 The second major discovery that promoted evo-devo was the discovery of modular enhancers. The above-mentioned transcription factors would bind to specific regions of DNA, called enhancers. Most genes have multiple enhancers. Thus, a gene might have a ‘limb’ enhancer that activates the expression of the gene in the limb, and an ‘eye’ enhancer that enables the expression of the gene in the eye. Moreover, each enhancer usually binds several transcription factors and could be activated in Boolean &lt;and&gt; or &lt;or&gt; fashion. Evolution could occur by creating or deleting enhancers, thereby enabling genes to be expressed differently in different species. King and Wilson (1975) and Jacob (1977) had speculated that evolution occurred by changes in gene regulation. This provided a model for such regulation, and some of the best examples are seen in the divergence of humans from other apes (Geschwind &amp; Konopka 2012; Pollard et al. 2006). As Haraway (2008) noted, “relationships are the smallest possible pattern for analysis”, and the relation between enhancer and transcription factor may indicate the ‘natural kinds’ of the biological world (Gilbert &amp; Bard 2014). Moreover, the entities defined by enhancer/transcription factor interactions during development are often unexpected and do not mirror intuitive boundaries between entities in adults. Activation of genes to form the distal rib, for instance, is controlled by a different enhancer than that which activates genes in the proximal rib (Guenther et al. 2008).