The Descent of Man

do would be to persevere in selecting every
male pigeon which was in the least degree of a
paler blue; and the natural result of this process,
if steadily carried on for a long time, and if
the pale variations were strongly inherited or
often recurred, would be to make his whole
stock of a lighter blue. But our fancier would be
compelled to match, generation after generation,
his pale blue males with slaty females, for
he wishes to keep the latter of this colour. The
result would generally be the production either
of a mongrel piebald lot, or more probably the
speedy and complete loss of the pale-blue tint;
for the primordial slaty colour would be transmitted
with prepotent force. Supposing, however,
that some pale-blue males and slaty females
were produced during each successive generation,
and were always crossed together,
then the slaty females would have, if I may use
the expression, much blue blood in their veins,
for their fathers, grandfathers, etc., will all have
been blue birds. Under these circumstances it is