Step off a edge or walk over a stone or yet to balance your heels and suddenly your ankle twists. At once, your arms flail and your body jerks as you strain to catch your balance. Such trip-ups can be painful and embarrassing. But often the culprit is not clumsiness.
Come to think of it, Traveling upright (on two feet) is only peculiar to humans, no other mammal does it.
As our ancestors evolved, they began to walk on two feet instead of four. This freed up their hands to make tools, to hunt and to carry their young. But those advantages came at a price – stresses on the legs, feet and back.
Flat feet, sprained ankles and slipped disks all trace back to moving around on two feet, not four. These particularly human maladies all stem directly from our becoming two-footed, upright walkers.
This adaptation has required some painful compromises.
Upright walking is considered one of the earliest and most important steps that our species took in becoming human.
It is natural then to ask why it leads to pain in so many people today. For all its adaptive advantages, evolution does not produce perfection.
Rather than starting from scratch to build a body made for hiking and running, evolution instead works with the genes and traits at hand to reshape a species. In our case, that meant transforming an ancient ape’s body, designed for living in trees, into a human body more at home on the ground.
Natural selection has done a good job in this conversion, it’s good enough to have helped humans survive and ultimately dominate their ecosystem, but it’s not so good that we don’t also suffer some consequences.
During evolutionary change, humans took
the same amount of bone mass that a chimpanzee or gorilla has, and spread
it over a larger area. This made the bones in our backs less dense and less strong. It also means
that as people approach middle or old age, those vertebrae can begin to give out. These bones, as well as others, often weaken and become brittle (another common injury in the elderly), hip fractures also can be
traced to the loss in bone mass. Weak and wobbly spines are one thing, but a lot more happens when
you remodel an apelike foot into a human’s.
Chimpanzees, gorillas and other primates have 52 foot bones, or 26 in
each foot. They need all these to maintain the flexibility needed for a
foot to grasp well and climb. Strolling around on two legs requires more stability. So over millions of years, evolution slowly converted a mobile, grasping foot into a stiff and rigid one that didn’t require 26 bones. To cope, the hominid body adapted by altering the angle of a bone here or it turned a curved bone into a flat one somewhere else. Most of those changes were quite
Another change over time was that some foot tissue thickened to form a ligament – anterior talofibular ligament, it resembles an elastic band. This ligament holds bones together at the
ankle. The extra stability it offers helps people walk on two feet. But this solution has proven far from ideal. When people step the wrong way, the foot may twist to the side.
This can cause a sprain. The problem plagues athletes in many sports,
especially basketball and soccer. In fact, the anterior talofibular is the
most-often sprained ligament in the entire body. It’s a problem chimps will never experience because they don’t have this tissue. In fact, having this ligament would make it hard to twist in ways needed
to support their climbing.
Other foot problems trace to far more
modern habits, such as wearing shoes. When laced up in shoes, foot
muscles don’t need to work as hard as they do when our feet are bared. Overtime, shoed feet may lose their power. Then, when someone walks barefoot or stresses the feet, a stiff and painful
condition can result. It’s known as collapsed arches.
As humans evolved, their brains also enlarged and became more complex.
Over the course of human evolution, the brain tripled in size. To make room for this extra tissue, the shape of the
face and head changed time as well. Weird as it may sound, these changes left less room for some teeth known as wisdom teeth, these molars emerge at the back of the mouth often near the end of adolescence.
Early hominids relied on this spare set of molars to substitute for teeth that had been worn down by chewing a diet of roots and nuts. Humans no longer need these bonus teeth. In fact,
wisdom teeth can prove a nuisance. If the jaw lacks room for them to grow in
properly, intense pain or an infection can develop. That’s why dentists often remove these extra teeth.
But it wasn’t just the human brain and skull that changed in size and shape. As bodies adapted to upright walking and bigger brains, females’ bodies changed to make room for their large-brained babies.
Although they may seem tiny to first-time parents, human newborn babies
are actually big, relative to their mothers. For instance, newborn gorillas, on average, are only 2.7 percent as big as their mothers. Chimps, at birth, are 3.3 percent of
their mother’s size. Human babies?
They’re a whopping 6.1 percent as big as their moms.
To accommodate larger babies, a woman’s pelvis had to widen and deepen. The birth canal also changed shape. In chimps and other nonhuman primates, the oval-shaped
birth canal is broad and flat from beginning to end. This allows a baby
chimp to shoot through the canal in a straight shot at birth. In people, the birth canal is different. It starts out broad and flat. Then,
halfway down, it narrows and lengthens. To exit through this birth canal, human babies must turn along the way, rotating 90 degrees.
This rotation makes it possible for moms to push large babies through
their pelvis as they give birth. But it also makes it harder for them to give
birth without help from others. This change easily might have lead to disaster. After all, other primates generally give birth without assistance.
Blame evolution for why sprained ankles, hip fractures and other physical problems plague people.