AQCI

Paleoanthropology Seminar 12th Oct 2000

Evidence that humans evolved from a knuckle-walking ancestor

Brian G. Richmond & David S. Strait

Nature, 23rd March 2000. 404 382-385

General Quotation: Richmond & Strait "present evidence that fossils attributed to A. Anamensis and A. Afarensis retain specialised wrist morphology associated with knuckle-walking."

Argument: Using using cineradiographic methods they examined extant apes (gorilla/chimpanzee) that exhibit knuckle-walking and identified four key skeletal features of the distal radius which seemed to be associated with this form of locomotion. They examined the features in quadrupedal primates that do not knuckle-walk and found that these features were absent.

They measured the four features in A. Anamensis and A. Afarensis distal radius fossils and compared them with the extant species using canonical variates analysis and found that the gracile australopith wrist fell well within the expected range for gorilla whereas the robust form fell under the Homo range.

Question: Is the distal radius the only measurable skeletal adaptation for knuckle-walking? What about the phalanges themselves?

Experiential connection: Richmond & Strait did not give precise details about the samples analyzed and I was not clear what they meant by a "bivariate plot of canonical scores." 

Textual connection: Aiello & Dean (An Introduction to Human Evolutionary Anatomy) p 384, describe the metacarpophalangeal joins (in the fingers) of gorillas and chimpanzees as another adaptation to knuckle walking. 

Implications: The study's most parsimonious explanation is that gracile Australopiths A. Afarensis and A. Anamensis exhibited knuckle-walking.  The study also found that robust australopiths A. Africanus and Paranthropus Robustus did not show evidence of knuckle walking. This has a number of implications.