Fruit flies and humans respond differently to retrotransposons.

Retrotransposable element insertions are 20 times more numerous per unit length of DNA in the large human genome compared to the small Drosophila genome. Whereas all Drosophila elements are subject to constant turnover (recent insertion and elimination by selection), this has not generally been the case for human retrotransposons. We suggest that a difference in recombination adopted by these organisms in response to the deleterious effects of interspersed repeated DNA can explain in part this fundamental difference between the evolutionary dynamics of fruit fly and human retrotransposons.