Barefooting Part 1 – Were we really born to run … barefoot?

The book Born To Run, by Christopher McDougall, has had an immense impact on the running world and beyond. The hardcover was on the best seller list for most of 2010, the paperback for much of 2011, and there’s a movie in the works. It is largely responsible for the boom in barefoot running and minimal shoes. It has spawned great interest in ultra running, especially the Leadville 100 (the 2011 race sold out months earlier than ever before).

While I highly recommend the book – it’s entertaining, informative, and inspiring – I’m skeptical about barefoot running. I think it’s good that this has gotten runners to think about their form (I’ve been teaching running form since 2003, using the same principles found in Chi, Pose and almost every other running form system and minimalist). Despite the evangelical zeal of barefoot runners, it’s not the magical cure for all running injuries and running shoes are not evil; the science doesn’t show either.

In part 1 I’m going to briefly review the book and critically evaluate barefoot running. In the part 2, I’ll look at ways to strengthen your feet and improve your form. This should be valuable to you whether or not you are thinking of going barefoot or minimal (I will use these terms almost interchangeably throughout), and absolutely essential if you do.

Born To Run: At its core, the book is a wonderful tale of adventure travel. Beyond the adventure, McDougall weaves in everything from the evolution of ultra running, Tarahumara history and culture, an analysis of the running shoe industry, to cultural anthropology (i.e., were we born to run?). That’s where the book hits its mark.

The adventure took place in 2006, when a group of Americans travelled down to Copper Canyon, in Mexico, for a 50 mile race with the Tarahumara. The cast of characters including 6-time Western States 100 winner Scott Jurek, a guy named Barefoot Ted, a 20-something party animal who would stay up all night drinking and then win a race the next day (subsequently, she has gotten serious and has run sub-15 for 100miles), and the author. They were travelling down to meet up with Caballo Blanco (his true name and background are revealed at the end of the book), perhaps the biggest character of them all, an American who had been living with the Tarahumara. The story of how the race came about, traveling to Copper Canyon, and the race itself is quite entertaining.

The book has one of the best histories of ultra-running, and the most detailed account I’ve read of the much heralded 1994 Leadville 100mi run battle between Ann Trason and the Tarahumara. In that race, Tarahumara runner Juan Herrera held back early on, while Ann Trason led for much of the race. When he finally let go, he flew by Ann, averaging 2 min/mi faster, to shatter the course record and win by 34 minutes. His winning time of 17:30 stood as the record for 8 years (who knows how much faster he would’ve run if he hadn’t held back). Ann Trason’s 2nd place finishing time of 18:06 is still the women’s record, over 1.5 hours faster than any other woman has run at Leadville.

Were we born to run … barefoot?

The part that created all the buzz in the running community (and beyond), and made the barefoot movement take off is the claim that we, humans, were born to run, and run barefoot. The argument combines both bio-mechanics (the heel is important for balance when standing and walking, but not necessary for running) and evolutionary biology.

The evolutionary biology theory of barefoot running (i.e., born to run) is that our ability to run long gave us an advantage over our prey. Even the fastest humans are a lot slower than four-legged animals (and we didn’t have the weapons to kill them from afar), but we could run them to death (almost literally) over time. Humans keep cool through sweating. Other animals don’t sweat. They dissipate heat through breathing. So, while they can easily out sprint us, they quickly begin to overheat, have to switch much of their breathing from energy to cooling. Quickly they slow, and if forced to continue, they overheat, and stumble and collapse, making them easy to kill.

There are several problems with the claim that since our ancestors ran barefoot successfully, we should too.

1) It’s unlikely that all of our ancestors were good runners and hunters. It’s likely that only the few good runners were the ones who hunted. In other words, we weren’t all born to run.

2) Ancient humans grew up without shoes and developed strong and tough feet. They also were physically active – climbing trees, building shelters, etc., – developing strong core and stabilizing muscles. In contrast, we sit behind a desk, in front of a TV, drive cars, etc.

3) While some of us may have been born to run, I don’t know that we were born to race, and to do so for 26 miles on pavement.

Are shoes to blame?

McDougall’s book includes a near indictment of the running shoe industry claiming that cushioned shoes enable heel striking (which leads to injury). Barefoot advocates state that injury rates haven’t changed since the introduction of cushioned and motion control running shoes – 70% in the 70s, and 70% today – and that if shoes were better, they would have declined. However, there are several problems with this argument. And, there’s no scientific evidence that shoes either hurt or help runners.

