Table 1: Categories of HGTs leading to innovation and complexity.

Type “Beneficial” HGTs “Neutral” HGTs “Parasitic” HGTs Definition HGTs that provide an initial selective advantage to the recipient HGTs are maintained by random genetic drift HGTs do not provide an initial selective advantage to the recipient but over time may adapt to have a beneficial function or be maintained via pathways to neutral complexity in the recipient Examples (i) Metabolic pathway expansion and invention (i) Many ORFan genes and genes of limited distribution and with unknown function may be in this category [14, 15] (i) Inteins (ii) Group I Introns (iii) Group II Introns (ii) Adaptation to new ecological niches