Page:The Annual Register 1899.djvu/537

 1899.] SCIENCE. 113

organs are affected ; and that, of any change in them, nothing is certainly known beyond the production on the one hand of sterility, and on the other of an increase in genetic variability. It might seem that sufficient attention has not yet been paid to the action of altered conditions upon growth. A changed environment that has wrought no effect upon the parents' organs of reproduction may nevertheless act energetically upon those organs in the offspring during the periods of gestation and adolescence.

Professor Pearson has proved that fertility and fecundity are herit- able characters, and has established the probability that they follow the Galtonian rule.

Lord Morton's celebrated " infection " experiment has acquired new interest. A chestnut Arab mare that had been successfully crossed with a quagga subsequently produced to a black Arab horse a succession of striped foals.

Professor Ewart has cast this case into the crucible and it has not stood the test. The foals were not more striped than are many others that have had no quagga intermixture. They are all, in his opinion, examples rather of reversion or atavism than of telegony or "throw- back." And he considers that telegony is more likely to exhibit itself in the offspring's throwing back to an ancestor of the dam than to a previous mate. Atavism, on the contrary, is reversion to an older type. This often happens in crossings, and would occur more frequently in ordinary cases than it does were it not prevented by inbreeding, which is the chief means of establishing prepotency.

Professor Ewart's experiments have shed a brilliant light on the whole subject. He had observed that mules and hinnies were often richly striped and sometimes possessed a more ancestral colour than their parents. His zebra-horse hybrids, or zebrules, and his horse-zebra hybrids, or zebrinnies, are not marked like their Burchell-zebra parent, but resemble in both cases the Somali zebra, which is the most primitive of all its kind.

As for man, he escapes one evil only to encounter another. He may now, indeed, marry a widow with a family and no longer fear that his children will have more likeness to the first hushand than to himself ; but in any remote exogamy, in any outlandish alliance, he must reckon with the possibility that his offspring will revert to a byegone strain, to a type incompletely adapted to present conditions.

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