a mechanism called genetic assimilation which would allow an animal's response to an environmental stress to become a fixed part of its developmental repertoire, and then went on to show that the mechanism would work. In 1972, Waddington founded the Centre for Human Ecology in the University of Edinburgh. Epigenetic landscape Waddington's epigenetic landscape is a metaphor for how gene regulation modulates development. Among other metaphors, Waddington asks us to imagine a number of marbles rolling down a hill. The marbles will sample the grooves on the slope, and come to rest at the lowest points. These points represent the eventual cell fates, that is, tissue types. Waddington coined the term chreode to represent this cellular developmental process. The idea was based on experiment: Waddington found that one effect of mutation (which could modulate the epigenetic landscape) was to affect how cells differentiated. He also showed how mutation could affect the landscape, and used this metaphor in his discussions on evolution—he emphasised (like Ernst Haeckel before him) that evolution mainly occurred through mutations that affected developmental anatomy. Genetic assimilation Waddington proposed an evolutionary process, "genetic assimilation", as a Darwinian mechanism that allows certain acquired characteristic to become heritable. According to Navis, (2007) "Waddington focused his genetic assimilation work on the crossveinless trait of Drosophila. This trait occurs with high frequency in heat-treated flies. After a few generations, the trait can be found in the population, without the application of heat, based on hidden genetic variation that Waddington asserted had been "assimilated". Neo-Darwinism versus Lamarckism Waddington's theory of genetic assimilation was controversial. The evolutionary biologists Theodosius Dobzhansky and Ernst Mayr both thought that Waddington was using genetic assimilation to support Lamarckian inheritance. They denied that genetic assimilation had taken place, and asserted that Waddington had simply observed the natural selection of genetic variants that already existed in the study population. Other biologists such as Wallace Arthur disagree, writing that "genetic assimilation, looks, but is not Lamarckian. It is a special case of the evolution of phenotypic plasticity". Adam S. Wilkins wrote that "[Waddington] in his lifetime... was widely perceived primarily as a critic of Neo-Darwinian evolutionary theory. His criticisms ... were focused on what he saw as unrealistic, 'atomistic' models of both gene selection and trait evolution." In particular, according to Wilkins, Waddington felt that the Neo-Darwinians badly neglected the phenomenon of extensive gene interactions and that the "randomness" of mutational