A moment’s reflection will bring to light the preliminary flaw of incomplete enumeration of possibilities. To suppose that inheritance alone can account for structural resemblance is an unwarranted assumption. Without a doubt, there are other similifying influences at work in Nature besides inheritance. True, inheritance is one possible explanation of the similarity of organisms, but it is not the _only_ one. Even among the chemical elements of inorganic nature we find analogous uniformities or “family traits,” which, in the absence of any reproductive process whatever, we cannot possibly attribute to inheritance. Mendeléeff’s discovery of the periodicity of the elements, arranged in the order of their atomic weights, is well-known. At each interval of an octave, a succession of chemical types, similar to those of the preceding octave, recur. Hence elements appearing in the same vertical column of the Periodic Table have many properties in common and exhibit what may be called a family resemblance. Now, we have in the process of atomic disintegration, as observed in radioactive elements and interpreted by the electronic theory of atomic structure, a reasonably satisfactory basis upon which to account for the existence of these inorganic uniformities. Here analogous chemical constitution, produced in accordance with a general law, results in uniformity that implies a similar, rather than an identical, cause. The hypothesis of parallelistic derivation from similar independent origins accounts quite as well for the observed uniformities as does the hypothesis of divergent derivation from a single common origin. Why, then, should we lean so heavily on the already overtaxed principle of inheritance, when parallelism is as much a possibility in the organic world as it is an actuality in the inorganic world?