Inhaltsangabe
This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1887 edition. Excerpt: ...years, even if occupying the same districts and breeding at exactly the same season, interbreeding could occur between the two forms only once in 221 years, or once in 13 generations of the longer lived race, and once in 17 generations of the shorter lived race. During the year 1885 the two races appeared simultaneously. The opportunity for testing whether they would freely interbreed if brought together has, therefore, passed not to return till the year 2106; but the distribution of the two races in different districts seems to indicate that Local Segregation has had an important influence in the development of the race. It is manifest, however, that if during a period of local separation, or if during the period of 221 years of Cyclical separation after the thirteen-year race was first formed, this race should become modified in the season of its appearing, there would after that be no mingling of race, though brought together in the same districts. This would be Seasonal Segregation, which we shall consider in the next section; but what is of special interest here, as an example of complete Cyclical Segregation, is the fact that at Fall River, Massachusetts, there is a brood of the seplemdecim form, due a year later than the universal time of appeariug. In any species where the breeding of each successive generation is separated by an exact measure of time which is very rigidly regulated by the constitution of the species, Cyclical Segregation will follow, if, through some extraordinary combination of circumstances, members sufficient to propagate the species are either hastened or delayed in their development, and thus thrown out of synchronal compatibility with the rest of the species. If, after being retarded or hastened in...
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