New Under the Sun:
Volume 6, Issue 5
Walk, Don't Run!
Why do we walk on two legs?" "So that we can run faster!" answer many college students. Other answers are also given, but the "running faster" answer always gets strong agreement from the students, who seem to feel it makes perfect sense. As you are reading this, you might also believe it makes perfect sense. After all, it is obvious that humans can run very fast. We long ago broke the four-minute mile barrier. Runners can do a marathon in slightly over two hours. Clearly, humans, at least some of them, have very fleet feet.
But if running fast were an important adaptation for our species, we would have remained at least semi-quadrupedal, as are our relatives, the great apes. Furthermore, if running our prey to the ground were the hunting method of choice of our earliest ancestors, the fully quadrupedal adaptation of baboons would have been far more appropriate than the bipedal stride that we have instead. Baboons successfully co-opted the niche of savanna primates who either hunt as individuals by the fast snatch and grab method, or use a relay team of a small group of males to run their prey to the point of exhaustion, at which time they move in for the kill. Human bipedality, moving around on two legs, is simply not as efficient as quadrupedality, moving on all fours, in these circumstances. In that case, what is the point of bipedality?
The skeletal remains of the earliest hominids, our bipedal ancestors, are found in or near ancient lakes, streams, and swamps. In part, this is due to the fact that skeletal material is more likely to fossilize in still water than on land. A hominid who died on the savanna would have been quickly torn apart by scavengers. The bits and pieces that remained would be exposed to the destructive effects of sun, wind, and rain. Any skeletal pieces not destroyed by weathering would have been pulverized by herds of elephants and wildebeests. Given these destructive events, it is not too surprising that most of the hominid remains we have come from what were ponds, lakes, or still streams where the dead individual would have been hidden from scavengers and quickly covered with silt.
While there is a bias towards finding fossils in areas that had once been the edges of lakes, streams, or swamps, these environments also may have played a major role in the development of bipedality. Quadrupedal locomotion is obviously a very successful adaptation since almost all land-based mammals are quadrupeds or semi-quadrupeds. Therefore, there has to be a significant change in the way in which our ancient pre-human ancestors interacted with the environment that would propel them along the path of adaptation to bipedal locomotion.
Fish, Shellfish, Eggs, and Bipedality
The earliest hominids had small brains, much smaller than our own. The brains are near in size to those of chimpanzees, but somewhat larger. It may well be that this small, but important increase in brain size is directly associated with the development of bipedality. Omega-3 fatty acids and protein are important to brain growth and development. Fish and shellfish are excellent sources of omega-3 fatty acids, eggs have varying levels, and all three are high quality sources of protein.
The edges of lakes, streams, swamps, and seacoasts are rich sources of easily gathered foodstuffs. Nesting waterfowl provide an easy supply of eggs, not to mention the occasional bird. Fowl who have a diet heavy in fish and shellfish have higher levels of omega-3 fatty acids in their eggs than do other fowl. The various plants edging the shores offer a diverse source of nutrients. Shellfish and fish can be easily collected from shallow pools. For instance, a hominid ancestor would discover that dragging a scavenged bone that had bits of attached flesh through the water was a simple way to catch crabs. The crabs would be attracted to the meat and latch onto the bone. The collection of these rich and diverse foodstuffs is made much easier if one is willing to wade out a few feet from shore and continue wading along the shoreline. It is far easier, and the results of the efforts are more successful, if the wader moves bipedally.
Origins of Bipedality
Although most chimpanzees are not fond of wet environments, bonobo chimpanzees frequently travel through swampy regions in their search for food. Beginning around 8 million years ago, the environment of our earliest ancestors was changing from a densely-forested one to one with more sparsely-forested areas separated by and surrounded by grasslands watered by lakes and streams. For females with young ones, the most easily-gathered resources would be along the shores of lakes and streams. But in order to do this effectively, especially if the female had an infant, it would require that she move along the shores bipedally.
