Shanthala was on call and so Maya and I set out for an evening stroll. A neighbor walking their dog, still a puppy and not easily controlled, pushed us off our usual path. I walk Maya on the sidewalk, almost never crossing the street. I expected Maya to continue the routine. But, as we reached a traffic light on this new path, Maya stopped and gesticulated at the pedestrian crossing button, insisting that I press it. I was flabbergasted, I hadn’t realized how much she was imbuing when she was with us. I acted dumb and asked her what she wanted, to confirm that this was not a fluke. She pointed to the button and gesticulated again, this time more impatiently. After I pressed it, she gesticulated her desire to be picked up. Next, she pointed in the direction she wanted me to cross the street. I was even more surprised. This was the route when I took her running, but I didn’t think she would recognize and register this much information.
She demanded to be put down once we crossed the main street. From there, she walked all the way upto a neighborhood park. Walking with her is never a surgical operation. She stops many times along the way, examining the neighborhood, the passing cars, the passersby. She is happy to greet people who smile at her. A resident of one of the houses emerged with her 4 or 5 year old son and Maya rushed up to her, smiling and indicating that she wanted to hug the boy. All along the way, people stopped to admire this little girl, walking with such happiness.
Since Maya started walking when she was about thirteen months old, every day I take her for a walk around the block of our neighborhood. We’ve taught her to not pluck flowers, but to just touch them or smell them. So she just touches a flower or two in each bush and says “Ta”. When we get to a rosemary bush, she rubs the leaves and then rubs her face, her nose crinkling with pleasure. That spot is one of her two favorite stopping places on our walks.
Sometimes, Maya wakes up in the middle of the night and if I’m not around, starts whimpering before bellowing a full throated cry and starting her search for me. She realized that one of the spots I can be at is the toilet and so she checks there first. Before she could walk, she would crawl. Alerted by her quest by the baby monitor, I’d usually reach her before she had gone very far. Nowadays, she’s already waiting by the gate at the top of the stairs before I reach her. Since she has started walking, she rarely crawls. It is as if a switch has been turned on.
Why do we take so long to walk ? Walking involves maturation of both the muscles required and the sections of the brain responsible for controlling and coordinating the motion. The motor skills develop from head to toe i.e. we learn to control our face and neck much before we learn to control our hands and legs. Which is why babies can smile, stick their tongue out and hold their head up before they can sit, stand and walk. The motor nervous system is an incredibly complex piece of neural circuitry relying on a feedback loop to control the movements till they eventually become smooth. Many parts of the brain including the cerebrum, cerebellum and basal ganglia have to all mature before something as complicated as walking can occur. The whole process is quite hardwired i.e. little can be done by parents to accelerate it. Motor milestones (when the infants achieve a motor skill such as walking) are about the same across cultures as different as the Hopi Indians where infants are kept strapped to their mother’s back with little movement possible to modern middle class urban cultures where people attempt to give infants tummy time, kicking exercises and walkers.
Why did we start walking ? When did we start walking ?
The earliest known bipedal animal was a reptile whose fossil dates back to 290 million years. While dinosaurs and many birds (such as Ostrich) evolved to be bipedal, among primates, none are like humans in being exclusively bipedal; they’re bipedal for only some of the time. We had to undergo several structural changes to be bipedal, changes that prevent us from becoming efficient quadrupeds. For example, our hip joint is larger, shorter and broader than that of our primate cousins. Our toes are smaller, meant for motion rather than grasping as is the case with our nearest primates. One of the traits for classifying a fossil as an ancestral human (called hominins) is evidence of bipedalism. Until the discovery of the fossils of a creature named Orrorin tugenensis in Kenya in 2000, bipedalism was thought to have evolved around two to three million years ago. But this discovery dates this development around six million years old (the discovery also pushed back the split between chimps and hominins to seven million years).
