WHAT IS AN ORGANISM? 1/9 



tional activity of growth and development will go on normally 

 at the expense of change of morphological form. 



Normal Growth. This explanation assumes that there is a 

 normal growth, and the determining of what is normal to 

 each individual is found in the ancestry; i.e., at the outset of 

 embryonic growth the normal function of the development of 

 the individual is already determined. This includes the attain- 

 ment of the morphological and the physiological characters of 

 the class, order, family, genus, and species to which the 

 organism belongs. The egg at the first appearance of the 

 embryo is determined not only to be a vertebrate, but a bird, 

 of the order Rasores, of the suborder Gallinae, of the family 

 Phasianidae, of the genus Gallus, and of one of the many 

 varieties of the species Gallus domesticus. Such is the normal 

 development for that particular embryo. The laws of the 

 development in its every step may be studied, and have been 

 very fully traced in this particular case, and the knowledge of 

 the law is based upon the observed order of these steps in the 

 development ; the inference which we naturally draw is that 

 every new development of a similar egg will be the same. 



Natural Selection, as an explanation of the changes which 

 transpire in phylogenesis, assumes that the slight adjustments 

 of the morphological characters, which take place in the onto- 

 genesis of the individual, are added to the determining factors 

 of development for the next generation ; that adjustments 

 which are very slight in each case, by accumulation from 

 generation to generation, bring about the differences which 

 distinguish the various species, genera, families and orders of 

 the classes of the animal kingdom. And this is what is 

 meant by " descent with modification." Instead of the idea 

 of descent along a uniform line, in which the offspring differs 

 in only unimportant and strictly variable characters from any 

 of its ancestors, the school of Darwin holds that the slight 

 variations observed (between the offspring and parent, or 

 among the offspring of a common parentage) do not tend to 

 become less in succeeding generations, but that the variations 

 have unequal values in relation to the advantage of the in- 

 dividual ; and in the struggle of individuals for life, those 

 individuals possessing the slightest advantage over their fel- 



