he result is fortuitous. It is not
clear in the original to how much of the passage the two ? refer.

Before considering difficulties of theory of selection let us consider
character of the races produced, as now explained, by nature. Conditions
have varied slowly and the organisms best adapted in their whole course
of life to the changed conditions have always been selected,--man
selects small dog and afterwards gives it profusion of food,--selects a
long-backed and short-legged breed and gives it no particular exercise
to suit this function &c. &c. In ordinary cases nature has not allowed
her race to be contaminated with a cross of another race, and
agriculturists know how difficult they find always to prevent
this,--effect would be trueness. This character and sterility when
crossed, and generally a greater amount of difference, are two main
features, which distinguish domestic races from species.

[Sterility not universal admitted by all{65}. _Gladiolus_, _Crinum_,
_Calceolaria_{66} must be species if there be such a thing. Races of
dogs and oxen: but certainly very general; indeed a gradation of
sterility most perfect{67} very general. Some nearest species will not
cross (crocus, some heath <?>), some genera cross readily (fowls{68} and
grouse, peacock &c.). Hybrids no ways monstrous quite perfect except
secretions{69} hence even the mule has bred,--character of sterility,
especially a few years ago <?> thought very much more universal than it now
is, has been thought the distinguishing character; indeed it is obvious
if all forms freely crossed, nature would be a chaos. But the very
gradation of the character, even if it always existed in some degree
which it does not, renders it impossible as marks <?> those <?> suppose
distinct as species{70}]. Will analogy throw any light on the fact of
the supposed races of nature being sterile, though none of the domestic
ones are? Mr Herbert <and> Koelreuter have shown external differences will
not guide one in knowing whether hybrids will be fertile or not, but the
chief circumstance is constitutional differences{71}, such as being
adapted to different climate or soil, differences which [must] probably
affect the whole body of the organism and not any one part. Now wild
animals, taken out of their natural conditions, seldom breed. I do not
refer to shows or to Zoological Societies where many animals unite, but
<do not?> breed, and others will never unite, but to wild a