"... we need to put everything into an evolutionary framework, simply because complexity arises in biological systems by accretion and modification and not by reinvention. Thus, the properties of many of the components in our cells, whether these are mRNAs or proteins, will be conditioned not only by processes of selection for specified activities and levels because these are positively required but may also take up any value because there are no negative consequences for the organism. This ‘don't care’ condition will almost certainly be present because it is a cheap solution to the regulation problem of complex systems. Thus a 20% or a twofold increase, or indeed the very presence, of a protein may be very significant or totally irrelevant depending on whether it is following a ‘don't care’ condition. Only experiment can decide that."