Verticality, Part III: Inception

Our first act of descension and our first act of ascension

This chapter is part of a series that compose the main verticality narrative. The full series is located here.

Our species evolved within the context described in the first chapter, and our physical surroundings would provide the foundation for our struggles with verticality, as described in the second chapter. These early struggles would be defined by two acts. The first is an act of descension: we came down from the trees and out onto the savannah to become surface-dwellers. We would still carry much of the baggage from tree-dwelling life with us, however. I’ll henceforth refer to this baggage as our source-code. The second is the shift to bipedalism, resulting in our upright, vertical bodies. Together, these two acts would set the stage for the future and our never ending struggle to escape the earth’s surface.

Before we jump into each of these acts, however, a few words on the difficulties of understanding our evolutionary history are warranted. When discussing the human story and our origins, it’s important to keep in mind that we are still working to understand each. In fact, we may never get the entire story because so much of it has been lost to time. Think of it like a puzzle without borders. We’re slowly finding pieces to this puzzle, one by one. Some pieces fit with existing pieces, and some don’t. Those that don’t fit may change other parts of the puzzle that we thought fit well together. Many pieces have been permanently lost, and some we may never find. This makes it terribly difficult to be sure about any of our theories and ideas about how we got here.

Left: Pedigree of Man by Ernst Haeckel from 1897. Right: Genealogical Tree of Animal Life by Benjamin C. Gruenberg from 1919. Though intriguing images, each reinforces many misconceptions about the process of evolution and equates evolution to forward progress, with Man at the top. [1]

One common misconception of evolutionary history is that it functions like the branches of a tree, with a clear path from root to leaf. Ernst Haeckel’s Pedigree of Man from 1897 and Benjamin Gruenberg’s Genealogical Tree of Animal Life from 1919 are perfect examples. Each illustrates a clean, linear path with simple branches for each species and a vertical progression from simple to complex lifeforms. The actual evolutionary story is not a tidy, linear progression, as each drawing shows. It is an impossibly complex, messy, tangled web of competition, failed mutations and death that slowly changes life on earth over time. This reality is nearly impossible to show in a graphic like those shown here, so we must deal with some level of simplification and abstraction in order to understand it.

Another common misconception is that evolution equals progress, or that the evolutionary tree follows some sort of linear narrative through time, with more complex life forms at the top. In each drawing above the simplest life forms are shown only at the base of the tree, when in reality many of these species still exist and thrive alongside us today. Evolution does not equate to progress, because that would suggest there is a conscious effort somewhere to make life better or more complex over time. Evolution is an imperfect, blind process that simply molds and shapes life over time based on survival fitness.

Hannah Devlin, in a Guardian article from 2018 sums up the reality of the evolutionary story: ‘different branches evolve at different rates; new traits can emerge several times independently; splits can be dragged out over millennia and across continents, with populations diverging and then interbreeding again. Rather than the tree of life it’s more like a dense, thorny bush.’ She goes on to explain that in order to understand the human story, the best we can do is observe the current state of life on earth, work backwards through the evidence we’ve found so far and react to new evidence as we find it.[2]

This messy, dense and thorny bush is where we’ll venture into next. The theories and reasons for how and why any of these events happened are still being debated, and will most likely continue to be for some time. How did one species of primate come to colonize the globe, and how has our innate need for Verticality contributed to this story? There are few straightforward answers as of yet, but we can get a basic picture of it by analyzing what we do know so far.

Source Code

Our story begins with our ancestors who lived up in the trees. Their lifestyle was based on verticality; height equaled safety, since most predators were on the surface, and food was located up in the canopy. Height also equaled death in the case of a fall. This presented a paradox: height was something to seek out for safety but also something to avoid because of its dangers. It was our original love/hate relationship. Our ancestors were well-suited to deal with these dangers, however. Through millions of years of evolution, they had developed manipulating limbs for climbing and grasping, as well as eyes that both face the same direction, giving them three-dimensional vision and depth perception.[3]

Despite the adaptation to arboreal life, change was in the air. Our ancestors would begin to split off from their hominid relatives by descending from the trees and moving out onto the savannah. This was most likely because the forests were shrinking in size sometime around 15 million years ago. This split would have profound effects on the hominid family. Those who stayed in the trees would evolve into the chimpanzees, gorillas, orangutans and gibbons that we see today. Those who left the trees in favor of a surface-based life would evolve into modern humans.[4] This was our first major evolutionary act tied to verticality. We were now surface-dwellers.