Before the first running boom, when shoes were strips of thin rubber attached to a leather upper, most runners were built like me (I did my first race in 1971) – wispy, thin, efficient (i.e., born to run). As the number of runners has grown immensely, so has the variety of body types. On average, runners today or slower (and probably heavier) than before the modern running shoe – median marathon times in 1980 were 3:32 for men and 4:03 for women; in 2008 they were 4:16 & 4:43. A lot of newer runners may not have been born to run. In fact, cushioned and control shoes may be preventing them from getting more injured, and may have been necessary to enable them to get into and continue running.

Even with efficient runners, it could be that modern shoes have allowed runners to train more and harder before they become injured. In other words, injury rates may remain a constant regardless of whether or what kind or shoes runners wear, because runners will tend to push themselves in training to the point they get injured.

Rather, the problem with shoes may be that it restricts your foot from functioning naturally. Your foot is supposed to pronate, the arch collapse, toes splay out, flex at the mid-foot. This is all part of dissipating some of the impact, and gathering energy in a spring-like fashion to return to your push off. If you wear shoes that restrict those motions, you don’t allow the muscles to strengthen and learn to operate efficiently.

Even for those who have an efficient stride in shorter runs/races, it’s not clear that’s sustainable over a longer race (i.e., ½-marathon and longer). High speed video analysis of runners towards the latter half of longer races show that even the majority of elite runners land on their heels (although, I’m not sure whether such analysis is really able to distinguish between where it appears the foot strikes and where the major impact is). So, as your foot fatigues, you may need some heel cushioning. And, cushioning may forestall the fatigue that, among other things, makes you more susceptible to injury.

I don’t have much to say about zero and low heel drop shoes because they are so new onto the market, and there hasn’t been time to study them. I read one report that implied that the amount of heel cushioning didn’t matter, but whether there was cushioning or not did. However, that was a very small and not very scientific study.

Is forefoot better?

The science does not show that barefoot running or forefoot (for purposes here, I use forefoot and midfoot interchangeably) striking reduces injury. Harvard evolutionary biologists Daniel E. Lieberman, who’s work is widely cited in the book and by barefoot advocates, states on his website, “Please note that we present no data on how people should run, whether shoes cause some injuries, or whether barefoot running causes other kinds of injuries. We believe there is a strong need for controlled, prospective studies on these issues.”

Dr. Lieberman’s most widely cited study shows how loading rates are significantly higher with heel strikers vs. forefoot strikers. There are several problems with this analysis. Force exerted down onto a strike plate doesn’t equate to force transferred up through a cushioned shoe. More loading doesn’t necessarily mean excessive; no one has showed how much is too much. Loading rates, rather than indicating excessive stress on the body, may simply indicate inefficiency. In fact, there’s a theory that the higher loading stresses the bones, making them stronger. Also, it’s not been shown that such measures in a lab represent what’s happening in the real world.

Another theory says that your body adapts to the stresses it encounters and automatically adjusts your stride (you automatically adjust your stride when you change from concrete, to dirt, to mud or sand). In other words, if heel striking hurt, you wouldn’t.

It’s not clear that forefoot striking reduces injuries. For one, landing off your heels means your muscles absorb more of the impact. Those who don’t take the time to properly adapt to fore/midfoot striking are prone to more soft tissue injuries. Even after properly adapting, on longer runs and races, muscles fatigue (bones don’t), becoming less efficient, less able to stabilize and support, which can lead to greater injury. Other studies have shown that higher frequency (hertz) forces, associated with heel striking, travel through bones, while lower frequency forces, associated with forefoot striking, travel through the muscles. So, changing to mid/forefoot striking may be trading off one set of injuries for another.

More than forefoot

Forefoot striking alone is not sufficient, and may not even be necessary for an efficient stride. For example, the University of Virginia’s Center For Endurance Sport has done analyses that indicate that where your foot lands relative to your body – your foot should land under the center of gravity (COG) – is more important. While they say that most people who land under their COG do strike forefoot, they can show you heel strikers who land under their COG and forefoot strikers who land in front. Regardless of what part of the foot you land on or what kind of shoe you are wearing, landing under your COG produces less impact than landing in front. It’s also more efficient.

Let’s add two more important characteristics of an efficient foot strike – the direction your foot is moving, and your stride rate.

