In the first place there is an increasing delicacy of constitution; the growing fineness of limb and structure end, after a few generations, in fragility.  Overbred animals have little stamina; they resemble in this respect the “weedy” colts so often reared from first-class racers.  One can perhaps see in a general way why this should be so.  Each individual is the outcome of a vast number of organic elements of the most various species, just as some nation might be the outcome of a vast number of castes of individuals, each caste monopolising a special pursuit.  Banish a number of the humbler castes—­the bakers, the bricklayers, and the smiths, and the nation would soon come to grief.  This is what is done in high breeding; certain qualities are bred for, and the rest are diminished as far as possible, but they cannot be dispensed with entirely.

The next difficulty lies in the diminished fertility of highly-bred animals.  It is not improbable that its cause is of the same character as that of the delicacy of their constitution.  Together with infertility is combined some degree of sexual indifference, or when passion is shown, it is not unfrequently for some specimen of a coarser type.  This is certainly the case with horses and with dogs.

It will be easily understood that these difficulties, which are so formidable in the case of plants and animals, which we can mate as we please and destroy when we please, would make the maintenance of a highly-selected breed of men an impossibility.

Whenever a low race is preserved under conditions of life that exact a high level of efficiency, it must be subjected to rigorous selection.  The few best specimens of that race can alone be allowed to become parents, and not many of their descendants can be allowed to live.  On the other hand, if a higher race be substituted for the low one, all this terrible misery disappears.  The most merciful form of what I ventured to call “eugenics” would consist in watching for the indications of superior strains or races, and in so favouring them that their progeny shall outnumber and gradually replace that of the old one.  Such strains are of no infrequent occurrence.  It is easy to specify families who are characterised by strong resemblances, and whose features and character are usually prepotent over those of their wives or husbands in their joint offspring, and who are at the same time as prolific as the average of their class.  These strains can be conveniently studied in the families of exiles, which, for obvious reasons, are easy to trace in their various branches.

The debt that most countries owe to the race of men whom they received from one another as immigrants, whether leaving their native country of their own free will, or as exiles on political or religious grounds, has been often pointed out, and may, I think, be accounted for as follows:—­The fact of a man leaving his compatriots, or so irritating them that they compel him to go, is fair evidence that