Mad Scientists: Zach Throckmorton on evolution, our feet, and what it means to be human
Post by Christie Taylor on 9/6/2012 3:00pm
Mad Scientists is a new regular feature, presenting local science researchers. We’ll talk to them about their research, why it’s interesting, and why you should care.
In July, we spoke with nanoparticle chemist Lee Bishop. For our second post, we talked to Zach Throckmorton, a PhD candidate working in the UW-Madison Department of Anthropology with professor and prolific science blogger John Hawks. Zach’s research involves feet. Thousands of them. More specifically, he looks at thousands of x-rays, measures angles and other aspects of their anatomy, and analyzes the patterns of variation he finds. Why? Because, he says, learning these patterns will help inform healthcare decisions and tell us more about the evolution of the foot, one of the structures that is distinctly human about our bodies.
D101: I'm guessing you get this question a lot, but first of all--why feet?
Zach: I became interested in studying human evolution in general because I like to people watch. Darwin wrote about "endless forms most beautiful"--I wouldn't call all human forms beautiful but they're certainly interesting! I'm interested in the foot specifically because it is a complex anatomical structure that is very important to human locomotion--obligate upright terrestrial bipedality, or walking upright on two legs as the only option--which is very unusual in animals. Western thought has a long history of being influenced by Plato's concept of the eidos - that there is a perfect 'form' for everything, including living things. Deviations from these ideal forms are considered aberrant, less beautiful, or in the context of medicine, pathological. We now know thanks to folks like Darwin that there are no perfect forms for living things. There is instead variation. And this variation, in a population of living things, usually takes the shape of a bell curve.
D101: What does variation in foot shape have to do with health care? What decisions might your research affect?
Zach: Surprisingly, medical science has not or is only recently beginning to describe normal variation for many important aspects of human anatomy and physiology. For some details of human biology, we don't really even know what is normal and what is truly unhealthy. A great example of this close to my research is the American military's policy to reject recruits with flat feet. Until recently, scientists and physicians believed the 'ideal' form of the human foot had a proud and mighty arch from the toes to the heel. My research has confirmed that not only are flat feet not necessarily a problem, but that our ancient ancestors who lived millions of years ago, have sometimes had flat feet.
My research demonstrates that when you look at enough people from both today and prehistory, there are a lot of ways to have a fully functional, healthy foot. I hope this understanding will help inform decisions about footwear, exercise activities, and medical treatment. There are a lot of foot fads, from barefoot running to those five-finger 'shoes,' and many of these fads can be really bad for your health.
D101: I didn't know foot structure was that unusual for humans--aren't ape feet pretty similar? What's so unique about human feet?
Zach: Human feet are actually strikingly different from the feet of any other animal, including our close relatives, the chimps, gorillas, orangs, and gibbons. When I give lab practical exams to my students, I put a human foot next to the feet of the apes and ask them to ID the human. They never get that one wrong. Our feet are so distinguished because of many details. For example, the heel bone (calcaneus) is huge and wide, the toes are short and the big toe in particular is very thick, the toes are capable of bending up (dorsiflexion) and not just down (plantarflexion). The whole thing looks like it's built to bear weight rather than grab things. Because that's what our feet do--they support our body weight.
D101: Okay, that actually makes a lot of sense. In that case, where are you finding variation?
Zach: Our feet vary in many regards. Some peoples' longest toe is the big toe, for others it's the second toe. Very rarely it's the third (maybe 1 in 1,000). This detail seems clinically insignificant but it's been referenced by evolutionary anthropologists as an important marker of species differences (a position I stridently disagree with, because I've seen enough living human feet to know how this character varies). The arch is another highly variable character. Some people do have very high arches, while others have no arch at all. The arch is very relevant in a clinical setting; people with both high and no arches can have trouble finding appropriate footwear, and suffer pain and discomfort from wearing shoes that were designed for other people's arches.
D101: So what does this mean for our evolution?
