“Faut que je marche. Parce que je comprends, quand je marche. Parce que j’apprends quand je marche. Parce que je pense quand je marche. “ Le Figaro, September 12, 2023
I must walk, because I understand when I walk. Because I learn when I walk. Because I think when I walk.
I look askance at the bicyclists and joggers who pass me every day on my walk.
“Riding a bicycle is so mechanically efficient”, think I, as I wave a “good morning” to a passing rider. It’s a waste of effort if you a doing it for exercise. (I will not comment on the electric bikers who zoom past..always pedaling furiously, thinking observers will not know they are only “fake” bike riders.)
“ Bike riding is a great way to generate a UTI or a crushed urethra”, I murmur to myself as the next bike rider person passes by all decked out in ergonomic gloves, shiny aerodynamic shaped helmet, tinted bicycle eyewear, and skin tight low friction polyester riding pants—which show too many bulges.
Soon I hear the “clump”, “clump”, “clump” of a jogger coming up from behind me. This passer by gets a similar mental take down.
“Pounding the hard pavement like that can not be good for your legs, knees, or those cartilaginous cushions between those spinal vertebrae of yours” I whisper, again keeping these thoughts to myself.
These are ideas which came to mind as I walk. But then too, I thought of our ancient predecessors 200,000 years ago who perambulated everywhere. Humans walked out of the Horn of Africa, north and into Eurasia. Some turned west to populate Europe, others continued east—skirting north of the Himalayas and through the steppes of eastern Europe and into the far east, eventually, crossing the Bering Strait Land Bridge into Alaska and into North America. They continued on down through North America —crossing the narrow forested land strip into South America and onward south to the icy continental tip near Tierra del Fuego. If humans started in the Horn of Africa the overall distance (with no side trips) encompassed a trip of about 20,000 miles. Nomads walking only 10 miles per day could make such a voyage in only 5.5 years. So the whole human voyage from Africa into the entire world may not have taken even many hundreds of years. With certainty by about 60,000 years ago humans were probably on almost every continent. Perhaps a little longer for Australia and Easter Island. Here and there they may have boarded rafts to cross onto island archipelagos eventually peopling almost all of the continents, even isolated Australia. It is walking that for which we humans are so well adapted.
And thank God for trees! For trees played an essential role in our human history. Primitive fern like trees first appear on Earth way back in the Paleozoic, during the Mid Devonian Period about 385 million years ago. If it weren't for these majestic plants we would not be here—or at least not in our present form. After more than 300 million years of growth and evolution, modern flowering trees spread over every continent to form vast forests. Forests created new ecologic niches for animals to adapt to. And it was in the shade-dappled canopy-above-ground, safe from terrestrial predators, an environment where food in the form of nuts and fruits were plentiful (and there was little competition) where a group of animals known as primates first appear arose some 50 million years ago during the Eocene Epoch.
These first primitive primates, are the group of animals from which we all descend. Its a good thing too. Adaptation for climbing and living in trees generated some useful physical characteristics, such as: having one’s eyes in the front of the head for stereoscopic vision (to accurately see the distance to an escape tree branch), and having fore legs attached to a shoulder-joint which permitted wide angle of rotation (and enabled it owner to embrace a tree trunk ), and perhaps most important of all..forepaws adapted to grasping (with a separated thumb, to hold onto smaller tree limbs)—and hang on for dear life. These arboreal or tree living adaptations for climbing around in trees remained permanently with the primate clan. Even as the the African climate changed (Yes we had “climate change” even way back then) and forests to which the primates were so well adapted began to disappear.
When climatic changes cause a decrease in rainfall below about 30 inches per year forests can not be sustained. In these climatic zones grasslands with scattered trees may take over from actual forests. Such bio-zones are called “savannas”. As African forests responded and to increasing seasonal droughts and less rainfall, forest trees tended to die out and become more scattered. Grasslands grew up in the the open areas. Limited access to extensive or continuous tree cover reduced food access of arboreal primates. To exploit adequate areas for food it became necessary for these primates to descend to the ground.
