1897) PLACE OF ISOLATION IN ORGANIC EVOLUTION 241 
able to preserving them ; for while cross fertilisation (amphimixis) 
may stimulate variation, it also prevents the variations from 
progressing by their mutual interference, and thus it tends to 
keep a species constant, but ready to vary when circumstances 
require it to do so! Self-fertilisation, on the other hand, may be 
unfavourable to the production of variations, but when one does 
appear it has a good chance of being established. 
The general belief that breeding in-and-in is injurious has led 
to the conclusion that a large and healthy progeny cannot arise 
from a few parents if they are kept quite apart from all others. 
But that cross-fertilisation is not necessary for the rapid increase 
and continued health of the descendants from a few common an- 
cestors is proved by the successful naturalisation of many animals 
in New Zealand from very limited stocks. The honey-bee was 
introduced by the Reverend Mr Cotton, chaplain to Bishop Selwyn, 
who procured a few hives from Sydney; and, in 1866, wild bees 
were common in the forests of the North Island. Seven Chinese 
pheasants were introduced in 1851, and six more in 1856—more 
than half being cocks; and pheasant shooting near Auckland com- 
menced in 1865. <A few black swans were introduced by Sir 
Walter Buller in 1864. A few cirl buntings were turned out 
near Dunedin about 1868. <A very few silver-gray rabbits were 
released at Kaikoura; and, I believe, only three Tasmanian opos- 
sums were turned out in the forests of Southland; yet all these 
species are now abundant and healthy. The herd of deer in the 
Wairarapa (Wellington) has sprung from one stag and two hinds 
turned out in 1863; and the herds in other parts of New Zealand 
have all started from very few progenitors, Also many of the self- 
introduced insects—as the English lady-bird (Coccinella undecim- 
punetata), the drone-fly (Hristalis tenax), the horse-bot (Gastrophilus 
-equt), and Lucilia caesar, could only have been introduced in small 
numbers, for each has spread from a single centre; but yet they 
have been very successful. It is true that several failures to 
naturalise animals could also be given, but these failures do not 
invalidate the evidence suppled by successful naturalisation, and it 
is evident that, when the surroundings are favourable, it is quite 
possible for a few individuals to give rise to a new and vigorous 
species which might in time become dominant. 
Isolation must therefore be a true cause of the preservation of 
variations, and also it must be an important one. The artificial 
selection of animals and plants by man might just as well be called 
artificial isolation. The breeder, or the horticulturist, certainly 
selects the variation he wishes to preserve, but he also isolates it ; 
and it is the isolation which causes the variation to be preserved — 
1 See Professor H. R. Orr’s ‘‘ Development and Heredity,” p. 234. 
