Friday, August 26, 2005

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.