Evo-Devo does not limit itself to the analysis of phenotypic variation and adaptation, but explicitly addresses the generative mechanisms underlying the evolution of organismal form
(Müller, 2007b: p. 502).
Evo-Devo, or Evolutionary Developmental Biology, combines the two independent research disciplines of Evolutionary Biology and Developmental Biology, that re-joined in the late 1970s and early 1980s, after a break of about 100 years after the ‘biogenetic law’ mostly introduced by Haeckel in the 1860s (Arthur, 2002; Churchill, 2007; Gerson, 2007). Evolutionary Biology explores the evolution of forms that have been realised and their variability, and Developmental Biology proposes morphogenetic mechanisms that could have been explored. Müller (2007b) insisted on the emergence of Evo-Devo from the limitations of these two disciplines to explain the form and the structure of the organisms. Since then, the field of Evo-Devo has become one of the most vigorous parts of biology (Gerson, 2007). In recent years, considerable progress has been made in understanding the developmental basis of morphological evolution (Wagner, 2007). However, to become an independent scientific field, Evo-Devo must prove its potential to induce new scientific questions (Müller, 2007a).
Among the new questions that can be assessed by Evo-Devo, is how development contributes to phenotypic novelty (Müller, 2007a). This question raises the problem of homoplasy, i.e. convergence, parallelism and reversals, in evolution. Are the phenotypic novelties generated by developmental mechanisms homologous or homoplastic? Phenotypic novelties are considered homologous if their similarities between taxa are inherited from a common ancestor, whereas homoplastic traits do not share phylogenetic inheritance (Hall, 2003; Wake et al., 2011). Homoplastic traits that share similar developmental, genetic and/or cell-type mechanisms are considered parallel during evolution, corresponding to the concept of deep-homology (Hall, 2003; Shubin et al., 2009). Homoplastic traits that are defined as convergent are usually observed at greater phylogenetic distances than parallel traits, and may not share similar morphogenetic mechanisms.