Statistical Analyses Cannot be Divorced From Archaeological Theory: A Reply to Potter

Potter criticizes our experimental study of the roles played by indirect bias and guided variation in shaping prehistoric Great Basin projectile point variation. His criticisms are technically correct from the standpoint of statistical convention, but he fails to understand the theoretical rationale of our study. Without such an understanding, hi s assertion that our conclusions are questionable is incorrect. Here we point out again (1) how our experimental work bridges the gap between cultural-transmission theory and the empirical record and (2) why our conclusions are indeed valid

The Cultural Transmission of Great Basin Projectile-Point Technology I: An Experimental Simulation

A Darwinian evolutionary approach to archaeology naturally leads to a focus on cultural transmission. Theoretical models of cultural evolution indicate that individual-level details of cultural transmission can have specific and significant population-level effects, implying that differences in transmission may be detectable in the archaeological record. Here we present an experimental simulation of the cultural transmission of prehistoric projectile-point technology, simulating the two transmission modes-indirect bias and guided variation-that Bettinger and Eerkens (1999) suggested were responsible for differences in Nevada and California point-attribute correlations. Groups of participants designed virtual projectile points and tested them in virtual hunting environments, with different phases of learning simulating, alternately, indirectly biased cultural transmission and independent individual learning. As predicted, periods of cultural transmission were associated with significantly stronger attribute correlations than were periods of individual learning. We also found that participants who could engage in indirectly biased horizontal cultural transmission outperformed individual-learning controls, especially when individual learning was costly and the selective environment was multimodal. The study demon-strates that experimental simulations of cultural transmission, used alongside archaeological data, mathematical models and computer simulations, constitute a useful tool for studying cultural change

IV.3. Bioreactors in tissue engineering.

IV.3. Bioreactors in tissue engineering

Cultural Evolutionary Tipping Points in the Storage and Transmission of Information

Human culture has evolved through a series of major tipping points in information storage and communication. The first was the appearance of language, which enabled communication between brains and allowed humans to specialize in what they do and to participate in complex mating games. The second was information storage outside the brain, most obviously expressed in the Upper Paleolithic Revolution - the sudden proliferation of cave art, personal adornment, and ritual in Europe some 35,000-45,000 years ago. More recently, this storage has taken the form of writing, mass media, and now the Internet, which is arguably overwhelming humans\u27 ability to discern relevant information. The third tipping point was the appearance of technology capable of accumulating and manipulating vast amounts of information outside humans, thus removing them as bottlenecks to a seemingly self-perpetuating process of knowledge explosion. Important components of any discussion of cultural evolutionary tipping points are tempo and mode, given that the rate of change, as well as the kind of change, in information storage and transmission has not been constant over the previous million years

Influence of a novel calcium-phosphate coating on the mechanical properties of highly porous collagen scaffolds for bone repair.

Lyophilised collagen scaffolds have shown enormous potential in tissue engineering in a number of areas due to their excellent biological performance. However, they are limited for use in bone tissue engineering due to poor mechanical properties. This paper discusses the development of a calcium-phosphate coating for collagen scaffolds in order to improve their mechanical properties for bone tissue engineering. Pure collagen scaffolds produced in a lyophilization process were coated by immersing them in sodium ammonium hydrogen phosphate (NaNH(4)HPO(4)) followed by calcium chloride (CaCl(2)). The optimal immersing sequence, duration, as well as the optimal solution concentration which facilitated improved mechanical properties of the scaffolds was investigated. The influence of the coating on composition, structural and material properties was analysed. This investigation successfully developed a novel collagen/calcium-phosphate composite scaffold. An increase in the mechanical properties of the scaffolds from 0.3 kPa to up to 90 kPa was found relative to a pure collagen scaffold, while the porosity was maintained as high as 92%, indicating the potential of the scaffold for bone tissue engineering or as a bone graft substitute

Osteoblast response to rest periods during bioreactor culture of collagen-glycosaminoglycan scaffolds.

Flow perfusion bioreactors have been shown to enhance fluid transport and improve cell viability throughout tissue-engineered bone constructs. Furthermore, osteoblasts have been shown to be stimulated by flow during bioreactor culture, although the optimum flow regime to promote an osteogenic response has yet to be found. One problem is that bone cells lose their ability to respond to stimulation; however, mechanosensitivity can be restored by introducing resting periods between bouts of loading. The aim of this study was to analyze the effect of rest-insertion on the response of osteoblasts seeded on collagen-glycosaminoglycan scaffolds in a flow perfusion bioreactor over culture periods up to 14 days. Short-term rests of 5, 10, or 15 s and long-term rests of 7 h were incorporated into stimulation patterns. Cell distribution was enhanced in all flow groups, whereas static culture controls exhibited encapsulation. Cyclooxygenase-2 expression and prostaglandin E(2) levels increased significantly because of bioreactor culture over static controls. Osteopontin expression was significantly higher for the rest-inserted groups than the static control group or steady-flow group. These results indicate that the insertion of resting periods during flow enhances cellular distribution and osteogenic responses on collagen-glycosaminoglycan constructs cultured in a flow perfusion bioreactor

Hair Bundle Morphology on Surviving Hair Cells of the Chick Basilar Papilla Exposed to Intense Sound

Exposure to intense sound produces a well-defined patch lesion on the chick basilar papilla in which 30-35% of the short hair cells are lost. The present study compares various aspects of sensory hair bundle morphology on surviving hair cells in the patch lesion with hair bundles from matched locations on nonexposed control papilla immediately after removal from the exposure and 12-days post exposure. The height and thickness of the hairs, the total number of hairs in the bundle, the width of the bundle, and the area and perimeter of the apical surface of the hair cell were quantified from scanning electron microscope photomicrographs. An attempt was also made to determine if there was a consistent microstructure to the pattern of hair cell loss within the lesion area. Similar observations in 12-day recovered ears are also presented. The results indicated that stereocilia height increased and width decreased on surviving hair cells in the exposed ear. The width of the hair bundle, the hair cell surface area, and perimeter also decreased. However, the number of hairs per cell remained unchanged, and there was no evidence of any consistent organization to the hair cell loss within the patch across a number of specimens. These observations indicated that the hair bundles on short hair cells underwent changes as a consequence of intense sound exposure.The results after 12 days of recovery were complicated by developmental changes on the papilla and incomplete maturation of the newly regenerated hair cells. It remains to be seen whether these changes were the result of cell sampling in the sound-damaged ear or were due to true structural alterations within the sensory hairs themselves

Stimulation of osteoblasts using rest periods during bioreactor culture on collagen-glycosaminoglycan scaffolds.

Osteoblasts respond to mechanical signals which play a key role in the formation of bone however, after extended periods of stimulation they become desensitised. Mechanosensitivity has been shown to be restored by the introduction of resting periods between loadings. The aim of this study was to analyse the effect of rest periods on the response of osteoblast-like cells seeded on collagen-glycosaminoglycan (CG) scaffolds in a flow perfusion bioreactor up to 14 days. Short (10 s) and long (7 h) term rests were incorporated into stimulation patterns. Constructs cultured in the bioreactor had a more homogenous cell distribution albeit with lower cell numbers than the static group. Osteopontin expression was significantly higher on the rest-inserted group than on the steady flow and static control. These results indicate that the insertion of short term rests during flow improves cellular distribution and osteogenic responses on CG constructs cultured in a flow perfusion bioreactor