50 MESSRS. C. DAHWIN and a. WALLACE ON THE 



(that is, if the check to increase fell chiefly on the seeds), those 

 seeds which were provided with ever so little more down, would 

 in the long run be most disseminated ; hence a greater number of 

 seeds thus formed would germinate, and would tend to produce 

 plants inheriting the slightly better-adapted down*. 



Besides this natural means of selection, by which those indi- 

 viduals are preserved, whether in their egg^ or larval, or mature 

 state, which are best adapted to the place they fill in nature, 

 there is a second agency at work in most unisexual animals, 

 tending to produce the same effect, namely, the struggle of the 

 males for the females. These struggles are generally decided 

 by the law of battle, but in the case of birds, apparently, by the 

 charms of their song, by their beauty or their power of court- 

 ship, as in the dancing rock-thrush of G-uiana. The most vigor- 

 ous and healthy males, implying perfect adaptation, must gene- 

 rally gain the victory in their contests. This kind of selection, 

 however, is less rigorous than the other ; it does not require the 

 death of the less successful, but gives to them fewer descendants. 

 The struggle falls, moreover, at a time of year when food is gene- 

 rally abundant, and perhaps the effect chiefly produced would be 

 the modification of the secondary sexual characters, which are not 

 related to the power of obtaining food, or to defence from enemies, 

 but to fighting with or rivalling other males. The result of this 

 struggle amongst the males may be compared in some respects 

 to that produced by those agriculturists who pay less attention 

 to the careful selection of all their young animals, and more to 

 the occasional use of a choice mate. 



II. Abstract of a Letter from C. Darwin, Esq., to Prof. AsA Gray, 

 Boston, U.S., dated Down, September 5th, 1857. 



1. It is wonderful what the principle of selection by man, that is 

 the picking out of individuals with any desired quality, and breed- 

 ing from them, and again picking out, can do. Even breeders have 

 been astounded at their own results. They can act on difterences 

 inappreciable to an uneducated eye. Selection has been methodi- 

 cally followed in Europe for only the last half centuiy ; but it 

 was occasionally, and even in some degree methodically, fol- 

 lowed in the most ancient times. There must have been also 

 a kind of unconscious selection from a remote period, namely in 



* I can see no more difficulty in this, than in the planter improving his 

 rarieties of the cotton plant. — 0. D. 1858. 



