Epilogue
The Wallace Line still stands as the westernmost reach of Australian species, but
there are now additional lines. The Weber Line is the easternmost extent of Asian
species and these two lines surround the enigmatic island of Sulawesi. Lydekker’s
Line follows close to the Australian continental shelf and is the westernmost extent of
Australian mammals.
On the Origin of Species received a devastating review by a Scottish engineer
named Fleeming Jenkin. In his review Jenkin pointed out that Darwin’s theory
foundered because there was no possibility of a new variant spreading throughout a
population. The prevalent theory of inheritance was that of blending and that offspring
were a blend of their parents’ characteristics. Therefore any useful new variation
should begin to be blended out as soon as the animal or plant started breeding with the
‘normal’ population.
Darwin knew this was a weakness in his theory and his incomplete research had
been another reason for delaying publication of the Origin. He needed a mechanism
of inheritance that could account for the reproduction, generation after generation,
of a stable, inheritable variation on which natural selection could work. How was an
advantageous trait passed on and more importantly how did it persist? In an attempt to
solve this question he bred snapdragons, crossing those bearing red flowers with those
bearing white flowers, and he gathered information from plant and animal breeders.
What was the mechanism in which cross-breeding worked? To get an insider’s view
of this craft he experimented with breeding pigeons and joined different pigeon clubs,
both high and low, where he met with more of the human species than was his norm.
‘I am hand and glove with all sorts of Fanciers, Spitalfields weavers and all sorts of
odd specimens of the Human species, who fancy Pigeons.’
Darwin published a paper entitled ‘Variations of Animals and Plants Under
Domestication’ in which he proposed a theory of inheritance which he called
pangenesis, where cells and tissues in the body adapt to the environment and these
cells are shed into the bloodstream as ‘gemmules’, which eventually lodge in the sex
organs and are then passed on to the next generation. He had no experimental evidence
for this but he needed a unit of inheritance transmitted through sexual reproduction.
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