Zach: The most important conclusion I've reached from spending so much time looking at the foot skeletons and foot x-rays is simple: there are a lot of ways to make the human foot work. This is a surprising result because the leading ideas in my field and in medicine are essentially that the human foot has evolved to make us more efficient walkers and runners. I don't think so. I don't see one evolutionary pressure (increased locomotor efficiency) shaping every aspect of the human foot towards that one goal. I see many different anatomical details, each of which is highly variable, and that there don't seem to be many correlations that aren't easily ascribed to biomechanics. And we see this variation all the way from Lucy to today. This maintenance of variation for each character for such long periods of time is textbook balancing selection (in which multiple variations remain in a population at rates higher than can be explained by mutation)--not directional selection (in which the frequency of a particular trait shifts in one direction over time). I'm not entirely certain why the components of the human foot are subject to balancing selection, but if I were to bet on it, $1 says it's so that our feet are more resistant to catastrophic injury.
D101: What's the most interesting/exciting part of this for you? Why is it your favorite project?
Zach: As I said I like to people watch. I think the ways in which we differ from each other are fascinating, and I like to understand and think about why we're all different. I'm glad that my abstract search for evolutionary understanding also has real-world applications, like how to find shoes that fit best and avoiding unnecessary surgery. It's also a treat to be able to use my expertise in foot evolution to talk about Bigfoot, because Bigfoot is such an amazing topic to illustrate what anthropologists do. (Seriously.)
D101: Hold on a second. Bigfoot?
Zach: I use Bigfoot as a context for discussing the nature of science, and the line between science and pseudoscience. If Bigfoot is real, it's a great ape like chimps, gorillas, and orangutans, it came to the New World over Beringia like Native Americans, and it's bipedal like humans. Most of the evidence for Bigfoot's existence is of course footprints, so that's an opportunity for me to talk about my expertise in human and ape feet. I'm also working with a friend who is a PhD candidate in cultural anthropology here at UW-Madison on a book on the cultural and biological anthropology of Bigfoot, though it's not the highest priority for either of us.
D101: What's misunderstood about your area of research? Weird about it? Something ordinary citizens might not know about their own feet?
Zach: Well, when I tell people I stare at x-rays of feet and skeletal feet for 10-12 hours per day, they think I'm what's weird about my research, haha! I have seen some truly bizarre anatomies, like folks with six and even seven toes, people with too many bones in their toes so their toes are really long, things like that. As far as misunderstandings about my research, the most annoying one is that people often ask me if I have a foot fetish (I don't). Other than that, most people simply remark that they've never really thought much about their feet. So rather than misunderstandings, I think there's just near total ignorance on the topic. People tend to not pay their feet any attention until they're a source of pain or discomfort.
One piece of information I like to share with my students is an observation about what it means to be human. Anthropologists, regardless of our specific studies, ask what it means to be human. Other animals make tools, other animals have language, other animals build homes, other animals laugh when you tickle their feet (look up 'gorilla tickle'). But when you stand on your tip-toes, you're doing something no other animal can do: dorsiflexing at the metatarsophalangeal joint. Apparently, that's what it means to be human.
D101: Dorsiflexing. That's awesome. Anything else that seems important to note?
Zach: Don't run barefoot! There are two main issues with barefoot running. The first is that no matter how thick your callouses might be, they're not as protective as the sole of a shoe. If you damage a ligament or tendon, you can permanently cripple yourself. Running barefoot also makes you susceptible to picking up gross parasites like hookworm and dracunculus. The second issue is biomechanical. Barefoot running tends to promote what's called 'midfoot striking,' where the midfoot hits the ground first instead of the heel. Midfoot striking is better/more natural for some people, but not everyone. People vary in how they run comfortably/naturally. If you are a natural heel striker (most people are), then it's a bad idea to force yourself into becoming a midfoot striker because your foot isn't used to barefoot running. It's a misconception that barefoot running is more 'natural' - we know from the archeological record that people have been wearing shoes (at least soft-soled sandal type shoes) for minimally the last 40,000 years.
Throckmorton recently published a paper about the Lucy skeleton, concluding that her ankle morphology indicates she had flat feet--an example of the variation present in the Australopithecus genus of early hominids, in whom other studies have found distinct arches.
Are you a Madison-area researcher? Do you want to talk to us about it? Or do you know someone else who might? Drop us a line at firstname.lastname@example.org
Christie Taylor (@ctaylsaurus) covers science, environment, and, depending on the season, state politics for dane101. She verbs a lot of nouns, including rollerskates, radio, and Kurt Vonnegut. A Madison native, she's not sure she'll ever quite manage to leave Wisconsin, and that's just fine by her. Contact her at email@example.com.