236 Biology in America 



pirafTe, by its lofty stature, inucli elongated neek, fore legs, 

 head and tongue, has its whole frame beautifully' adapted for 

 bi'owsing on the higher braneiics of trees. It can thus ob- 

 tain food beyond the reach of the other , . . hoofed animals 

 iidiabiting the same country, and this must be a great advan- 

 tage to it during dearths. ... So under nature with the nas- 

 cent giratfe, the individuals which were the highest browsers 

 and were able during dearths to reach even an inch or two 

 above the others (variation) will often have been preserved 

 (selection). , . . They will have intercrossed and left off- 

 spring, either inheriting the same bodily peculiarities, or with 

 a tendency to vary again in the same manner (inheritance) ; 

 whilst the individuals, less favored in the same respects, will 

 have been the most liable to perish."^ 



One of the strongest evidences cited by Darwin in support 

 of his theory was that of artificial selection. If man, he said, 

 in a few hundreds or at most thousands of j^ears, could pro- 

 duce, by selection, all the manifold varieties of domestic plants 

 and animals which we know today, why could not Nature, 

 working through the countless ages of biologic time, perform 

 the creative wonders of the past and present kingdoms of ani- 

 mals and plants inhabiting the world? It is difficult however 

 to subject the work of the practical breeder to scientific 

 analj'sis, based as it is upon purely economic grounds. Fur- 

 thermore, we have today a mass of information regarding in- 

 heritance which was not available to Darwin. Within re- 

 cent years therefore the problem has been attacked scien- 

 tifically by a number of workers, the pioneer being the Dan- 

 ish liotanist, Johannsen. 



If one choose any group of organisms, be they men or be 

 they microbes, and carefully aiTange them according to size, 

 he will find that they form a series, with an average and 

 two extremes — a greater and a lesser. If now, on the one 

 hand, the largest individuals, and on the other the smallest, 

 be chosen for breeding, and from their offspring in turn the 

 largest and the smallest be again selected, can finally two new 

 races, a larger and a smaller, be developed? This question 

 forms the crux of the selection theory. 



To test it Professor Johannsen of Copenhagen chose at ran- 

 dom 12,000 beans and measured the length and breadth of 

 eacli to obtain an average. From these he chose nineteen, rang- 

 ing from the largest to the smallest. Breeding these for seven 

 years, and selecting the largest and smallest seeds for each 

 planting, he found that, while the largest beans produced 

 seed larger than the average of the 12,000, and the smallest 

 produced seed smaller than the average, bubsequent selection 

 » Pp. 276-7, 6th ed. 



