Literature

In a major review paper, Jacquelyn Thomas and Fazale Rana argue the critical importance of cell membranes: "Few would question if life, or at least life as we know it today, could exist without boundaries. Should the cell membrane be compromised, key processes of the cell are disrupted. Membrane formation is an essential step in the emergence of life."
Research has tended deliver "proof-of-principle" results designed to show that feasibility of membranes forming by natural processes, but there have been two omissions. The first is an integrated approach, because there are many steps involved in forming a workable membrane. The second concerns the "exacting relationship between environmental conditions and amphiphile composition and phase behaviour": "we have discovered that virtually every step in the process of membrane origins and evolution appears to be crucially influenced by environmental conditions, and lipid composition and polymorphic phase behavior. While researchers have noted the influence of these factors on the emergence of cell membranes, their pervasiveness has largely gone unrecognized."
When an overview of the research is assembled in this way, the landscape can only be described as totally fragmented: "It is almost like having 50 pieces to a puzzle and finding no two pieces fit together because they are from 50 different puzzles." When environmental factors are brought into the analysis, it is found that factors permitting some outcomes prevent others: "Proof-of-principle experiments indicate that physicochemical processes could conceivably lead to the origin and birth of cell membranes, but environmental and lipid compositional fluctuations on early Earth could hinder the emergence of cell membrane systems and the transition to contemporary cell membranes."
The conclusion of the paper is that the focus needs to be shifted towards understanding the role of environmental conditions.
Elsewhere, Rana has this to say about the research outcomes to date: "The exacting conditions needed to self-assemble and maintain biological membranes make the conclusion that these structures could emerge by natural processes improbable. At the same time, the fine-tuning and singularity of conditions needed for cell membrane structure and function stand as hallmark characteristics of Intelligent Design - reasonable expectations if God is responsible for life."

The influence of environmental conditions, lipid composition, and phase behavior on the origin of cell membranes
Jacquelyn A. Thomas and F. R. Rana
Origins of Life and Evolution of Biospheres, 2007 Jun, 37(3), 267-85 | doi 10.1007/s11084-007-9065-6

At some point in life's development, membranes formed, providing barriers between the environment and the interior of the 'cell.' This paper evaluates the research to date on the prebiotic origin of cell membranes and highlights possible areas of continuing study. A careful review of the literature uncovered unexpected factors that influence membrane evolution. The major stages in primitive membrane formation and the transition to contemporary cell membranes appear to require an exacting relationship between environmental conditions and amphiphile composition and phase behavior. Also, environmental and compositional requirements for individual stages are in some instances incompatible with one another, potentially stultifying the pathway to contemporary membranes. Previous studies in membrane evolution have noted the effects composition and environment have on membrane formation but the crucial dependence and interdependence on these two factors has not been emphasized. This review makes clear the need to focus future investigations away from proof-of-principle studies towards developing a better understanding of the roles that environmental factors and lipid composition and polymorphic phase behavior played in the origin and evolution of cell membranes.

From the conclusion: While precise membrane composition and environmental factors may be regulated in individual steps, major difficulties arise when trying to integrate the conditions essential for each step into a cohesive stepwise evolution. It is almost like having 50 pieces to a puzzle and finding no two pieces fit together because they are from 50 different puzzles. Likewise, the conditions necessary for each step of the transition from free saturated fatty acids to modern cell membranes does not "fit" together to form the completed puzzle. [snip] Proof-of-principle experiments indicate that physicochemical processes could conceivably lead to the origin and birth of cell membranes, but environmental and lipid compositional fluctuations on early Earth could hinder the emergence of cell membrane systems and the transition to contemporary cell membranes. Future investigations need to concentrate on developing a better understanding of the role that environmental conditions, and lipid composition and phase structure play in membrane origins.