Tuesday, September 15, 2009

The right-handed ape   posted by Razib @ 9/15/2009 06:20:00 PM

Via Anthropology.net, The prehistory of handedness: Archaeological data and comparative ethology:
Homo sapiens sapiens displays a species wide lateralised hand preference, with 85% of individuals in all populations being right-handed for most manual actions. In contrast, no other great ape species shows such strong and consistent population level biases, indicating that extremes of both direction and strength of manual laterality (i.e., species-wide right-handedness) may have emerged after divergence from the last common ancestor. To reconstruct the hand use patterns of early hominins, laterality is assessed in prehistoric artefacts. Group right side biases are well established from the Neanderthals onward, while patchy evidence from older fossils and artefacts indicates a preponderance of right-handed individuals. Individual hand preferences and group level biases can occur in chimpanzees and other apes for skilled tool use and food processing. Comparing these findings with human ethological data on spontaneous hand use reveals that the great ape clade (including humans) probably has a common effect at the individual level, such that a person can vary from ambidextrous to completely lateralised depending on the action. However, there is currently no theoretical model to explain this result. The degree of task complexity and bimanual complementarity have been proposed as factors affecting lateralisation strength. When primatology meets palaeoanthropology, the evidence suggests species-level right-handedness may have emerged through the social transmission of increasingly complex, bimanually differentiated, tool using activities.

The evolutionary background of handedness is of interest because there are correlates with left-handedness when it comes to individual differences. Handedness can also be somewhat confusing. For example, I am right-handed when it comes to writing (of less relevance today when I generally type). But I am strongly left-handed in basketball, switch-hit in baseball (slower bat speed left), and can throw a football with either arm comfortably (greater strength left, but better touch right, and I tend to side-arm with the left).

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