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Journal Article

A Model Relating Developmental Interaction and Differential Evolutionary Reduction of Tooth Size

J. A. Sofaer
Evolution
Vol. 27, No. 3 (Sep., 1973), pp. 427-434
DOI: 10.2307/2407305
Stable URL: http://www.jstor.org/stable/2407305
Page Count: 8
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A Model Relating Developmental Interaction and Differential Evolutionary Reduction of Tooth Size
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Abstract

Reduction in size of the jaws during hominid evolution has been accompanied by a general reduction of tooth size, but within each morphological class the later a tooth develops the more it has been reduced. This pattern of differential reduction can be explained by assuming that a proportion of the reduction that has taken place in the dentition has been secondary to skeletal reduction, through selection for harmony between size of teeth and size of jaws. Primary reduction of jaw size implies that the teeth were always genetically too large for the jaw in which they developed, and under such conditions of restriction were likely to have shown compensatory interaction due to competition for requirements necessary for growth. In order to explain differential reduction of tooth size in terms of selection for harmony between size of teeth and size of jaws it is necessary to show that genotypes with the potential to produce relatively large early and small late developing teeth were likely to have been favoured over genotypes with the potential to produce relatively small early and large late developing teeth. That is, it must be shown that the genotypically large early and small late combination results in a smaller combined phenotype, which is presumably better suited to a reduced jaw. A model that embodies these features has been proposed. The model predicts that among populations of contemporary individuals greater compensatory interaction is associated with greater asymmetry of the late relative to the early developing teeth within a morphological class. A test of this prediction in twelve genetically different samples of mice showed a slight though non-significant tendency in accordance with this prediction for the relationship between first and second molars in both the upper and lower jaws.

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