This is getting longhaired but interesting. From Wikipedia
At the individual organism level - phenotypic plasticity
The ability of an organism with a given genotype to change its phenotype in response to changes in the environment is called phenotypic plasticity.[1] Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship of a range of environments to a range of phenotypes.
A highly illustrative example of phenotypic plasticity is found in the social insects, colonies of which depend on the division of their members into distinct castes, such as workers and guards.[4] These two castes differ dramatically in appearance and behaviour. However, while these differences are genetic in basis, they are not inherited; they arise during development and depend on the manner of treatment of the eggs by the queen and the workers, who manipulate such factors as embryonic diet and incubation temperature. The genome of each individual contains all the instructions needed to develop into any one of several 'morphs', but only the genes that form part of one developmental program are activated.[5]
At the cellular level - epigenetics
Epigenetics refers to changes in gene expression. These changes may remain through cell divisions for the remainder of the cell's life. Sometimes the changes last for multiple generations. However, there is no change in the underlying DNA sequence of the organism,[1] instead, environmental factors cause the organism's genes to behave (or "express themselves") differently.[2] The best example of epigenetic changes in eukaryotic biology is the process of cellular differentiation. During morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo which in turn become fully differentiated cells. In other words, a single fertilized egg cell - the zygote - changes into the many cell types including neurons, muscle cells, epithelium, blood vessels et cetera as it continues to divide. It does so by a process of activating some genes while silencing others.[3]
The role of phenotypic plasticity in driving genetic
evolution
Trevor D. Price1*, Anna Qvarnstro¨m2 and Darren E. Irwin3
Models of population divergence and speciation are often based on the assumption that differences
between populations are due to genetic factors, and that phenotypic change is due to natural selection.
It is equally plausible that some of the differences among populations are due to phenotypic plasticity.
Phenotypic plasticity is widespread in nature and may speed up, slow down, or have little effect on evolutionary
change. Moderate levels of plasticity may often facilitate genetic evolution but careful analyses of individual
cases are needed to ascertain whether plasticity has been essential or merely incidental to population differentiation.
Comparisons of populations of the same species on continents
and islands have demonstrated differences in foraging
behaviours (MacArthur & Wilson 1967; Yeaton
1974; Blondel et al. 1988; Prodon et al. 2002). Similar
comparisons have also demonstrated differences in morphology
(Clegg & Owens 2002). In individual cases the
behavioural and morphological differences have been
directly connected (e.g. Yeaton 1974; Grant 1979; Feinsinger
& Swarm 1982).