LECTURE XXVI 



GERMINAL SELECTION {continued) 



Germinal selection, spontaneous and induced — Climatic forms of Polyommatus phlceas 

 — Deformities — Excessive augmentation of variations — Can it lead to the elimination 

 of a species? — Saltatory variations, copi)er-beech, weeping trees — Origin of sexual 

 distinguishing characters — Formation of breeds among domesticated animals — 

 Degenerate jaws — Human teeth — Short-sightedness — Milk-glands — Small hands and 

 feet — Ascending variation — Talents, intellect — Combination of mental endowments — 

 The ultimate roots of heritable variation — There are only plus- and minus- variations — 

 Relations of the determinants to their determinates — The play of forces in the 

 determinant system of the id — Germinal selection inhibited by personal selection — 

 Objection on the score of the minuteness of the substance of the germ-plasm. 



HiTHEKTO we have derived the variations of the determinants 

 of the germ-plasm, upon which we based the process of germinal 

 selection, from chance local fluctuations in imtrition, such as must 

 occur in an individual id, independently of the nutrition of the other 

 ids of the same germ-plasm. But there are doubtless also influences 

 which set up similar nutritive changes in all ids, and by which, 

 therefore, all homologous determinants, in as far as they are sensitive 

 to the nutritive change in question, are affected in the same manner. 

 To this category belong changes in the external conditions of life, 

 and particularly climatic changes. It is, then, germinal selection 

 alone which brings about the presence of a majority of ids with 

 determinants ^'arying in the same direction, and personal selection 

 has no part in the transformation of the sj^ecies. Many years ago 

 I instituted experiments with a small butterfly, Pararga egeria, 

 and these showed that a heightened temperature so influenced the 

 pupai of this form that the butterflies emerged with a different 

 and deeper yellow ground-colour, similar to that of the long-known 

 southern variety Meione. More thoroughly decisive, however, were 

 the experiments on Polyominiatus jMceas, the small ' fire-buttei-fly,' 

 which were carried on in the eighties by Merrifield in England and 

 by myself almost at the same time. I shall discuss these later in 

 more detail, and will only say here that this butterfly, whose range 

 extends from Lapland to Sicily, occurs in two forms, the southern 

 distinguished by a 'dusting' of deep black from the northern, in 

 which the wing-surfaces are of a pure red-gold. The experiments 



