114 



The Journal of Heredity 



In swine l)rec(ling, too, science has 

 made slow ]jrogrcss; but as successful 

 swine breeding is easier than successful 

 sheep breeding. Germany still holds an 

 important jjlace in this field. Most of 

 the swine are in the hands of small 

 breeders, among whom there is a wide- 

 spread i^rejudice against line-breeding; 

 this leads to the constant introduction 

 of foreign blood and the rcsvilt is a fail- 

 ure of the herd to improve, or frcqucntl\- 

 an absolute deterioration of the strain. 



An example of the changes that may 

 be made by systematic breeding is 

 offered by the widespread goat industry 

 of Germany. In the last 20 years the 

 goats of the emi)ire have almost wholly 

 been changed from horned to hornless, 

 by the introduction of hornless Swiss 

 breeding stock. The same cause has 

 led to the disappearance of the old 

 colors and their supplanting by white 

 and brown. 



Turning to a consideration of the 

 formal laws of heredity, Dr. Wilsdorf 

 shows himself to be a conservative. He 

 frankl}- recognizes that most of the 

 knowledge now in the possession of 

 animal breeders on this subject is the 

 result of the research of plant breeders, 

 and he sees no objection to this state 

 of affairs, since it is now pretty generally 

 admitted that, on the whole, the laws of 

 heredity that ai)i)ly to one section of the 

 living world aj^ply to others as well. 

 He further recognizes that formal laws 

 of genetics as yet can gi\'e little real 

 hel]) to the animal ])reeder. 



MUCH YET TO BE LEARNED. 



"When the architect builds a house," 

 he writes, "he can say in advance, 'The 

 house will be like this: it will have .such 

 and such a height, such and .such a 

 shajjc,' and so on. The gardener who 

 has to lay out a garden or jiark can tell 

 in advance just how the result of his 

 work will kx)k. He jjicks out the jjlaccs 

 where the paths will run, where turf 

 will be ]jlanted, where flowers will 

 appear; and he can say to himself, 'In 

 this jjlace such and such a tree will 

 grow.' Architect and gardener alike 

 know beforehand how the finished 

 I)r()duct of their work will U)ok; but not 

 so the animal breeder. lie is dealing 



with laws of nature which are not yet 

 w^ell enough known to enable him to 

 predict with absolute certainty how 

 they will work. One knows well 

 enough that the offspring of two parents 

 usually is like them, but whether it will 

 more resemble the father or the mother 

 can not with certainty be foretold. 

 Exactly in this uncertainty lies the 

 difficulty of the animal breeder's work. 

 It has therefore long been the aim of 

 experimental breeding and jmrticularly 

 of experiments in hybridization, to find 

 certain rules with which heredity com- 

 ])lics. We are well aware that there are 

 animals which transmit their character- 

 istics with unusual prejjotency, and we 

 can say with a good deal of certainty 

 that the product of most of these 

 animals w^ill have a large proportion of 

 those characteristics. But frequently 

 enough comes a case where we are 

 deceived, and the number of cases in 

 which we can speak of a 'rule' is pro- 

 portionately ^'ery small : the part of the 

 breeding industry in which we still 

 walk in uncertainty is much larger than 

 that in which we can ad\-ancc without 

 groping. 



"The .search for these rules, how- 

 ever, has occupied a great number of 

 naturalists during recent years, and 

 still occupies them. The work hitherto 

 accom]jlished is a great one and, even 

 if the goal is still a long distance ahead, 

 we have nevertheless taken a big step 

 forward. Plate distinguishes four dif- 

 ferent methods of heredity, as follows: 



1. Mosaic heredity. 



2. Blending or intermediate heredity. 



3. Mutational heredity. 



4. Alternative, segregating or Mende- 



lian heredity. 

 "In mosaic heredit\- the characters 

 of the i^arents exist side by side in the 

 offs])ring — as in a mosaic. As example 

 I may cite the l)arred progen>' of white 

 and black fowls bred Ijy Davenjjort; or 

 the color of the well-known Blue 

 Andalusian fowl, where the pigments 

 black and white, intimately mixed, 

 produce an ai)paront blue color. Hilz- 

 heimer cites the Baldinger Tiger Swine 

 as an example of this sort of heredity: it 

 was ])roduced by crossing the white 

 native race with the black Berkshire. 



