110 THE STRUCTURE OF EVOLUTIONARY THEORY
(3) Taxonomic disparity of endemic species within groups records ease of
access, not created fit to oceanic environments: "Thus in the Galapagos Islands
nearly every land bird, but only two out of the eleven marine birds, are peculiar;
and it is obvious that marine birds could arrive at these islands more easily than
land birds" (pp. 390-391).
(4) Biotas of oceanic islands often lack the characteristic groups of similar
habitats on continents. On these islands, endemic members of other groups often
assume the ecological roles almost always occupied by more appropriate or more
competitive taxa in the richer faunas of continents—for example, reptiles on the
Galapagos, or wingless birds on New Zealand, acting as surrogates for mammals.
(5) In endemic island species, features operating as adaptations in related
species on continents often lose utility when their island residences do not feature
the same environment: "For instance, in certain islands not tenanted by mammals,
some of the endemic plants have beautifully hooked seeds; yet few relations are
more striking than the adaptation of hooked seeds for transportal by the wool and
fur of quadrupeds. This case presents no difficulty on my view, for a hooked seed
might be transported to an island by some other means; and the plant then
becoming slightly modified, but still retaining its hooked seeds, would form an
endemic species, having as useless an appendage as any rudimentary organ" (p.
392).
(6) Peculiar morphological consequences often ensue when creatures seize
places usually inhabited by other forms that could not reach an island. Many
plants, herbaceous in habit on continents, become arboraceous on islands otherwise
devoid of trees.
(7) Suitable organisms frequently fail to gain access to islands. Why do so
many oceanic islands lack frogs, toads, and newts that seem so admirably adapted
for such an environment? "But why, on the theory of creation, they should not have
been created there, it would be very difficult to explain" (p. 393).
(8) Correlation of biota with distance. Darwin could find no report of
terrestrial mammals on islands more than 300 miles from a continent. He presents
the obvious evolutionary explanation for a disturbing creationist conundrum:
It cannot be said, on the ordinary view of creation, that there has not been
time for the creation of mammals; many volcanic islands are sufficiently
ancient, as shown by the stupendous degradation which they have suffered
and by their tertiary strata: there has also been time for the production of
endemic species belonging to other classes ... why, it may be asked, has the
supposed creative force produced bats and no other mammals on remote
islands? On my view this question can easily be answered; for no terrestrial
mammal can be transported across a wide space of sea, but bats can fly
across (p. 394).(9) Correlation with ease of access. Creatures often manage to cross shallow
water barriers between a continent and island, but fail to negotiate deep-water gaps
of the same distance.