And so we see that this is precisely what prevents the asymmetry from being lost. So the membrane asymmetry is preserved over long periods of time, because membrane proteins do not actually rotate from one side of the membrane to the other side of the membrane, because this is too energetically unfavorable. Now, in addition, what also retains or preserves the asymmetry of the membrane is the fact that membranes are always constructed from preexisting membranes, and those preexisting membranes are always asymmetric. So, in the same way that to actually create a cell, we have to begin with a cell, to create a membrane, we have to begin with the membrane. So when we're building our cell membrane, we build it by essentially expanding the preexisting membrane. And that preexisting membrane basically was asymmetric to begin with.