There are numerous studies exploring mechanisms of adaptation to selective pressure in various organisms, in which many hypothesize it being a predominant force in evolution. Although adaptation is a basic and crucial mechanism affecting biology as a whole, we still remain in the dark about it. One aspect regarding selective pressure and how it affects us over generations is stress and trauma, which afflict most of us at some point of our lives (89 % of Americans). Numerous studies suggest that extreme environmental factors, such as trauma, change how DNA is being used in organisms to produce functioning proteins, which is supposed to play an important role, among other things, in neural plasticity. This form of direct adaptation to selective pressure is not realized through random classic mutations, and therefore presents a fast tool set for an organism to integrate environmental information, which is supposed to be passed down to next generations. While epigenetic mechanisms, such as DNA methylation, are involved in adaptation in one organism, this is not a likely system to pass down information of adaptation to next generations for two reasons: 1)There are no known mechanisms how trauma that cause changes in neurons would affect fully formed germline cells before fertilization through methylation.2)Even if germline cells would be modulated by trauma through methylation, these marks would most likely not survive to a significant enough extend, because of the various stages of methylation resetting mechanisms after fertilization and throughout development.An alternative system by which trauma adaptation could be transmitted to next generations, would be that of transposable elements (TEs). Traditionally they have been considered as junk DNA, which means that although representing a high proportion of genomes (ca. 45 %) no cellular functions could be detected. However, recently it has become evident that TE-derived DNA sequences not only play a fundamental role during evolution in all organisms, but that TEs are also implicated in the origin and evolution of various disorders. Therefore, one could hypothesize, that TEs play a crucial role in adaptation in general, and especially to trauma.
DNA methylation from germline cells in veterans with PTSD