The "mobile bricks" of human evolution: how transposable elements shaped human phenotypes

Far from being "junk" and devoid of function, transposable elements have been identified as players in genomes evolution and regulation, and are also used as valuable genetic markers to study population differentiation. Here we present a detailed review on how transposons participated in human evolution: from adaptation to extreme environments and response to both internal and external stressors, to phenotypes directly emerging from transposon mobilization activities. We dedicate a section to brain plasticity and neuronal differentiation, highlighting the possible role of transposable elements in neuro-psychiatric disorders in the context of emerging hypotheses such as the genomic trade-off and price-to-pay. Furthermore, we discuss methods and approaches to study the influence of transposable elements on human evolution, covering challenges to include ancient DNA in these studies. To conclude, we propose that transposons are not mere "background noise" in host genomes, but that they can be seen as genetic regulators of human phenotypes.