The Japanese macaques on Koshima Island began, in the 1950s, to use seawater to wash their food. Later, they taught themselves how to swim, both by paddling with their head above the water and by swimming under the water. Swimming is now a frequent activity on hot days. Both washing food and swimming began with juveniles and their mothers. It seems probable that gathering foods by wading along the shore would begin with the juveniles and mothers of our earliest ancestors. As generations passed, this method of obtaining food would become a normal activity for all group members. Those individuals who could wade most easily along the shore would be the most successful. They would obtain the best foodstuffs, would be the healthiest, and would leave the most offspring. Their successful genetic traits would be passed on to future generations, while those who were less successful at bipedal wading would leave fewer offspring; gradually, their genetic traits would cease to be passed to future generations. Over many thousands of years, the waders would become more and more bipedal until finally they were fully adapted to bipedality and were then hominids.
Due to their diet rich in fish, shellfish, and eggs, these hominids also had larger brains and were smarter than their chimpanzee relatives. This increased intelligence, although slight, was enough to set into motion the development of the hominid line that eventually led to us. However, this was a very slow, gradual process; a process that could have ended at any point in time if the environment changed too rapidly for our ancestors to adapt. Our existence was not foreordained.
Standing upright and moving around on two legs is more energy-efficient if the thighs angle inward under the hips, placing the legs under the torso instead of to the sides of the torso, as is the case when chimpanzees walk bipedally. For individuals who needed to be bipedal during food gathering activities, those whose legs had a somewhat more inward angle would use less energy in obtaining food than would those whose legs were more perpendicular or straight down from the hip joint. Less energy used for food gathering meant more energy to devote to other activities such as mating and child rearing. Therefore, the more bipedal an individual was, the more successful he or she would have been as measured by having more of their offspring survive.
Among tropical/subtropical foraging populations, 60 - 70% of the food is provided through gathering activities. Gathering does not require speed, but it does require efficiency and stamina. Even most hunting activities primarily require efficiency, stamina, and stealth to track game over long distances, kill it, and carry it back to the home base. Once our hominid ancestors were fully bipedal and began expanding their territory into more varied environments, they would have spent most of their day in walking from one food site to the next, gathering various items, eating them along the way. On the rare occasion when an animal was caught and killed, the group might gather to share the meat, as happens among chimpanzees. However, on most days, food would have been gathered by wading along the shorelines to collect eggs, shellfish, fish, and waterfowl; picking berries from bushes; digging for tubers; gathering fallen ripe fruits and nuts; and, possibly, climbing trees for other fruits and nuts. Speed was not necessary, but an efficient, steady walking pace from one food site to the next was.
Our hominid ancestors probably walked several miles each day in their quest for food. Running, particularly for adult females, played very little role in their daily activities. In fact, the wide hips of women, necessary for easing childbirth, make running inefficient and even awkward. Running also puts tremendous stress on feet. If feet and ankles become injured, then food collection activities become more difficult, putting the individual's life at risk.
Even for hunters, strategy and stealth were more important than speed. Group hunting by West African chimpanzees involves driving the prey in a particular direction while blocking escape routes. Only at the very end, when the prey reaches the "collection" point, is speed necessary. Prior to that, the chimps move at a steady, quadrupedal walking pace. Based on the evidence presented here, we can conclude that our major form of exercise should be walking, and that we should try to walk several miles each day.
Exercise and Health
Other forms of exercise can be beneficial, but, except for swimming, the other forms tend to put undue stress on our joints and cause repetitive motion injuries. The knees are particularly easy to injure. Chimpanzees have a more stable knee joint than do humans because the thigh bone meets the leg bone squarely: there is no angle between the two bones. On the other hand, the human thigh bone is sharply angled relative to the leg bone. This angle, while making bipedal walking more efficient, also makes the knee joint more vulnerable to twisting and to torn ligaments. Our bodies were modified for walking.
The adaptation for bipedality, swinging the legs under the torso, also streamlines our bodies for efficient swimming. The buoyancy of water prevents undue stress on our joints. Therefore, swimming is also an activity for which we are adapted. It is probable that, as with the Japanese macaques, our hominid ancestors also enjoyed a cooling swim on occasion, interspersed with their gathering/wading activities.