When your foot hits the ground, it should be pulling back. This “paw back” motion (like a cat scratching) means that you are using the existing inertia of your body’s forward motion over the ground (or the ground’s/treadmill’s backwards motion under you) to help propel you forward. When you land flat, or with your feet moving forward relative to the ground (sounds like sandpaper), not only is the impact greater, but you stop your forward momentum (actually slowing yourself down), and require that much more energy to generate the forward momentum. Another way of thinking of this is when you have to move a heavy object (e.g., a large box), it’s easier to move it if you get a running start. Combine the paw back with landing under your COG, and it takes less energy to produce a more powerful stride than how a lot of runners land. It’s easier to push something away from your body than pull it towards you.

A faster stride (most non-elite runners can benefit from a faster stride) is more efficient, has less impact, and leads to faster running. Stride rate is much more a factor of how much time your foot is on the ground, than how much time it’s in the air. When you land, the muscles and tendons in your foot and leg collect energy and then return it, like a spring. That return of energy can happen very quickly. The longer your foot is on the ground, the more energy is absorbed, and the less is returned to propelling you forward. A faster stride means you don’t have to propel yourself as far in the air meaning less energy and less impact.

And that’s just foot strike. Other factors to consider include pelvic tilt, arm swing, shoulders and head tilt.

Can we adapt?

Even if it turns out that barefoot and/or forefoot running is better for runners, it’s not clear how easily, or even whether we can adapt to it after a lifetime of wearing shoes. Analysis of runners at barefoot/minimalist races (done after the start when runners have settled into their stride) has shown that the majority of runners still land on their heels.

Anecdotally, having watched a lot of runners, and through my own experience, it’s not clear that it’s the cushioning that causes people to run on their heels. Rather, it may be that people have different, natural running styles, perhaps altered by lack of ankle flexion from years of little or misuse (e.g., high heeled shoes). I know runners whose heels never seem to touch the ground regardless of what kind of shoe they’re wearing, and others who can’t get off their heels. Personally, I’m able to consciously alter my foot strike in whatever kind of shoe I’m wearing. For me, at least, it’s not the shoe that dictates my foot strike, but how my muscles are conditioned to fire.

Bottom line

Before you rush out and buy a pair of barefoot shoes (contradictory terms), consider whether you need to change. If you have recurring injuries – not just in your foot, but radiating up to your hips and lower back – then you might benefit from a change. However, the irony is that those who can benefit from it the most can afford it the least. I’ve always had a fairly efficient stride and good feet, and have never worn supportive shoes. I can, and have run a few miles barefoot with no build-up. However, for those who don’t have good feet and have been wearing supportive shoes, you may only be able to run a few seconds barefoot without risking injury, and it may take months of build up before you can do any substantial barefoot running.

There is a lot of benefit in working on your running form, even for efficient and injury free runners. Athletes in every other endurance sport – e.g., cycling, swimming, x-c skiing – work on their form. Whatever the reasons, most non-elite runners don’t; they just run.  Becoming more efficient will make you faster, less likely to get injured, and less tired. You will be able to wear lighter (which should also make you faster), less supportive shoes, and thus less expensive shoes, that will last longer.

In the next part I will talk about how to strengthen your feet, how to transition to less supportive shoes, and more about who should consider going barefoot.


NY Times article 6/8/11 –

Barefoot lab at Harvard –

RW interview with biomechanics expert Benno Nigg, 1/9/11 –

Science of Sports blog on barefoot running, 6/6/11 –

UVA Center for Endurance Sports – or


13 thoughts on “Barefooting Part 1 – Were we really born to run … barefoot?

  1. I disagree with your conclusion about light weight shoes. Light weight shoes are just as expensive if not more expensive than a regular running shoe. Take a look at racing flats $80-$120. Not to mention the flimsy construction wears out ridiculously fast and they often need replacement. Track spikes are the exception $65, but who would want to wear those in a road race?

    • Not from my experience. Here’s a look at some prices.
      Asics Kayano (support) or Cirrus (cushion) $150
      DS Racer $100, Hyperspeed $80

      Saucony Hurricane (support) $140, Cortana (cushion) $145
      A5 $100, Kinvara $90

      Mizuno Nirvana (support) $140 Rider (cushion) $115
      Ronin $100, Musha $85

      Brooks Beast (support) $130, Ghost (cushion) $100
      T7Racer $85, Pure Flow $90

  2. Great piece, Adam. Useful and thought provoking. Thanks for taking the time to put it all together.

    I have several acquaintances who jumped too quickly into minimalistic shoes and barefoot running and who quickly ended up injured. I wish I could have spoken to them before they started. Who knows, your next piece might prevent similar injuries?