Lewis Hine’s Icarus from his Empire State Building photograph series from 1930-31. A fear of heights is innate in us, but some of us don’t suffer from it at all, which makes jobs like this possible. [5]

Once we descended from the trees to the savannah, we still had to deal with the psychological baggage of arboreal life. Our brains still carry much of this baggage, and we’re still learning just how deep these connections go. One example of this is a fear of heights.[6] This phobia is common in our species, and is innate for those who suffer from it.[7] It runs so deep in us that it’s been estimated to have developed in the Mesozoic era, roughly 140 million years ago. A complete absence of this fear is a genetic trait that runs in families.[8] Take the above photo for example. It’s from Lewis Hine’s Empire State Building photograph series from 1930-31. The series shows construction workers seemingly unaffected by the dizzying heights of their job. They all carry the genetic trait that prevents them from having a fear of heights. For anyone with this fear, it’s hard to imagine how these men can be so calm when confronted by such a visceral danger of falling. A second example is our sensitivity to tiny vibrations from our environment. This has been studied in high-rise buildings, where movement and vibration can cause motion sickness and fear among building occupants. This could be psychological baggage from our primate ancestors, for whom slight vibrations of a tree branch could signal the approach of a predator, so fear would be a proper reaction to this stimulus.[9]

Another example is a child’s proclivity for climbing trees and building tree forts. I can remember loving both activities as a boy, even though I had a crippling fear of heights. The paradox mentioned above was all too real for me; when climbing, higher was better, but it also meant more danger, and there was always a point when I could go no higher. Once up in the fort, there was a sense of safety and security from being up off the surface. When descending, it was always tricky because my focus was on looking down and the danger of a fall. Still, I had a great sense of achievement after climbing a tree or building a tree fort, much like the mountain-climbing examples discussed in the previous chapter.

Bipedalism

Concurrent with our ancestors’ descension from the trees, we also developed bipedalism, or the ability to walk upright on two legs. There are various theories for when and why this happened, and the answer probably lies in some combination of all of them.[10] What’s important to keep in mind here is the shift to bipedalism likely began while we still lived in the trees, and we made the full transition once we had descended onto the savannah.[11] This makes sense because bipedalism has benefits both for arboreal life and surface life, but it also puts costs on our bodies, some of which we’re still dealing with today.

Rudolph Zallinger’s iconic March of Progress from 1965. This image suffers from the same criticism of the Tree of Life drawings shown above. Evolution is not a linear process, nor does it equate to forward progress. I show it because it’s familiar and it does a good job of conveying the progression over time that resulted in our upright, bipedal posture. [12]

There are many potential benefits from the shift to bipedalism. First, it freed up our forelimbs to perform other tasks, such as tool-making, carrying our young, foraging, threat displays and sexual selection.[13] Second, once we were on the savannah, standing upright made us taller and raised our heads, which made it easier for us to see enemies, predators and game.[14] As a result, taller individuals had higher survival fitness; they could see predators earlier, could reach higher branches, etc. This benefit still affects sexual selection today: height in human males is generally seen as a positive attribute by females when choosing mates. Another possible benefit is that our erect posture moved our head to the top of our bodies, which helps cool down our brain.[15] This could’ve paved the way for the rapid growth of our brains during the Cognitive Revolution, but we’ll get to that in the next section.

Once we took advantage of bipedalism, we also had to adapt to the new costs it put on our bodies. The act of standing upright and balancing on two feet changed the structural requirements for many parts of our body. Before we became bipedal, we had four limbs to support and balance our entire body weight. Once we began walking upright, our two legs had to support and balance that same body weight. Over time, this resulted in bone enlargements in our heel, knees, leg length and hip joints to cope with the extra weight to bear. Balance was also a major factor. Our knees and our spine both shifted to align with our center of gravity. Each of our knees moved inward in order to put them directly under the body’s center of gravity. The lumbar and thoracic curves of the spine developed in order to align our spine with our body’s center of gravity, directly over our feet.[16] These changes occurred slowly over millions of years, and we’re still not completely adapted to our bipedal ways. Lower back pain is a common occurrence for humans today, because our lower backs are required to support much more weight than before we became bipedal. All this effort and change underlines the profound advantages bipedalism had for our ancestors. After all, we wouldn’t have become bipedal if it didn’t give us a higher survival fitness compared to our competitors.

