ON THE MEALY LINNET. 
457 
those of our native bird, even allowing for a moderate degree of variance more 
than is observable—the birds themselves appear to be quite undistinguishable. 
We have now seen each character, in its turn, stand forth as the sole exception 
to complete resemblance, though reduced to the very minimum of non-conformity; 
and this in races inhabiting the same districts, as well as in those which people 
different parts of the globe,—thus negativing the assumption that external 
influence had necessarily produced the diversity, which theory obviously requires 
for its support the existence of intermediate specimens in all their progressive 
stages, and is consequently inconsistent with the observed permanency of the 
various races in question. At the same time, as I have remarked on a former 
occasion, although these closely-allied races, when inhabiting the same locality, 
apparently manifest no disposition to intermix and blend, as is uniformly the 
case with even the most distant of true varieties, such as are caused by domes¬ 
tication—and it may be that many such races constantly keep apart, even though 
so similar that we possess no means of distinguishing them—yet that, in the 
case of an occasional union (brought about by peculiar circumstances), it is highly 
probable that the tendency to barrenness in the mule progeny would decrease 
in the ratio of the amount of physiological affinity subsisting between the parents, 
until in the most approximate races (though not descended from a common origin, 
and therefore specifically distinct) the hybrid offspring would be even mutually 
as prolific as individuals of unstained descent. In connexion with this specula¬ 
tion, the highly curious physiological fact may be borne in mind—which possibly 
may have for its object the continued separate existence of each' primitive 
race—that very closely-allied species, and (as an apparent consequence of the 
same law) similar varieties also, less frequently produce, on intermixture, offspring 
of blended character, than progeny entirely resembling one or the other parent. 
However, having launched into conjecture, it may, on the other hand, be sup¬ 
posed, as perfectly consistent with this presumed law, adjudged to regulate the 
productiveness of hybrids, that the aversion to interbreed would lessen with each 
additional degree of affinity; till in the most approximate races of all, though 
still not descended from the same original parentage, all mutual unwillingness to 
reproduce would be entirely extinguished,—so that, in a few generations, nothing 
Vfould prevent their becoming effectually blended, save that inexplicable tendency 
(so remarkably evinced by even emigrants) to return to pair and propagate in the 
native locality, which must necessarily occasion relatives to transmit their race in 
far greater proportion than individuals of diverse lineage,—a circumstance which 
it is truly surprising does not induce a much greater splitting into varieties than 
is actually observed; and this, if climate or locality really exercised the amount 
of influence whicli many naturalists imagine, would confer distinctive characters 
on the individuals of almost every province. 