Many of the arboreal primates living in these dehydrating forests died out with the trees they lived in, but others adapted to the new conditions by coming down from the trees to adapt to a terrestrial life—by “taking up bipedalism”. In this new environment, the grasping hand with the separated thumb of the primate, the primate mobile shoulder joint and stereoscopic vision were useful pre-adaptations. Bipedal primates forced to adapt to this new environment perhaps used these physical attributes to exploit this new environment. The upright posture as well as their stereoscopic vision may have permitted more effective warning concerning predators, as well as useful information regarding potential food sources. Ability to walk over long distances increased the likelihood of encountering food sources. The grasping thumb provided a means of altering and manipulating the environment to better access food sources. These may have been nuts and berries difficult to extract, as well as nutrient sources buried below ground, or under rocks. Eventually, the use of simple stone “tools” such as “hammerstones” were used to break open nuts and seeds and exploit the nutrients in the marrow of long bones of abandoned kill sites.
The first primates to climb down from the trees and take up bipedalism (walking) in Africa, appear to have done so nearly 7 million years. According to recent analysis of fossils from Africa, one of the earliest may have been Sahelanthropus tchadensis (See: Post cranial evidence etc, Daver, Guy Clarisse, Nature: 609, 94-199, 2022 ). Thus walking may be a 7 million year old practice, beating out other forms of human locomotion by many millions of years.
So humans, or at least the genus “Homo” in Homo habilis (“Handy man”) evolved from earlier bipedal primates a bit more than 2 million years ago (and died out about 1.4 MYA) . Another even closer relative Homo neanderthalis arose some 400,000 years ago and became extinct around 40,000 years ago. While our own species of great ape, Homo sapiens arose some 200,000 years ago and has lived on to the present. This one species now dominates the Earth with over 8 billion individual members.
The adaptations for life in trees permitted the primate species to walk, eventually, very effectively, but the human body is not well adapted to running. With a body originally adapted for tree living we have done quite well, with an arboreal skeleton, unsuitable flat feet, only two legs, and an awkward, upright, clumsy mode of running. For animals well adapted to running look at the adaptations of a chetah, wolf, leopard, all of whom have four legs, powerful thrusting “hip” muscles, a horizontal flexible spine for thrust, and can run with little friction and great ability to absorb the vibrations and shock from striking the hard earth—by running their toes . We are second class runners all hands down. So don’t ever attempt to outrun a four-footed animal..even a lumbering Black Bear.
We do have adaptations for walking fast, and for walking for long distances. They are our very effective cooling system—our skin. Humans evolved in a dry savanna climate and as a result developed an excellent system to cool the body. We have millions of sweat glands in our skin. each of these glands pumps water (and nitrogenous waste) onto the skin surface where it evaporates into the air. Evaporation requires heat. Each thimble-full of water (about a gram or one cubic centimeter) requires nearly 540 calories of heat to change it to a gas or evaporate it. That heat is absorbed from the human skin surface, cooling the skin and the blood with which it is supplied. As long as our bodies can evaporate the water on the surface of our bodies into the air— we cool our blood very effectively…better than most mammals.
However, in humid climates, the air is often saturated with water (relative humidity close to 100%). In these circumstances evaporation is reduced or completely retarded, very little or no evaporation occurs and our bodies heat up. Of course water (sweat) accumulates on the skin surface. A hand fan can cool the body by blowing some saturated air away from the body…but its use is limited. Too cool effectively we need dry air! Most fast running mammals have no sweat glands are though they are much faster runners…in desert and savanna climates humans can continue to pursue them..but eventually the prey mammals overheat and slow down. Thus ancient humans and modern desert hunters such as the Kung could effectively chase down antelope and other ungulates which they have targeted.
So for these reasons I proudly walk, understand, learn and think—not like those other speedsters racing by!
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