When Did Humans Start Wearing Shoes: Part Two

Abnormal Interests has linked (Thanks!)to my post on when humans started wearing shoes. He also links to a BBC News story that provides more info than the Science Daily article. As I suggested in the comments to my original article two things needed to be done to make a convincing case. First, a comparison needed to be made between shoe wearing and non-shoe wearing modern humans. From the BBC article:

To test the theory that the more delicate toes resulted from shoe use, the Washington University researcher compared the foot bones of early Native Americans, who regularly went barefoot, and contemporary Alaskan Inuits, who sported heavy sealskin boots.

Again, he identified chunkier toes in the population that routinely went without shoes. The research suggests shoe-wearers developed weaker toes simply because of the reduced stresses on them during their lifetime; it was not an evolutionary change.

Second, I was concerned about how this could be passed on to future populations. As the above quote also shows, Trinkaus is not advocating this as an evolutionary change. Adaptation can occur in many different ways. The more permanent types represent changes in the genetics of the population. Another type (from Stini in his book “Ecology and Human Adaptation”) occurs in response to stress and may persist for a long period of time and occur in individuals rather than populations. Examples would be moving to a higher altitude or muscular hypertrophy (as a response to high activity levels). It is this second sense that Trinkaus is talking about. Bone has two responses to stress. More bone can be laid down or bone can be absorbed. In the case of muscular hypertrophy, mentioned above, the muscle origins and insertions would become larger in order to accomodate the increased muscle size. Another effect would be that increased muscle size means that increased force can be exerted and bone will be laid down to handle that increased force. In the case of human feet, since humans started wearing shoes, according to Trinkaus, there was a decreased stress on the toes so bone was absorbed leading to more gracile toes. As I mentioned in my first post, there was a trend towards more gracile skeletons from Neanderthals to archaic humans to anatomically modern humans (irregardless of whether you go for Out-of-Africa or Multiregional Continuity – or for that matter one’s views of the taxonomy of the above species) so untangling the two is difficult. Having said that, this study certainly turned out to be more interesting than I originally thought.

Added later: Corrected a few typos and changed one sentence for clarity.

4 Responses

  1. It is interesting. I was trying to understand how if one started out with the less thick toes/feet, but because of barefoot and harsher terrain, feet would become thicker and coarser. I can see how the toes and feet would have to adapt. I guess I can also see how the children could be born with feet more adaptable to their surroundings and their children and so on. I hope I don’t sound like I’m rambling.

  2. Nope, you are not rambling. Trinkaus is arguing that this is more like becoming aclimated to, say, a high altitude environment. When that happens lungs get bigger to make up for the decreased oxygen content. It’s not a genetic change, just an individual response.

  3. I thought of this foot-shoe post when I read Pharyngula this morning. He laid out the basics for adaptation so succinctly I thought I’d copy it here:
    “…the prerequisites for demonstrating that a feature is an adaptation. It has to be shown to be the product of genetic variation, it must be shown to influence reproductive success, it needs to have a mechanism shown to work in nature, and it should be shown by experimental manipulation of the trait or environment to have an effect on reproduction…”
    So, if the toe changes had been a result of genetic variation, conferred reproductive success, etc– we would call it an adaptation. All we have with shoe-wearing is a change in toe bones that occur over one lifetime. The trend to more gracile bone structure was occurring anyway, but probably should not be conflated with the wearing of shoes.
    Okay, but what was Trinkaus’ point anyway?

  4. That pretty much hit the nail on the head. This would not be an adaptation. Given that skeletons were becoming more gracile, I think Trinkaus was trying to date a cultural event (shoe wearing) by how it would affect some skeletons. Note he’s not claiming that this happened in all humans -just those that wear shoes. I think he was just seeing if these kinds of cultural innovations had an impact. The more I think about it the more it reminds me of Brace’s arguments concerning the reduction of anterior dentition in humans (i.e. it was caused by changes in food processing). I’ll have to check out PZ’s post and maybe link to it.

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