256 THE SCIENTIFIC MONTELT
♦
results of the actual breeding experiments agree closely with the cal- culated ezpectationa.
Such extensive use of the unit-factor hypothesis has been made that in the graphic language of the day an organism is sometimes de- picted as a bundle of separate qualities^ of so-oalled unit^haracters, each the outcome in mechanical fashion of a single discrete germinal cause, which does not vary and which is self propagative. Viewed in this artificial light, biology assumes a rigid appearance far from itB real nature, its task appearing twofold, to discover through cross breed-' ing the elementary or unit characters of organisms and the laws govern- ing their combination.
It should be said that such a conclusion is implied rather than positively stated in the writings I have in mind, and is expressly con- demned by some prominent students of Mendelian heredity (T. H. Morgan). The facts of paleontology, anatomy and development dem- onstrate how artificial it is, for they show that every part and process varies among the individuals of any one tune, and the mode or lypical condition changes from age to age. Moreover, the parts of ihe body are so interconnected materially and their activities or functions are so interassociated, that to speak of the body as a group of units is mis- leading. It is to misuse the license that is only allowed in ellegoiy, or in science for the purpose of facilitating description. A tiled floor is composed of pieces which can be taken apart and recombined. But an organism, Olivia for instance, is not a mosaic, for the items in her inventory, as "two lips indifferent red, two grey eyes with lids to them '^ are not separate and independent components. The essential fea- tures of an organism appear to be as closely associated, fully as insep- arablei, as are the comers, cleavage, color and lustre of a crystal, of cal- cite, for example. For given the right conditions, the germ cell or other regenerative mass will always produce them.
I hasten to remind you that unit-character in technical studies on Mendelian heredity has a definite meaning, referring to the class of differential features, which mark off the individuals of a race, or of allied races, one from the other. Such would be the color of the eye perhaps, or the fulness and curve of the lip. It is, as already said, these contrajsting features in respect to which the two parents differ, which behave independently of one another and which may therefore be recombined in various ways.
The question as to the permanency of such characters in hereditary lines is interesting to all of us. There is no doubt that they are re- markably constant and persistent, but experimental breeding amply demonstrates that they are subject to the sudden changes known as mutations. It has also been demonstrated that in the course of selec- tive breeding they undergo change (W. E. Castle). They show then, as do the many series of intergrading organisms, that the rule of heredity over living things is not absolute. Living things, in fact.
�� �
