I. The neo-Darwinistic synthesisThe dominant paradigm in biology, over the second half of the 20th century, called Neo-Darwinism or genetic determinism, has rejected the (Lamarckian) idea that characteristics which were acquired during life can be inherited by next generations. A central concept within neo-Darwinism is the so-called Weismann barrier (the germline) which protects gametes (the sperm and the egg) from being affected by changes in body cells and thus from environmental influences. Because of this, it was thought that only genetic information could be passed on to offspring, not acquired characteristics.
II. What is now known about epigenetics?1): experiences affect gene expression
A finding in epigenetics which is not controversial (anymore) is that experiences affect gene expression. In other words, what happens in our life affects how genes are switched on and off to what extent and thereby which characteristics we will develop. Genes alone do nothing. Our complete development and all our characteristics are the product of the interaction between our genes and our environment.
2): Reliable reproduction of epigenetic effects exists
The degree to which epigenetics affects the development of the individual can be easily underestimated because parents and offspring, in general, share not only genetic factors but also non-genetic factors. Offspring usually growths up in similar environments as parents. Because of this many epigenetic effects can be reliably reproduced in offspring.
3): Inheritance of acquired characteristics through the germline exists
Recent epigenetic research has demonstrated that inheritance of characteristics which were acquired during the lifetime of the parent exists. There are now studies which have shown that epigenetic markers can actually cross the germline (Anway et al., 2005; Franklin et al., 2010; Rakyan et al., 2003), Daxinger & Whitelaw, 2012). Recent research has shown that acquired characteristics can even be transmitted if offspring is not exposed to the same environmental factors which have contributed to the development of those characteristics (Dunn & Bale, 2011; Benyshek et al., 2006).
4): Natural selection operates on any reliably reproduced epigenetic effects by whatever means
Many biologists think that epigenetic effects have no evolutionary consequences but recent research demonstrates that this can actually be the case (Cropley et al., 2012, Skinnner, 2011). In other words, natural selection operates on epigenetic effects which are reliably reproduced over generations.