widely diffused species?

1) Does "widely diffused species" mean "widely spread species"?
2) Failed to understand "fourteen in number at the fourteen-thousandth generation". fourteen in number? Supposed the species is pig, 14 pigs (in number) are understood clearly, but it is not consistent with the context.

Context:

But we may go further than this. The original species of our
genus were supposed to resemble each other in unequal
degrees, as is so generally the case in nature; species (A) being
more nearly related to B, C, and D than to the other species; and
species (I) more to G, H, K, L, than to the others. These two
species (A and I), were also supposed to be very common and
widely diffused species, so that they must originally have had
some advantage over most of the other species of the genus.
Their modified descendants, fourteen in number at the fourteen-
thousandth generation, will probably have inherited some of the
same advantages: they have also been modified and improved in
a diversified manner at each stage of descent, so as to have
become adapted to many related places in the natural economy
of their country. It seems, therefore, extremely probable that they
will have taken the places of, and thus exterminated, not only
their parents (A) and (I), but likewise some of the original species
which were most nearly related to their parents. Hence very few
of the original species will have transmitted offspring to the
fourteen-thousandth generation. We may suppose that only one
(F) of the two species (E and F) which were least closely related
to the other nine original species, has transmitted descendants to
this late stage of descent.