Friday, July 22, 2011

What a big nose you have Mr. Neanderthal....but why?

Todd Rae and colleagues argue that the Neanderthal face was not adapted for extreme cold in this article in the Journal of Human Evolution.

The paper tackles two major assumptions about the paranasal sinuses: (1) big paranasal sinuses are good for surviving really cold weather and (2) that Neanderthals had really big paranasal sinuses. 

The authors conducted a study of 2D and 3D X-rays on a sample of humans, other primates, and rodents.  They showed that arctic critters actually exhibit smaller paranasal sinuses, not larger ones.  Furthermore, when you correct for the size of the cranium, the sinuses of Neanderthals weren't any bigger than those of humans living in temperate latitudes. 

Thursday, July 21, 2011

The Evolution of Grandparents

 Rachel Caspari discusses the evolution of grandparents in this interesting Scientific American article. 

Using dental techniques for estimating age based on the degree of tooth wear and dental eruption sequences, Caspari and colleagues calculated a simple ratio of old individuals (>30 years) to young individuals (<30 years). They discovered that the number of old individuals increased slowly from australopithicines onward, but the number skyrocketed upward in modern humans of the Upper Paleolithic. Caspari argues that increased numbers of oldsters, possibly as a result of some cultural shift, started a positive feedback loop which led to increasing cultural complexity in modern humans during the Upper Paleolithic.  In other words, learning the complex behaviors characteristic of modern humans becomes possible when you have your wise old granny and grandpa to teach you. 

Thanks to Mimi Myrtille for bringing this article to my attention in a Facebook Post. 

Wednesday, July 20, 2011

Where did modern humans come from?

Most everyone agrees the general answer to that question is "Africa" but recently there has been some debate as to where in Africa the earliest modern humans (H. sapiens) came from. In a previous post I discussed an argument that the source population might have been of North African origin.  The paper arguing for a North African origin was actually a response to this paper by Henn and colleages, who conducted a genetic analysis of living hunter gatherers.  Their results indicate that Southern African hunter gatherer populations have greater genetic diversity than hunter-gatherers in other parts of Africa, thus these populations are inferred to be older. I am slightly uncomfortable with this conclusion, because I don't understand how the authors can rule out the existence of more ancient modern human populations in other parts of Africa which have not survived to the present day.  But, on second thought, wouldn't that same argument apply to any argument based on modern human genetic diversity?

Both the North African and Southern African arguments are in conflict with the most commonly accepted notion that modern humans evolved in East Africa.  An East African origin is supported by the fact that Ethiopia is home to the oldest fossil evidence of modern humans from Omo Kibish (McDougall et al., 2005, news story), as well as the slightly younger fossils from Herto in the Middle Awash.

Tuesday, July 19, 2011

Did Neanderthals Bury Their Dead?

Image © Emmanuel Roudier, 2008
Sandgathe et al. take up this question in an article in early view in the Journal of Human Evolution entitled "The Roc de Marsal Neandertal child: A reassessment of its status as a deliberate burial".  The child from Roc de Marsal has been considered by many to be a deliberate burial. Sangathe and colleagues question the child's status as a burial on several grounds: the position of the body (on its stomach with partially flexed legs), the lack of distinctive burial objects (grave goods), among others.  They even argue that the hole the child was buried in was a natural depression, not a (cave)man-made grave pit.  I find their arguments fairly convincing....which makes me think critically about how quickly we are willing to attribute modern-human like behaviors to ancient human ancestors.

Monday, July 18, 2011

"Boxing" Hypothesis for the Origins of Bipedalism

Add this to the list of published ideas about the selective advantages of bipedalism.

In a PLOS One article Carrier reports that human subjects deliver more powerful punches from a bipedal (orthograde) posture than from a quadrupedal (pronograde) posture.  This might suggest that forelimb fighting among males competing for females is a selective pressure for bipedalism.

Maybe we can call it the Rocky Hypothesis?

Sunday, July 17, 2011

Geographic variation in Neanderthal diets

Zaatari et al. report (in an early view article in the Journal of Human Evolution) on the diets of a large sample of Neanderthals from across their geographic range, inferred using molar microwear texture analysis.  Results support previous studies indicating Neanderthals ate lots of meat...but the analysis revealed significant variability in the amount of plant foods incorporated in the diet.  I find this interesting for several reasons, including the current "Paleo Diet" craze I have been hearing about lately.  Even Neanderthals, a temporally and geographically restricted group, had significant variability in their diet....imagine the amount of variability in the much more ecologically diverse groups of modern human foragers the paleo-diet folks are trying to mimic. Which paleodiets should I try to follow?  The highly carnivorous ones? or the mostly vegetarian ones?