A continuum of individuality in modular organisms
1 : University of California - Irvine
Although we often think of individuality as exclusive, such that something is either an individual or it is not, from a biological perspective, we must employ a concept of individuality which admits of degree. By any of the criteria commonly used to define biological individuality, many organisms display an intermediate degree of individuality. Most of these organisms share the characteristic of modular structure. That is, the whole is formed by the iteration of semiautonomous units called modules. The greater the degree of differentiation, integration, and interdependence of these modules, the greater the degree of individuality of the whole. In modular organisms, mutations can introduce intraorganismal genetic heterogeneity, in which case both the parts and the whole can act as units of selection. Selection at the lower level can threaten the integrity of the individual. However, in some cases, selection acts concordantly between levels to the benefit of both. Furthermore, in some cases there may be direct benefits to the higher level of genetic heterogeneity at the lower level. The recognition of intermediate degrees of individuality has led to important biological insights. Therefore, any general, synthetic concept of individuality should take into account these complexities.
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