Much of the recent stimulus to the study of the Science of Breeding was occasioned by the discovery of Mendel's Law. Briefly, the law states that when two pure traits or characters are crossed, one dominates in the first generation of offspring—the other remaining hidden or recessive. Of the second generation, one-half the individuals are still mixed, bearing the dominant characteristic externally and the other hidden; one-fourth are pure dominants and one-fourth are pure recessives. In future generations the mixed or hybrid individuals again give birth to mixed and pure types apportioned as before, thus continuing until all offspring become ultimately pure. For illustration: If rose and single comb chickens are crossed, rose combs are dominant. The first generation will all have rose combs. The second generation will have one-fourth single combs that will breed true, one-fourth rose combs that will breed rose combs only, and one-half that again will give all three types.
Mendel's Law works all right in cases where pure unit characteristics are to be found. For the great practical problems in inheritance, Mendel's law is utterly hopeless. The trouble is that the chief things with which we are concerned are not unit characteristics but are combinations of countless characteristics which cannot be seen or known, hence cannot be picked out. Thus the tendency to revert to pure types is foiled by the constant recrossing of these types.
Mendel's law is a scientific curiosity like the aeroplane. It may some day be more than a curiosity, but both have tremendous odds to overcome before they supplant our present methods.
Prof. C.B. Davenport, of the Carnegie Institute, is working on experimental poultry breeding in its purely scientific sense. His conclusions have been much criticised by poultry fanciers. The truth of the matter is that the fancier fails to appreciate the spirit of pure science. The scientist, enthused to find his white fowl re-occur after a generation of black ones, is wholly undisturbed by the fact that the white ones, if exhibited, might be taken for a Silver Spangled Hamburg.
Mendel's law as yet offers little to the fancier and less to the commercial poultryman. Its study is all right in its place, but its place is not on the poultry plant whose profits are to buy the baby a new dress.
Breeding for Egg Production.
Attempts to improve the egg-producing qualities of the hen date from the domestication of the hen, but it has only been within the last few years that rapid progress has been possible in this work. The inability to determine the good layers has been the difficulty.
The great majority of people make no selection of hens from which to hatch their stock. The eggs of the whole flock are kept together and when eggs are desired for hatching they are selected from a general basket. It has been assumed, and is shown by trap-nest records, that eggs thus selected in the spring of the year are from the poorer, rather than from the better layers. This is because hens that have not been laying during the winter will lay very heavily during the spring season. Many breeders have attempted to pick out the good layers by the appearance of the hens. Before the advent of the trap-nest the "egg type" of hen was believed to be a positive indication of a good layer. The "egg type" hen had slender neck, small head, long, deep body of a wedge shape. Various "systems" founded on these or other "signs" have been sold for fancy prices to people who were easily separated from their money. Trap-nest records show such systems to be on a par with the lunar guidance in agricultural operations.
I might remark here that the determination of sex by the shape of the egg or similar methods, is in a like category. Science finds no proof of such theories.
A few methods of selecting the layers have been suggested which, while far from absolute, are of some significance and are well worth noting. The hen that sits upon the roost while other hens are out foraging, is probably a drone. The excessively fat or the excessively lean hens are not likely to be layers. It would naturally be supposed that the active laying hen would be the last one to go to roost at night. At the Kansas Experiment Station, the writer made observations upon the order in which the hens went to roost, and the above assumption was found in the majority of cases to be correct.