The earliest cells were created when self-replicating molecules called ribonucleic acids (RNA) were enveloped in a membrane called a phospholipid bilayer, which is still the basis for all modern human cell membranes. This bilayer protected the RNA from the harsh outside environment, allowing self-replication. These early cells lived in a sea of nutrients, obtaining food and energy directly from their environment. As long as nutrients were available, they survived, but they were always on the edge of extinction. The prime directive of life, even at this early stage of evolution, was to
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