Walking and swimming are low impact activities that individuals of any age can participate in to improve overall health. They are also the activities, especially true of walking, that were most frequently engaged in by our hominid ancestors. During the course of each day, our ancestors did a great deal of stretching while obtaining their food and taking care of young. This stretching kept them agile and flexible. Unlike our ancestors, we can do an entire day's work while barely moving from the computer desk. Because of this, we tend to be much less agile and flexible: our muscles and joints are tighter and do not move freely. In order to correct this, we need to begin each day with a series of flexibilities: exercises designed to keep the muscles stretched and the joints loose. At first, you may be so tight, that you can barely move in some of the suggested positions. Keep at it and you will gradually loosen up and will be able to stretch further and further. In order to maintain this flexibility, the exercises must be done each day, preferably soon after rising. The exercises will get rid of the kinks that occur during sleep. Let's get real, flexibility is part of good health. You need to do it, so start tomorrow morning and do it every day.
Sit on the floor. Stretch your legs wide apart in the biggest V you can make. Reach for your feet. Eventually, you will be able to grab the soles of your feet. Hold this position without bouncing, and without undue pain, for a slow count of 20. Release.
In the same position, angle your entire body towards your right leg, attempting to grasp your right foot with both hands. Hold for a slow count of 20. Release.
Do the same for the left leg.
With legs still in V shape, cross arms in front of chest and lean torso over as far as possible towards the floor. Hold for a slow count of 20. Return to upright position.
Bend legs and bring them towards the torso. Bring the feet together and try to bring them as close to the crotch as possible. Hold for a slow count of 20. Release.
Still sitting, let legs loosely cross. Bend left arm behind back, reaching towards neck. Raise right arm, bend elbow, reach behind neck. Attempt to clasp hands. Hold for a slow count of 20. Release. Reverse position of arms, attempt to clasp hands, etc.
Still sitting, push legs forward with feet together and knees bent. Legs should form a diamond shape. Bend torso towards feet, attempting to touch forward to toes. Hold for a slow count of 20. Release.
Still sitting, bring legs together straight in front of you. Bend forward at waist. Attempt to grasp feet. Hold for a slow count of 20. Release.
Lay back. Bend right leg, bringing foot towards shoulder. Stretch arms above head. Hold for a slow count of 20. Release. Stretch out right leg and bring up left leg. Hold for a slow count of 20. Release.
Lay flat on back with legs stretched out in front and arms stretched above head. Hold for a slow count of 20. Release.
Laying flat on back, raise left leg. Grasp around thigh and pull gently towards shoulder. Hold for a slow count of 20. Release. Do the same with right leg.
Still on back, raise both legs. Grasp and gently pull towards shoulders. Hold for a slow count of 20. Release.
Drop legs. Bend left leg and pull towards chest, pointing toes. Keep right leg straight, about 6 inches above the floor, toes pointed. Hold for count of 5, then flex feet, while maintaining position and hold for count of 5. Return to toe point and count of 5, then foot flex and count of five. Release. Reverse legs and repeat.
Stand up with hands on hips. Move left leg forward and slightly bend knees. Hold for slow count of 10. Reverse legs, etc. Repeat for both legs.
Raise arms to sides at shoulder height. Bend left leg and lean towards left. Hold for a count of 10. Stand straight, then bend right leg and lean towards right. Hold for a count of 10. Repeat for both legs.
Stand up with legs spread wide. Bend at waist, grasp feet. Hold for a slow count of 20. Release. . While still bent over, use both arms to grasp right leg. Hold for a slow count of 20. Release. Twist to left leg, grasp. Hold for a slow count of 20. Release.
Stand in front of a stair. Raise right leg and rest heel on stair. Hold for count of 10. Change to left leg. Hold. Repeat for both legs.
Once you are comfortable with the moves, the entire series of flexibilities can be completed in 10-15 minutes. You will feel more alert, relaxed, and limber.
Once you are loose and flexible, you are ready for walking or swimming. Exercise has many health benefits. Those related to weight loss and cardiovascular health are probably familiar. Women who maintain a high level of physical activity do not develop an age-related decline in their resting metabolic rate, although sedentary women do. Maintaining a higher metabolic rate allows active women to avoid the increases in body fat found among sedentary women. Move it and lose it. Fat, that is.
Interestingly, physical activity appears to aid in the prevention of Alzheimer's Disease. One study found that those who were inactive in terms of intellectual and physical activities were about five times more likely to develop Alzheimer's Disease. Those who are sedentary and spend their time watching TV are not only more likely to have excess body fat, they are predisposed to developing Alzheimer's Disease as they age. The dangers of a sedentary life-style have even led to the coining of a new disease syndrome: Sedentary Death Syndrome or SeDS. There may be 250,000 Americans suffering from SeDS who are running a high risk for a shortened life span and/or a life of diminished mental abilities.
