INTER VS INTRA. “Gene transfer within species should slow down diversification by increasing genetic similarity. This may result in higher standing stocks of (more or less) identical genomes and thus in a higher survival chance depending on the stability of the environment. Gene transfer across species and genus barriers should promote adaptation and increase diversity.”
http://onlinelibrary.wiley.com/doi/10.1046/j.1462-2920.2003.00539.x/full