The answer is genetic drift.
Archaea bacteria live and thrive in extreme environments (extreme salt, extreme temperature), whereas eubacteria live best in more 'normal' environments that are closer to what we (humans) are used to.
The similarity between directional and disruptive is that both are types of selection on polygenic traits in which the curve shift away from the middle.
The different between disruptive and directional is in disruptive move toward both ends . And in directional, the curve shift toward one end.
Slows the flow of water traveling