    Personally, I love my weekly barefoot sessions (when the snow allows!). Not just for the way I can truly feel my form improving while running fast and free and barefoot, but above all for the sheer joy of it, for how the running feels, that is: light, grounded, and above all ‘natural’.

    Clearly, barefoot running isn’t appropriate for absolutely everyone under all conditions and for all runs, but I bet most runners would benefit greatly from a few careful, considered, (and initially short), barefoot runs.

    Even if it’s just for the joy of it!

    • Rob, thanks for the link. Interesting, but far from conclusive.

      1)This is a very small study (n=52), with a group that isn’t representative of the larger running population, both in terms of demographics, and the type of running/training.

      2)People who “habitually” RFS may have other factors that make them more likely to be injured. Those same factors may be what caused them to habitually RFS. Correlation doesn’t equal causation. They mention many other factors which also lead to higher injury.

      3)If you believe what the UVA people say, it’s not FFS vs. RFS that’s important, but location relative to center of gravity (COG). There’s a high correlation between COG and RFS v. FFS – it’s hard (not impossible) to FFS if you land in front, and RFS if you land in back. Think of this in terms of physics, vector analysis. Since we’re (at least most of us) are in Colo, think of the pole plant in skiing. The force from sticking the pole in the snow in front of you (while you’re moving forward) is much greater than when it’s beside you (and it also slows you down).

      4)Confirmation bias. So much of the belief and focus amongst barefooters is on FFS vs. RFS. Thus, they go out looking for it. If you look for something specifically, or go into an analysis with a predisposed notion of what you think you might find, you are more likely to find it.

      Note one of the related citations of the study where they “observed increased frequency of rearfoot striking” later vs. earlier in a marathon.

      P.S. Unfortunately I’m not able to read the entire study. My wife, however, is a doctor and researcher. I’ll see if she can access it for me.

  3. I started running with the Vibram 5-fingers after reading “Born to Run” about two years ago, and have been doing so once in a while since. Here are my two cents:

    1. Start slow. Really slow. The book is great, but it gives the impression that we need to be liberated from shoes, and once you start barefoot running it’s like fish back to water. The reason barefoot running is not for everyone is mostly because of the tough discipline it requires when you first start. For experienced runners it would be highly frustrating, because I’m talking about starting barefoot running at time lenghts of a minute. Then rest a day. Then increase to 2 minutes. Rest a day. And so forth. Almost no one has the patience for that. Several weeks after starting running with the 5-Fingers I developed a pinched nerve in my left foot, which hurt like hell and there was nothing to do about it other than rest.
    Later I re-acclimated to barefoot running really, really slowly, and it was fine. At the height of my use of the 5-Fingers I could run ~7 miles none-stop, ON PAVEMENT. Which brings me to my next point:

    2. I was never able to run with the 5-fingers on trails, no matter how acclimated I got. Granted, I have the old version, which is really flat at the bottom, no cushioning whatsoever. At some point about a year and a half ago I had my Icarus moment: I was overconfident with my ability to run with the 5-fingers, and decided to take on Apex, which is right by my home. The way up was great. Great sensation. On the way down, no matter how slow I ran, my feet started to suffer from loose gravel and sharp rocks, until at some point I just had to stop and walk the rest of the way home. The pain afterwards was so bugging, that I couldn’t run even with regular shoes for about two months afterwards. Which brings me to the next point:

    3. Hurt is unacceptable. As runners (or athletes) we see pain as part of “no pain no gain”. But this is not the case with barefoot running. If your foot starts to hurt, stop right away. Walk the rest of the way, or pack a pair of regular running shoes in a backpack before you head out. I was a fool twice, and twice I payed for it.

    4. That being said, I still use the 5-fingers occasionally. I wear them for several-miles runs on pavement or treadmills, during sprint training, and for rope-jumping. BTW, rope-jumping barefoot is an excellent way of introducing fore-foot impact to your feet.

