Evolution of Human Limb Proportions: Part Two

As I mentioned in Part One The OH62 femur plays an important role in any discussion of the evolution of human limb proportions.

Looking at the above picture, several things should be noticed. First, the head and a small portion of the neck are missing. Second, the shaft extends to a little past the nutrient foramen (although you can’t really see this in the picture – for those unfamiliar with osteology the nutrient foramen is an opening for the passage of blood vessels and bone). Third, there is a significant amount of bone exfoliation. In order to determine femur length an estimation needs to be made.

Evolution of Human Limb Proportions: Part One

Humans have interesting limbs. Unlike in the apes, the humerus is shorter than the femur but longer than the radius. In chimps and gorillas the humerus is longer than the femur and radius. In orangutans and gibbons the humerus is longer than the femur but shorter than the radius. There are several measures anthropologists use to make these determinations. One, the humerofemoral index ([humerus x 100]/femur) measures the ratio of humerus to femur. In humans the mean of this index is (approximately) 71, in chimps 101, gorillas 116, orangutans 130 and in the gibbon 116. To compare the humerus and radius the brachial index ([radius x 100]/humerus) is used. Mean values are: humans 74, chimps 92, gorilla 80, orangutan 100 and gibbon 110. Since humans and chimps share a, relatively, recent common ancestor presumably some evolution has occured in limb proportions. We can look at the postcranial skeletons of a few hominids to determine a rough time line. Australopithecus afarensis, for example, has a humerofemoral index of about 84 (largely attributed to a smaller femur) and a brachial index of about 91 (larger radius relative to humerus). In Homo erectus, on the other hand the humerofemoral index is approximately 73 and the brachial index is 79 or roughly the same as in modern humans. So, during the course of human evolution there have been changes in forearm proportions and in femur length. For quite a while this was interpreted as an example of gradualism in hominin evolution. Then, the fly in the ointment was found.

Homo floresiensis

The April issue of National Geographic has an interesting article on Homo floresiensis. The article is written by Mike Morwood, Thomas Sutikna and Richard Roberts. The basics of the find are covered (who, what, when, where, etc)and brief mention is made of the microsephaly issue, but the find is presented as legitimate. They cover other issues such as island dimorphism and provide some interesting info concerning the archaeology of the site. This may be intersting.
A second article, by Josh Fischman, covers finds of Homo erctus at Dmanisi, Georga. The main emphasis of the article is on one of specimens that was toothless. More importantly, the mandible shows signs of bone resorption – indicating the individual survived after loosing his teeth. In this respect this find is similar to finds of later neanderthals. The author also discuss the spread of H. erectus out of Africa, and of course, links it to the H. floresiensis finds. One of the more interesting pieces of information in the article is that the Dmanisi fossils were smaller than the african or asian erectus specimens (excepting H. floresiensis). Height is around four and a half feet and cranial capacity averaged 650 cc’s. Some traits displayed by the four skulls are similar to H. habilis and one of the discovers, David Lordkianidze, is quoted as saying “… this is something between habilus and erectus, and maybe it’s the founder of erectus”.

Interesting, I really need to get to a library and catch up on whats been happening in the world of Paleoanthropology.