Studies on inbreeding. I. The effects in inbreeding on the growth and variability in the body weight of the albino rat

The rapid development of the new science of genetics has opened up many fertile fields of investigation and it has also revived interest in the problem of inbreeding which has been dormant for many years.Charles Darwin ('75, '78) considered the subject of inbreeding so important that not only did he collect all available data regarding it, but he himself carried on a series of inbreeding experiments that extended over a period of eleven years.Darwin's experiments on plants were followed by those of Crampe ('83), of Huth ('87), and of Retzima-Bos ('93; '94) on various species of mammals.The conclusions reached by each of these investigators can well be stated in the words of Darwin ('78) : "The consequences of close interbreeding carried on for too long a time, are, as is generally believed, loss of size, constitutional vigor and fertility, sometimes accompanied by a tendency to malformation."Darwin adds, furthermore : "That any evil directly follows from the closest interbreeding has been denied by many persons, but rarely by any practical breeder andnever, as far as I know, by one who has largely bred animals which propagate their kind quickly."On account of the almost universal prejudice against inbreeding, or because the results of former work seemed conclusive, the problem of inbreeding was practically ignored by scientists after the publication of Retzima-Bos' results in 1593, and only within the past decade has it again received any serious consideration.The recent experiments of Gentry ('05) on swine, of Castle et al. ('06) and of Moenkhaus ('11) on Drosophila, and