An alternative approach to considering aging as a set of isolated processes in terms of discrete hallmarks, it has been suggested considering aging as involving four layers, each at a different biological scale. 187 From a general phenotype to a molecular mechanism, the suggested four layers of aging include: (i) a decline in physical function of the organism and increased susceptibility to diseases; (ii) systemic immune, metabolic, and endocrine malfunction; (iii) cellular dysfunction; and (iv) failure of biomolecule performance. 187 Failures within each layer and relations between them allegedly generate the aged phenotype and its associated susceptibility to disease.