Scientific evidence continues to amass sug gestions that predetermined epigenesis is as un tenable a developmental process as preform ationism was. Some scientists have been bridging the gap between molecular biology and develop mental ethology by examining the actual effects of experience on genetic activity (e.g., Mello, Vicario Sc Clayton, 1992). Others have been demonstrating ontogenetic nonlinearities by showing the constructive (rather than merely supportive) role played by seemingly subtle or
nonobvious forms of experience in behavioral development (see also Millei; 1997). Such experi mental evidence suggests that predetermined epigenesis is as anachronistic as preformationism and awaits a similar fate. Were this to be the case, then all epigenesis would be of a probabilistic nature, which would render nativistic thinking untenable and may once and for all lay the na ture-nurture issue to rest. The challenge for sci entists will then be to account for the regulari ties (sometimes referred to as “species-typical behavior”) that we so often observe in behav ioral development. Some contemporary theoreti cal schools (e.g., systems theory and ecological psychology) have been providing an intellectual framework in which developmental scientists working at different levels of organization can meet this challenge.