the first cell membranes are thought to have self-assembled from simple, single-chain lipids synthesized in the environment (Budin I, Szostak JW. "Physical effects underlying the transition from primitive to modern cell membranes")
According to Budin and Szostak, low levels of phospholipids drove membrane growth. Decreasing fatty acids then increase phospholipids. this synthesizing is advantageous in competing for early stage lipids and opens new avenues of selectivity.