THE INTRODUCED SPARROW. 3 



In 1850 the first house sparrows of Europe were introduced 

 into this country, and from that time to 1870 upwards of 1500 

 birds are said to have been brought from the Old World (Mer- 

 riam-Barrows, '89). To these introduced birds the environment 

 has been novel. They have found abundant food, convenient 

 and safe nesting places, practically no natural enemies, and 

 unrivaled means of dispersal. Aside from an early and brief 

 period of fostering care, they have been left to shift for them- 

 selves; natural agencies have since been at work, and in the 

 relatively short space of forty years a continent has been, not 

 merely invaded, but inundated by an animal which, in its native 

 habitat, has been fairly subservient to the regulations imposed 

 by competing life. 



It seems to the speaker that here is an excellent example of 

 the suspension of natural selection, for here, at least as far as 

 certain external factors of selection are concerned, Nature does 

 not select. Nearly all the young birds reach maturity; varia- 

 tions in color and structure, unless most extreme, are appar- 

 ently not disadvantageous to their possessor; and if these 

 variations are heritable, they do not seriously handicap the indi- 

 viduals of the next generation. A considerable departure in 

 nesting and breeding habits does not jeopardize the domestic 

 interests, and the simple mode of life permits even the weak 

 individuals to endure. We conclude, then, that there is evi- 

 dence to prove the first proposition, viz., in a specific case and 

 in respect to certain characters, the operation of natural selec- 

 tion has been suspended. 



For a proper discussion of propositions 2, 3, and 4, it was my 

 first purpose to collect a large number of the American birds 

 and compare them directly with an equal number collected in 

 England; but the labor and expense involved made this pro- 

 cedure inexpedient. The Qgg of the bird, however, is easy 

 to secure, readily preserved, and can be purchased from Euro- 

 pean dealers for a relatively small price. It presents a remark- 

 able range of variation, both in shape, size, and color, and offers 

 certain fixed and readily measurable features which are not 

 presented by the bird itself. Moreover, my observations lead 



