Two articles in PNAS caught my attention, Rapid dental development in a Middle Paleolithic Belgian Neanderthal & Life history trade-offs explain the evolution of human pygmies. Here are the abstracts:
Recent evidence for developmental differences between modernhumans and Neanderthals remains ambiguous. By measuring toothformation in the entire dentition of a juvenile Neanderthalfrom Scladina, Belgium, we show that most teeth formed overa shorter time than in modern humans and that dental initiationand eruption were relatively advanced. By registering manifestationsof stress across the dentition, we are able to present a precisechronology of Neanderthal dental development that differs frommodern humans. At 8 years of age at death, this juvenile displaysa degree of development comparable with modern human childrenwho are several years older. We suggest that age at death injuvenile Neanderthals should not be assessed by comparison withmodern human standards, particularly those derived from populationsof European origin. Moreover, evidence from the Scladina juvenileand other similarly aged hominins suggests that a prolongedchildhood and slow life history are unique to Homo sapiens.
Explanations for the evolution of human pygmies continue tobe a matter of controversy, recently fuelled by the disagreementssurrounding the interpretation of the fossil hominin Homo floresiensis.Traditional hypotheses assume that the small body size of humanpygmies is an adaptation to special challenges, such as thermoregulation,locomotion in dense forests, or endurance against starvation.Here, we present an analysis of stature, growth, and individualfitness for a large population of Aeta and a smaller one ofBatak from the Philippines and compare it with data on otherpygmy groups accumulated by anthropologists for a century. Theresults challenge traditional explanations of human pygmy bodysize. We argue that human pygmy populations and adaptationsevolved independently as the result of a life history tradeoffbetween the fertility benefits of larger body size against thecosts of late growth cessation, under circumstances of significantyoung and adult mortality. Human pygmies do not appear to haveevolved through positive selection for small stature--thiswas a by-product of selection for early onset of reproduction.
I assume that the case for life history variation between Neandertals and modern humans is evidence for difference, but Pygmies might be different and they're obviously the same species, right? Paleonthropology has a tendency to "bin" different hominids into isolated types and populations, that's just what language does, but it seems like we might make some more concession to traits as a continuous variable and focus more on distributions across the genus and within species (or what we define as species).
Human pygmies do not appear to have evolved through positive selection for small stature--this was a by-product of selection for early onset of reproduction.
The logic doesn't hold. Selection for early onset of reproduction is present in every population in the world, but only in a few did it result in pygmies.
there are usually trade offs (antagonistic pleiotropy).
My point is that what's special about Pygmy populations is not "selection for early onset of reproduction" - there must be something other than that going on.
I've now actually written on each of these, put only the post on "pygmies" is up now:
Hey, that was my first tinyurl. I hope it works!