we got swagger in the form of sustenance, transportation, and intelligence. Now you are sitting here, on a man-made computer, reading a screen, being able to interpret symbols, analyze them, and then react to them emotionally. And to think, it was all because a monkey decided to stand up in the forest because it was lazy.
ExpliKate is a column running on Kate-book.com every other Monday at noon. It is written by the hyper-inquisitive Kate Hakala, who seeks to answer questions ranging from “What is kombucha?” to what you read above. Follow her on Twitter here.