Eadweard Muybridge’s Running At Full Speed from 1872. Once we became bipedal, we were a vertical species.

The shift to bipedalism represented our first major defiance of gravity, and set us apart from nearly all other surface-dwelling creatures, including our closest relatives. We were now a vertical species, carrying the baggage of a vertical past in the trees, and our lives would be defined by ascension. As we grow, we are constantly ascending. We begin in the womb, which is closely related to caves and the underground, as discussed previously. In birth, we exit the womb into the light, and begin life on the surface. As adolescents, we progress from crawling to standing, and we grow taller as we get older. Our vertical bodies become our own axis-mundi, which gives us a deep connection to mountains and trees. Furthermore, our bodies also contain an inherent vertical hierarchy: our most precious cargo (the brain) and most of our sensory inputs are located in our head, which is the highest point of our bodies, lifted up as far as possible from the ground.

The combination of our source-code and the shift to bipedalism meant our lives thereafter would be defined by verticality. Our ancestors had become a vertical species, but they were still under-qualified for survival on the savannah. They were smaller and weaker than other predators and prey, so they would need to find ways to out-compete all these competitors in order to rule the savannah. In the next chapter, we’ll take a look at a few of the developments that allowed our ancestors to escape the food chain and populate the entire globe.

Keep reading: Verticality, Part IV: Beating the System

[1]: Haeckel, Ernst. “Pedigree of Man.” The Evolution of Man, Vol. II. 1879.; Grunenberg, Benjamin C.. The Story of Evolution. Norwood: Plimpton Press, 1929. 71.

[2]: Devlin, Hannah. "Tracing the tangled tracks of humankind’s evolutionary journey." The Guardian, February 12, 2018.

[3]: Morris, Desmond. The Naked Ape: A Zoologist's Study of the Human Animal. New York: McGraw-Hill Book Company, 1967. 18-19.

[4]: ibid.

[5]: Hine, Lewis. “Icarus atop Empire State Building.” Empire State Series. 1930-31.

[6]: A fear of heights and a fear of falling are two distinct, but related fears. For simplicity, I’ll refer to both collectively as a fear of heights.

[7]: Pinker, Steven. The Blank Slate: The Modern Denial of Human Nature. New York, NY: Viking Penguin, 2002. 231.; Brandt, Thomas, and Doreen Huppert. "Fear of heights and visual height intolerance." Current Opinion in Neurology 27 (2017): 111-17.; Marks, I.M., and Nesse, R.M. “Fear and Fitness: An Evolutionary Analysis of Anxiety Disorders.” Ethology and Sociobiology 15. 1994. 247-261.

[8]: Bracha, H. Stefan. "Human brain evolution and the “Neuroevolutionary Time-depth Principle:” Implications for the Reclassification of fear-circuitry-related traits in DSM-V and for studying resilience to warzone-related posttraumatic stress disorder." Progress In Neuro-Psychopharmacology & Biological Psychiatry 30 (2006): 827-53. 835.

[9]: Knapton, Sarah. "Wobbly skyscrapers may trigger motion-sickness and depression, warn experts." The Telegraph, March 19, 2017.

[10]: Vaughan, Christopher L. "Theories of bipedal walking: an odyssey." Journal of Biomechanics 36, no. 4 (April 2003): 513-23.

[11]: Ko, Kwang Hyun. "Origins of Bipedalism." Brazilian Archives of Biology and Technology 58, no. 6 (Nov. & dec. 2015): 929-34. 933.

[12]: Zallinger, Rudolph. "The March of Progress." In Early Man, 41.45. New York: Time-Life Books, 1965.

[13]: Ko, 929

[14]: Harari, Yuval Noah. Sapiens: A Brief History of Humankind. New York: HarperCollins Publishers, 2015. 9.

[15]: Oppenheimer, Stephen. Out of Eden: The Peopling of the World. London: Constable, 2003. 4-7.

[16]: For a thorough overview of the human body’s evolution, see: Aiello, Leslie and Christopher Dean. An Introduction to Human Evolutionary Anatomy. Oxford: Elsevier Academic Press, 2002.