This 2016 Swiss human review’s subject was:

“Transposable elements (TEs) may account for up to two-thirds of the human genome, and as genomic threats they are subjected to epigenetic control mechanisms engaged from the earliest stages of embryonic development.

TEs are present in all organisms from bacteria to humans, and they constitute essential motors of evolution. TEs are phylogenetically and biologically related to viruses.

TEs can disrupt genes, provide novel coding activities, exert a wide range of transcriptional influences, and, because of their repetitive nature, create grounds for recombination events leading to genomic deletions and duplications, yet only a very small minority of TEs present in the human genome are still transposition-competent, accounting for one new germline integrant in 20 to 50 human births, and none is capable of horizontal transfer.

A vast majority of these DNA-binding proteins, including many of those expressed in human differentiated cells, primarily recognize sequences contained within TEs..controlling the transcriptional potential of their TE targets well beyond the early embryonic period..modulating the transcriptional impact of TE-residing sequences that are co-opted to regulate the expression of cellular genes.

A large fraction of the recognizable mobile elements in our genome are unique to humans or close relatives. The impact of this phenomenon on speciation might be particularly pronounced in organs subjected to environmental constraints that are not overly coercive, such as the brain..the central nervous system.”

The author presented evidence that the purpose of many ongoing epigenetic processes is to silence or otherwise “tame” TEs “to regulate the expression of cellular genes.” The author contrasted his view with the view that:

“Beyond this early embryonic period, TEs become permanently silenced, and that the evolutionary selection of TE controllers is the result of a simple evolutionary arms race between the host and these genetics invaders.”

http://symposium.cshlp.org/content/early/2016/01/13/sqb.2015.80.027573.long “Transposable Elements, Polydactyl Proteins, and the Genesis of Human-Specific Transcription Networks”