Man's Place in Nature

Abstract

SPECIALIZATION is not in itself any proof of advance, yet both in the domain of mind and that of organic life the term is constantly used as though it carried with it the idea of progress, instead of, as is the fact, a mingling of advance with retrogression, the upward or downward tendency of which can only be determined by a careful comparison of all the factors. In all evolution, organic or super-organic, specialization commences at. the bottom of the scale, and a higher grade is only attained by a longer continuance in a generalized condition before specialization-a continuance during which, not some special part but the entire organism becomes capable of wider activities. As the upward development proceeds, branches break off, become specialized, and perfect or complete themselves, that is, become incapacitated for further development. The real line of advance is not to be sought for in the specialized offshoot, but in the growing stem from which it parted. To give examples from the Vertebrata; it is not the highly specialized teleostean fish, such as the perch, that is in the line of advance, but the more generalized ganoids and Dipnoi through which the upward line runs on into the Batrachia; neither is it the highly specialized flying pterodactyl that is in the line of advance from reptile to bird or mammal; nor can the line of mammalian descent be traced through the birds, in which, high though the type is, specialization of some parts, accompanied by atrophy of others, has resulted in organic completeness at a level lower than that which has been reached by the summit of the mammalian stem. The highest specialization is that based upon perfection of the