 The end of the twentieth century brought discoveries that challenged prevailing genetic determinism, and also began to replace the extreme forms of either preformationism or epigenesis with the sorts of interactionist models that were only offered as outlying alternatives in earlier decades. A modified form of epigenesis, in which the organism is seen as beginning from an inherited egg and sperm that do include genes, seems to be on the rise again. Research on cell development, stem cells, and tissue engineering shows that the identity of any particular cell is not predetermined, but also depends on interactions with its neighbors and context. Ian Wilmut’s team’s success in cloning Dolly, reported in 1997, and John Gearhart and James Thomson’s successes with developing human stem cell lines, both reported in 1998, challenged prevailing assumptions (Wilmut et al 1997, Wilmut, Campbell, &amp; Tudge 2000; Thomson et al. 1998; Shamblott et al. 1998; Gearhart 1998). Both suggested that development is a good deal more flexible, plastic, and interactive than preformationist interpretations allow. These experimental results, alongside conceptual issues, spur alternative theories of development. Gilbert (2004) notes increased emphasis on interaction, change, emergence, and reciprocal “determination” relations between whole and component parts. His own work emphasizes the need for multiple perspectives in understanding development; notably diversification in the location of causal control beyond genes alone (see the entry on  evolution and development).  This section focuses on philosophical efforts along these lines.