Evolution leads to phenotypic changes through changes in DNA such as mutations. Mutations are transmitted to offspring. Cumulative mutational changes across many generations may cause evolution and speciation.
As far as I know, epigenetic changes causes an individual to change in how it appears (phenotypic changes). In turn, epigenetic changes may be transmitted to offspring, just as DNA mutations can be.
Is epigenetics a factor in evolution?
To start I will repost some of an answer I have previously posted, which will explain what evolution is:
Evolution is simply a process of change. It is a change in trait values of populations over time. It results from four mechanisms: mutation, migration, drift, and selection.
"Evolution means change, change in the form and behaviour of organisms between generations. ... When members of a population breed and produce the next generation we can imagine a lineage of populations, made up of a series of populations through time. Each population is ancestral to the descendant population in the next generation: a lineage is an ancestor-descendent series of populations. Evolution is then change between generations within a population lineage." - Ridley, Evolution
Your Answer:
Evolution depends on the inheritance of information from the ancestral population to the descendant population. Much of the time we talk about information in the form of genetic variation, the information contained within the DNA. However, more and more we are realising that other forms of information transmission can occur, including epigenetic effects, and that these can contribute to evolution.
"Epigenetic modifications are a bit like ornaments on a Christmas tree; the tree (the DNA sequence) is still the same, but the decorations (epigenetic modifications) change how it's perceived." ...
"Over the past few years, several studies have compared the epigenetic modifications of our genome with that of other great apes, leading to an emerging picture of the importance of epigenetics in our recent evolutionary history." ...
"The role of epigenetics in evolution (particularly primate evolution) is an active and exciting area of research..." - Nature Scitable
The edited question is also broad in scope, but one can narrow it down by talking about specific conditions. For example, the role of epigenetics markers helping in survival under stress conditions, especially in A. thaliana, has begun to be much appreciated.
Epigenetics could also potentially be an important mechanism facilitating developmental plasticity-formation of two or more phenotypes from the same genotype, a process which helps organisms to adapt to changing environments (Developmental Plasticity and Evolution-Mary Jane West Eberhard, Oxford Univ. Press 2003).
Under both scenarios described above, epigenetic changes could favour a differential success in survival (e.g. under stress) and/or reproduction (e.g. flowering) of individuals in a population as compared to animals without these markers, thus leading to evolution in the next generation.
