Afarensis is a 3.5-2.8 million year old hominin from the Kada Hadar member of the Hadar formation in the Middle Awash, Ethiopia. He is approximately 41 inches tall, weighs approximately 60 pounds and has a cranial capacity of a whopping 410 cc (approximately). Afarensis is currently considered to be transitional between apes and humans and displays some traits of both. Since he spends a lot of time on the couch watching monster movies, some observers question whether he is an obligate biped (although no one has observed him climbing a tree). He also has a blog called 
The American Museum novitates has an interesting paper - made all the more interesting by the fact that it is freely available for download. The main focus of the paper is to determine which craniodental measures give reliable estimates of body mass. To that end, the authors examined over 80 variables were measured on 157 specimens representing 17 species. Specimens were chosen so that all platyrrhine genera were represented and the full range of body sizes in platyrhines was represented as well. Regression formulas were then created and applied to Chilecebus carrascoensis - a Miocene Primate from Chile.
This is where the study gets interesting (well, actually, the study got interesting during the discussion of allometry, but that is outside the scope of this post). Primates have large brains compared to body mass. One question has always been whether this is an ancestral condition characteristic of the Anthropoidea, or whether it developed independently in catarrhines and platyrrhines. This paper comes down on the side of independent development. The authors go on to say:
If confirmed, this evolutionary pattern in Primates would mirror independent increases in encephalization observed across mammalian lineages (Jerison, 1970; Radinsky, 1971; Martin, 1984), and within subclades of Carnivora (Finarelli and Flynn, 2007; Finarelli, 2008) and the Cetacea (Marino et al., 2004). The convergent acquisition of higher degrees of encephalization in platyrrhines and catarrhines may yield insights into the evolutionary history of these features in other clades.
Life Science
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I understand that R. Wrangham theorizes that large brain size relative to gut size is not strictly a primate feature, but occurs widely throughout the animal kingdom due to diet. Animals that eat a relatively high calorie, high protein and fat diet can get by with a smaller, shorter intestinal tract and will generally evolve larger brains. Conversely, animals that eat protein-poor, high-fiber diets will require larger intestinal tracts and will generally make due will fairly small brains. I mentioned this in my book (available on Amazon's "Kindle") entitled "The Human Journey."
Posted by: Diana Gainer | July 14, 2008 8:21 AM