Two-Legged Walking and Human Skull Traits Evolved in Tandem

Fossilized skulls suggest that bipedalism and human evolution go hand-in-hand.

Posted Mar 17, 2017

Wikimedia/Creative Commons
The 2.8 million-year-old Australopithecus africanus "Taung child" skull was discovered in South Africa in 1925.
Source: Wikimedia/Creative Commons

New research further validates that bipedalism (walking upright on two feet) evolved in concert with unique features of the human skull. The latest paper on the anthropologic significance of two-legged walking, "Another Look at the Foramen Magnum in Bipedal Mammals," was published March 17 in the Journal of Human Evolution.

Walking upright on two legs makes humans unique and distinguishes the earliest hominids from other apes. In fact, two-legged upright walking is one of the most prominent characteristics that depicts our hominid lineage.  

Interestingly, until the early-20th century, most anthropologists believed that our "big brains" made hominids unique. However, this system of belief began to shift in the 1920s when South African anthropologist, Raymond Dart, discovered a very small fossilized hominid skull from almost 3 million years ago, referred to as the “Taung Child."

Although the Taung Child had a small skull and brain, one feature stood out to Dart as being human-like; the foramen magnum (the hole at the base of the skull which the spinal cord passes through) had a relatively forward position towards the front of Taung's skull. This foramen magnum position (FMP) indicated that Taung held its head erect and walked upright on two legs. The foramen magnum of other apes—who do not walk upright on two legs—is positioned further towards the back of the skull.

That being said, Dart's 1925 hypothesis about the link between FMP, bipedalism, and human evolution was surprisingly controversial. For almost a century, paleoanthropologists have continued to debate whether the evolution of bipedalism required the foramen magnum to be shifted forward so that the head could balance directly atop the spinal column in an upright position while walking.

In an attempt to appease the foramen magnum evolutionary skeptics, two anthropologists—Gabrielle Russo of Stony Brook University and Chris Kirk of the University of Texas at Austin—conducted the aforementioned research on bipedalism and the human skull published today. Their latest research is a follow-up to an earlier study, "Foramen Magnum Position in Bipedal Mammals," the duo published a few years ago in the Journal of Human Evolution.

Russo and Kirk's earlier research identified that a forward-shifted foramen magnum is found in skull fossils of other bipedal mammals. For their latest study, they used new methods to quantify aspects of foramen magnum anatomy and sampled the largest number of mammal species for this type of study to date. In a recent statement to UT Austin, Kirk said:

"This question of how bipedalism influences skull anatomy keeps coming up partly because it's difficult to test the various hypotheses if you only focus on primates. However, when you look at the full range of diversity across mammals, the evidence is compelling that bipedalism and a forward-shifted foramen magnum go hand-in-hand.

We've now shown that the foramen magnum is forward-shifted across multiple bipedal mammalian clades using multiple metrics from the skull, which I think is convincing evidence that we're capturing a real phenomenon . . . Other researchers should feel confident in making use of our data to interpret the human fossil record."

Another major part of Kirk's anthropology research on bipedal locomotion focuses on the evolution of primate sensory systems. For example, in addition to upright walking, primate evolution also involved a major reorganization of the visual system. This included larger eyes, convergent optic axes, a broader field of binocular vision, and the parallel evolution of trichromatic color vision. 

Kirk's research on vision and bipedalism dovetails with a February 2017 study by researchers at the University of California, Santa Barbara who reported that low-intensity aerobic exercise (such as walking) arouses neurons in the visual cortex that enhance human vision. This paper, "Acute Exercise Modulates Feature-Selective Responses in Human Cortex," was published in the Journal of Cognitive Neuroscience

Other recent studies have found that the link between walking, sensory systems, and creative capacity may be intertwined. As an example, in 2014, Marily Oppezzo and Daniel Schwartz of Stanford University published a study, "Give Your Ideas Some Legs: The Positive Effect of Walking on Creative Thinking," which reported that going for a walk led to more creativity than sitting. 

Along these lines, the Museum of Walking (MoW) is an educational resource center committed to the advancement of walking as an art practice. MoW curates grassroots events that utilize the everyday act of walking to tap into sensory systems that have evolved over millennia and appear to boost creative capacity.

MoW founder, Angela Ellsworth, says, "Making art is one way of listening to the world, walking is another." On March 18, MoW is holding "theWALK" to promote meaningful community engagement, public health, and sustainability awareness while enhancing creative and divergent thinking.

In a digital era that is marked by an epidemic of increased sitting and less walking, hopefully, the latest research on the evolutionary importance of bipedalism—and the paramount role that walking upright on two legs played in becoming human—will motivate you to use walking as an easily accessible way to stimulate sensory systems, arouse neurons in your visual cortex, and get your creative juices going. 


Gabrielle A. Russo, E. Christopher Kirk. Another look at the foramen magnum in bipedal mammals. Journal of Human Evolution, 2017; 105: 24 DOI: 10.1016/j.jhevol.2017.01.018

Gabrielle A. Russo, E. Christopher Kirk. Foramen magnum position in bipedal mammals. Journal of Human Evolution, 2013; DOI: 10.1016/j.jhevol.2013.07.007

Tom Bullock, James C. Elliott, John T. Serences, Barry Giesbrecht. Acute Exercise Modulates Feature-selective Responses in Human Cortex. Journal of Cognitive Neuroscience, 2016; 1 DOI: 10.1162/jocn_a_01082

Marily Oppezzo, Daniel L. Schwartz. Give your ideas some legs: The positive effect of walking on creative thinking. Journal of Experimental Psychology: Learning, Memory, and Cognition, 2014; DOI: 10.1037/a0036577

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