10,000 of physiological variety to 90,000 of normal variety.
2d " 1,220 + 10,000 again produced.
3d " 16 + 1,220 + 10,000 do. = 11,236
4th " O + 16 + 1,220 + 10,000 do. = 11,236
5th " O + 16 + 1,220 + 10,000 = 11,236
and so on for any number of generations.
In the preceding discussion we have given the theory the advantage of
the large proportion of 10 per cent of this very exceptional variety
arising in its midst year by year, and we have seen that, even under
these favourable conditions, it is unable to increase its numbers much
above its starting-point, and that it remains wholly dependent on the
continued renewal of the variety for its existence beyond a few years.
It appears, then, that this form of inter-specific sterility cannot be
increased by natural or any other known form of selection, but that it
contains within itself its own principle of destruction. If it is
proposed to get over the difficulty by postulating a larger percentage
of the variety annually arising within the species, we shall not affect
the law of decrease until we approach equality in the numbers of the two
varieties.
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