We still do not know with certainty why we stood up and stayed up. Wikipedia mentions the existence of as many as twelve hypothesis that attempt to explain the origins of bipedalism. This article on Nova, the popular science show from PBS lists the various hypotheses. The one that I knew from a long time ago is called the Savannah hypothesis. As thick evergreen forests gradually disappeared and made way for wide swaths of grassland (savannah), staying on all fours with organs developed to hang from trees became less advantageous than walking. Standing up also allowed us to see farther. Another popular hypothesis is that walking endowed us with reproductive advantages. With our hands freed, we were able to carry back more food, thereby making the bipedal men more attractive to women. Another theory suggests that being bipedal allowed us to more efficiently conserve and dissipate heat. A biped apparently has a 60 percent reduction in the heat load compared to a similarly sized quadruped which in turn meant less water requirement. While many of these theories have fallen out of favor, the story remains without an end. Our bipedal origins remain a mystery.
A humorous aside. A colleague at work has this cartoon by his desk. I found this image courtesy of infiniteuser.
This evolutionary adaptation is not without its side-effects. My grandmother and my mother both suffer from severe arthritis, especially of the knee. I don’t remember my grandmother ever walking without limping, a sort of shitfing of weight to the outer side of the knee rather than directly on it, as she put one foot in front of the other. On days when her knee is tender, my mother walks like that now. Every once in a while, I take a gluosamine tablet because I’m afraid that with all my running and my mother’s genes, I’ll develop arthritis. Interestingly, arthritis has been discovered in the fossils of ancient hunter-gatherers. On Shanthala’s side, her mother suffers from severe lower back problem, something that flares up occasionally in Shanthala too.
Bipedalism also put us in conflict with our other singular characteristic, our rather large brains. Long, narrow pelvis gave way to short, wide hips to provide for a stable bipedal locomotion. This also narrowed the birth canal through which the baby had to squeeze through, putting both the mother and the baby at greater risk during delivery. We went from being gorillas with a 20 minute easy, almost painless labor to twelve hour labors, epidurals and C-sections. The small, flexible brains required for our narrow passage to the world, also meant that the brains in human infants needs a lot more maturation. Our brains continue to grow at a rapid pace, even after birth, hardly slowing down till we’re a year old.
So what came first ? The walking or the talking ? Lucy, possibly the most famous of all hominin fossils, along with much other evidence seems to indicate that bipedalism evolved before our larger brains. This is now generally accepted and some theories even argue that bipedalism may have spurred the evolution of larger brains.
Almost anything in our development can go wrong. Is there something that can make us become quadrupeds again ? In 2006, a Turkish professor, Uner Tan, reported the discovery of a family of 19 in which five individuals walked on all fours. Uner Tan dubbed the disorder, Unertan Syndrome. However, there is controversy over whether the behavior is caused by genetic defects or by the way in which they were raised. As Prof. Sean Carroll says on Nova: “The central question is not really whether a single mutation could lead some individuals to walking on all fours, but rather whether a single mutation could lead normal apes walking on all fours to walking upright. And this is completely invalid. From what we understand from both genetics and the fossil record, the process of becoming upright involved all sorts of changes in our ancestors, in our skeleton and in our musculature, in various parts of the body. And from what we understand about genetics of building those body parts and reshaping those body parts, it had to involve many genes and changes in those genes assimilated over a long period of time.”
In March 2008, an article was published in the Proceedings of the National Academy of Sciences in which the authors claimed: “Our data indicate that mutations in VLDLR impair cerebrocerebellar function, conferring in these families a dramatic influence on gait, and that hereditary disorders associated with quadrupedal gait in humans are genetically heterogeneous.” But the conclusions of this study have been refuted and there is general agreement that a single gene cannot be responsible for bipedalism.
Having reached the end of her rather long walk that Thursday evening, Maya sat down on the sidewalk by the Stop sign that marked 0.53 miles. I picked her up and carried her back to the house. But she was not done yet. She didn’t want to get back in and so we continued our walk around the block. Around the corner from our street, sprinklers came alive, spraying water onto the manicured lawns, spilling some onto the sidewalk. Maya ran towards the spray, stretching her hand out to feel the water. She looked at me and not seeing any sign of disapproval, waded into the middle of the lawn, screaming in delight at the water spraying her from all directions. I took her home a few minutes later. She was soaked, and deliriously happy.