A 26,000 year-old early modern human, Dolni Vestonice 16 from the Czech Republic, showing the reduced strength of the bones of the lesser toes. It is one of three partial foot skeletons from Dolni Vestonice that shows the reduced lesser toe strength, all dating to about 26,000 years ago. (Photo Credit: Erik Trinkaus / Czech Academy of Sciences)
He analyzed the the feet of middle and upper Paleolithic humans and compared the strength of the toes (based on robusticity, size of muscle markings, etc.) with leg strength (I'm assuming this means the tibia and fibula - again based on robusticity, size of muscle markings, etc.). Trinkaus notes that around 30,000 years ago toe strength underwent a reduction while calf strength remained the same. He chalks up this decrease in toe strength to the full time use of supportive footwear:
During barefoot walking, the smaller toes flex for traction, keeping the toe bones strong. Supportive footwear lessens the roll of the little toes, thus weakening them.
Trinkaus is certainly one of the more original thinkers in Paleoanthropology, but I am a little bit skeptical. Granted, I haven't read the article in the October Journal of Archaeological Science (abstract available here - so if someone out there with access wants to send me a copy of the article...?). My first thought on reading the Science Daily article was what about allometry and/or sexual dimorphism?
Added Later: Go here for more.