Epigenetics is a fairly recent emerging science. It is the study of phenotypic changes that are caused by the modification of gene expression rather than the modification of the DNA itself. The epigenome is made up of the chemical compounds that have been added to DNA as a way of regulating gene expression within the entire genome. The compounds themselves are not a part of the DNA sequence. They attach to the DNA, and things like diet and pollutants can affect the epigenome.
Epigenetic changes can influence whether or not genes are turned on. This results in influential changes in protein production. There might not be any problem with this; however, errors in the epigenetic process can cause modifications to incorrect genes, and that could lead to genetic disorders of various kinds.
Until recently, scientists used to think that an embryo's epigenome was a blank slate. The thinking was that a person's epigenetic tags were erased or reprogrammed, thus preventing the epigenetic tags from being passed down from generation to generation. This thinking is no longer valid. Scientists have discovered that some of the parent's epigenetic tags stay in place and are passed down to the next generation. This process is called epigenetic inheritance.
That might sound bad, and there are definitely negative implications; however, a positive implication is that the epigenome can rapidly change phenotypic expression in response to environmental signals. This ability to rapidly change/adapt to an environment alters the fitness of an individual or species which contributes to evolutionary changes.