Lego principle

The Lego principle is an informal name for the notion that life is made up of a relatively small set of molecules, and life undergoes selective pressure toward manufacturing them, as doing so contributes to its own survival and proliferation. The small set consists of molecules usable for the microscopic processes life carries out, as well as molecules from which complex structures and machinery can be assembled. Its limited count allows various life forms to interact. Thus, the presence of life skews molecular abundances from the distributions that occur in the absence of life. So while the presence of some substance that does not occur abiotically constitutes a type of biosignature, another type of signature is a distribution of molecular abundances that cannot be explained through abiotic processes. Earth life consists of several amino acids, nucleotides, sugars, and lipids, and Earth life's cellular manufacturing processes add to the supply of many of these.