    5. Overall, my running was improved after starting with 5-fingers, but not because it was necessarily healthier of “better”. It did help me develop a better posture, adopt a faster, shorter stride, and fore-foot strike that I implement with regular shoes on trails. It just makes you more aware of the way you run, because if you don’t do it right you get hurt. I noticed that I tend to twist my ankle much less (I have a re-occuring thing) with fore-foot strikes – it seems that at uneven ground the foot manages to correct itself much better when I run this way. Intuitively it makes sense to me, but I can’t quite explain why. Maybe most of the impact is absorbed in the foot and not the heal. It also convinced me never to invest in expensive shoes – I run with a $50 Adidas pair and I love it.

    There is definitely something liberating and fun about running barefoot (or almost barefoot), but it is not for everyone, not for every situation, not for every terrain (BTW, I was able to run on snow. It’s cold as hell at first, but when you forefoot strike the feet really begin to sweat and warm up after a mile or so…).

    • Assaf,

      Good info and advice.

      RE $50 shoes: Phil Maffetone (used to be a triathlete coach/guru) said something similar at a clinic I attended 13 or 14 years ago. As long as the shoes are flexible and, more importantly, fit and feel good on your feet, than cheap shoes you might buy a Target, Sports Authority or a dollar store might be just as good.

      • Hi Adam,

        Unfortunately, commodities are often priced based on what the consumer is willing to pay, not based on the cost of production (e.g., mineral bottled water… How come Coca Cola, which contains water plus other things, costs less than just water?).

        Same with minimalist shoes, although it is somewhat counter-intuitive. You get less material, simpler design, yet you pay more because the manufacturer knows you are willing to pay more… 5-fingers start at $80 or so, the Merrel Glove at $100 or so.

        I enjoy reading the discussion between you and Nathan. While I believe that our pre-agricultural ancestors needed to be runners in order to be hunters, I don’t discount human ingenuity and the ability to make traps, or stalk prey. Native Americans in Colorado used to chase deer into steep, dead-end canyons (or at least that’s what the sign in 7-Falls says…). Running is definitely a plus, but I’m not sure about endurance long-distance running. Also, McDougall suggests (or quotes others) that running was a feature of the entire community, bringing the example of a modern-day runner that completed a marathon while carrying her baby. I don’t think that in this case a modern extreme equivalent necessarily points at the norms and social structures of thousands of years ago.

        But then again, maybe we lost some of these norms, and perhaps even diminished natural selection that keeps the gene pool of only the best hunters/runners, once we moved towards domestication and agriculture. In evolutionary times 10,000 years (start of the agricultural age) is a fairly short time, but natural selection happens faster than persistence of a new trait due to DNA mutational changes (and I totally can’t cite anything to support that!).

  4. Adam, thanks for your post. It is interesting, barefoot running has become an emotion subject, as you point out. I don’t think I’ve heard of anyone being “neutral” on this subject yet! Everyone has an opinion, so here’s mine 🙂

    You state: “It’s unlikely that all of our ancestors were good runners and hunters. It’s likely that only the few good runners were the ones who hunted. In other words, we weren’t all born to run.”

    I think it IS likely that the natural and sexual selection for even a handful of good runners in a population will lead to the widespread distribution of a “runners” genotype and phenotype within that population over time. I know of no evidence to support your assertion, only evidence to the contrary. However, there are clearly indigenous populations that did not use persistence hunting and likely did little long distance running. For example, the various pigmy populations in Papua New Guinea, living in tropical forest environments, may not be good distance runners. The indigenous populations of east Africa, on the other hand…

    I’m also a bit confused as to what should be concluded from your “lack of evidence” and “correlation does not equal causation” comments. You seem to imply that an absence of evidence is evidence of absence (i.e. supportive of the null hypothesis of no difference/no benefit), when clearly it is nothing more than no evidence (i.e no information to support any hypothesis or conclusion). Yet, there is some evidence accumulating to suggest that minimalist or barefoot running, in adapted and conditioned barefoot runners, improves running economy and reduces the incidence of injury. At the same time, I’m not aware of any evidence accumulating to support any similar benefits from conventional trainers. Anyone with a bit of epidemiology and biostatistical knowledge can use the “methodological flaw” or “confounding variables” defense against any study. I doubt we are going to see highly powered RCTs when it comes to running footwear and, as for “causation”, what criteria shall we use to define causality?

    I do agree that most adult individuals are deconditioned from our sedentary, non-pedestrian, culture and would need to slowly recondition into barefoot running. I think part of this deconditioning is the result of unnecessarily over-engineered footwear. Modern running trainers are like an immobilizing brace for the foot arch, especially if one uses orthotics. Put an immobilizing brace on your elbow for a few months and see what happens. Indeed, you’ll need an even stronger brace to prevent your elbow from getting injured from routine use.

