For Darwin, the object of evolutionary discourse, the biological individual, was unambiguously the organism. But since Darwin the locus of biological individuality has become more ambiguous. Not necessarily indivisible, the individual remains bounded and delineated, assumed apriori to be differentiable because it stands apart from, independent of, others. By contrast, the component parts that comprise the individual unit are bound in necessary union. Although the individual pictured as organism continues to underlie most discussions, David Hull (1984) offers us a more general definition: "Individuals are spatiotemporally localized, internally cohesive entities that develop continuously through time." They may be species, groups, organisms, or genes.