Postmenopausal women who maintain an active lifestyle achieve many benefits. In support of the Alzheimer's study discussed above, another study found that older women who walked several miles each week suffered less cognitive decline than did women who walked very little. Number of miles walked each week by the women ranged from less than one mile to 18 miles. Each extra mile walked resulted in a 13% less probability of later mental decline. The more you walk, the better off you are. Similar benefits can be achieved by men, but they probably need to increase the number of miles walked compared to women. Since the weight-bearing exercise of walking aids in maintaining and even increasing bone mineral density (BMD), degree of BMD and osteoporosis can be indicators of cognitive decline. Of course, adequate blood levels of vitamin D are also necessary to maintain bone strength. Taking a daily walk in the sunshine will improve your mood and your health in multiple ways, especially since this is the best method for getting adequate UVB radiation exposure.
When planning your daily walk, take into account the time of the year, your skin color, and where you live. If it is summer in Phoenix and you have very light skin color, you should probably limit your walk to ten minutes without sunscreen. For longer walks, you should apply sunscreen to prevent burning. Since this will also prevent vitamin D production, you may need to schedule several short walks into your daily schedule. The appropriate amount of exposure should result in, at most, a minimal tan. For the person with very light skin color living in Seattle, you may be able to take 20-minute walks during the summer without needing sunscreen. In all cases, wearing a hat is recommended. This will protect your face and decrease skin wrinkling. However, since your face will be protected, this means that you may need to be out in the sun about one-third longer in order to activate enough vitamin D production from exposed, unprotected skin on arms and legs. Individuals with very dark skin color can and should take long walks in the sun each day without sunscreen on their arms and legs. Those living in the northern latitudes will also need to eat foods containing vitamin D and take vitamin D supplements since even the longest walks may not provide them with adequate levels of vitamin D.
Walking can increase bone mass, but swimming does not since it is not weight bearing. However, swimming does improve the strength of shoulder and back muscles. In addition, for those who have injured their ankle, knee, or back, water exercises can maintain fitness while the injuries heal. Alternating long walks with swimming laps will maintain all around fitness. These activities appear to be the ones for which our bodies are adapted.
Exercise is necessary, but very strenuous exercise over a long period of time can actually be detrimental to your health, particularly if you are a woman. Young female athletes are especially prone to problems resulting from the "female athlete triad." This triad is composed of diet and eating habits, the menstruation cycle, and bone strength and mass. Young women who are under intense pressure to perform at high levels tend to have eating disorders including bulimia and anorexia. The poor and inadequate diet, along with intense exercise, can cause menstrual irregularities including the complete termination of menstruation and ovulation. These factors can lead to inadequate bone mineralization with the result that women in their late teens and early twenties can have the bone mass and structure of elderly, osteoporotic women. This bone loss may be permanent even if hormonal therapy is begun.
Your body is adapted for walking. Our ancestors probably walked at least 20 miles each week during their food collection activities. Walking provides numerous benefits. It is low impact and so is unlikely to cause injury. Bone mass is enhanced since it is a weight-bearing activity. Cardiovascular fitness is maintained. It allows for vitamin D production through exposing unprotected skin to UVB radiation while on the walk. An active lifestyle also prevents a reduction in the resting metabolic rate so fat accumulation is avoided, and it is associated with a reduction in the incidence of Alzheimer's Disease.
Bipedal wading for food was probably the primary factor in the development of our bipedal posture. Having our legs under our torso also allows for efficient swimming. Since our ancestors spent time near water sources, it is probable that swimming was one of the activities they enjoyed. Swimming provides cardiovascular fitness and improves upper body strength.
Let's get real. Exercise is vital for good health. If you don't exercise, you put your health and even your ability to think clearly as you age at risk. So get out there and exercise! But make sure it is the exercise that is best for our bodies. To maintain good health while minimizing risk of injury, we should try to walk or swim at least two miles each day. Careful UVB radiation exposure during these exercise periods will also maintain adequate levels of vitamin D. These legs are made for walking!
© 2001-2009 Kathleen E. Fuller, PhD. All rights reserved.