    You did not mention the obvious, probably because it is obvious, but the modern environment presents numerous hazards to completely barefeet (glass, nails, toxicants, etc.). Minimalist footwear is the middle way here, so shoe companies should not fear the barefoot trend.

    Finally, I agree fully that much of the benefit of the barefoot running boom comes from an increased public (running public) awareness to running biomechanics and economy. These are the same biomechanics that have been promoted in the elite running community for at least a century, only gaining more widespread attention just recently with Chi Running and Pose Method. There is nothing new under the sun here, just different ways of communicating the same thing.

    I don’t like fads, and I don’t like it when one journalist author or trade book gets all the attention for a perspective developed and advanced by a huge collective of hard working researchers, but I do think barefoot/minimalist running is based on very strong premises and has robust convergent validity. The evolutionary argument is a powerful one, despite not being politically popular and being tarnished by widespread misconceptions of human evolution and evolution in general.

    I’ll stop here. Thanks for reading and, however you run, run on!


    • Nathn,

      Thanks for reading and thanks for taking the time to comment. I do love feedback, even when we disagree. Let me respond to your comments.

      Natural Selection: I do believe in evolution. I also believe that we lived in societies and not as solo hunters. So, there was specialization; the hunters hunted, gatherers gathered, care givers took care, etc. There’s tremendous variation not only within cultures, but even within families. For example, my dad and I are about the same height, but I’m built more like a runner and he like a wrestler; my brother who looks more like my father, was a gymnast.

      Lack of evidence: That’s not what I’m saying; I’m sorry if that was the implication. What I was doing was countering the rush to barefooting and belief that the science is clearly on their side. It’s Lieberman himself who says, “Please note that we present no data on how people should run, whether shoes cause some injuries, or whether barefoot running causes other kinds of injuries. We believe there is a strong need for controlled, prospective studies on these issues.” I suspect that they believe that forefoot is key, so that’s what they look for, and that’s what they are likely to find (confirmation bias). Instead, I think that forefoot may be a proxy for COG.

      I urge you to look at the UVA studies the seem to show that COG is more important than forefoot. While COG and forefoot may be highly correlated, I think the focus on forefoot instead of COG misleads people. Eliminate overstriding and you will eliminate a lot of running problems, and also get most runners to forefoot strike most of the time.

      However, even then, there’s evidence that as runners fatigue in longer races, even the elite, efficient runners are more likely to heel strike later in longer races. I would guess that while heel striking, the efficient runners are still landing under their COG. That speaks to the benefit of shoes with some cushioning.

      As I stated, I think the main benefit from minimalist shoes may be that it allows/forces your foot muscles to work and strengthen. Thus, a lightweight, unstructured trainer or racing flat might be as good as or even better than a Vibram Five Fingers or Merrill Glove. They allow your foot to work naturally, while also giving you the cushioning necessary for when your foot fatigues. Another idea is to remove the insole from your running shoe, something I’ve been doing for years. I will speak more about shoes and ways to strengthen your feet in part 2.

      I encourage you (and others) to respond.

      • Hi Adam,
        Thank you for the thoughful reply and openness to debate, or rather dialogue as it is.

        I accept your argument that it may be all about COG rather than forefoot striking. I do not thinik a conscious focus on forefoot striking necessarily leads to efficient biomechanics. It is obviously much more complex, involving the entire body and mind. A COG focus may indeed be more effective at “retraining” ones running form. I’m grateful that so many approaches to the same ends exist (Chi, Pose, Barefoot, etc.) as the same thing communicated with different concepts ultimately reaches a larger population. But I do think the benefits of these techniques are reaching at the same thing, and, you are right, COG is a common thread.
        I still firmly disagree, however, that natural selection, operating at the genetic or group levels anyway, could result in genetic and, therefore, phenotypic specialization within common lineages sharing the same ecology. Specialization within bands may have existed to some degree, though this “specialization” was usually very general and related to gender and age. Phenotypically speaking, specialization is most apparent by gender in the form of sexual dimorphism. For highly beneficial traits, such as running, sexual selection and natural selection tend to promote sexual monomorphism, effectively eliminating genotypic and phentoypic specializaton. I think humans are born to run as much as a bird is born to fly (they walk too!).
        Thanks again for the interesting dialogue!


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