Phospholipids will form a bilayer in water because they contain hydrophobic (Water fearing.. in this cause water "hating") tails and hydrophilic heads (water loving). So they form a bilayer to remove the tails from water likewise, this satisfies the hydrophilic heads because they are still exposed to water.
It is a type of reproductive barrier that can lead to speciation. Behavioral behavior, such as mating rituals as in when two populations of the same species show some difference in behavior, typically in mating rituals
