fever and sweating to be repeated over many days. In this semi-delirious state ideas
would flash before him and then disappear. The question of the origin of species was
always on his mind and fortunately there had been a copy of Principles of Population
by Thomas Malthus in the Leicester town library. As in the case of Charles Darwin, it
was Malthus’ ideas that provided the breakthrough:
I was suffering from a rather severe attack of intermittent fever, which prostrated me for
several hours every day during the cold and succeeding hot fits. During one of these fits,
while again considering the problem of the origin of species, something led me to think of
Malthus’ essay on population (which I had read about 10 years before), and the ‘positive
checks’—war, disease, famine, accidents, etc.—which he adduced as keeping all savage
populations nearly stationary. It then occurred to me that these checks must also act upon
animals, and keep down their numbers; and as they increase so much faster than man does,
...it was clear that these checks in their case must be far more powerful ... There suddenly
flashed upon me the idea of the survival of the fittest—that the individuals removed by these
checks must be, on the whole, inferior to those that survived.Wallace had noted that certain beetles always adapted their coloration according
to their environment, so they were less conspicuous to predators. According to his
theory a beetle, for example, might be produced in many different types of coloration
but ‘the fittest’ – in this case the least conspicuous – would be most likely survive
to reproduce. By this method the superior ‘variety’ would then expand and could
eventually replace its soon to be extinct ancestor:
Most or perhaps all the variations from the typical form of a species must have some definite
effect, however slight, on the habits or capacities of the individuals. Even a change of colour
might by rendering them more or less distinguishable, affect their safety.As soon as he had recovered from his malarial fevers, Wallace began making notes
of these thoughts and on his return to Ternate he began writing his famous paper
entitled ‘On the Tendency of Varieties to Depart Indefinitely from the Original Type’
which he dated Ternate, February 1858. He remembered the letter he had received
from Charles Darwin related to his studies on how species and varieties differ from
each other. Surely this was the breakthrough Darwin was looking for:
The same evening I did this pretty fully, and on two succeeding evenings wrote it out
carefully in order to send it to Darwin by the next post, which would leave in a day or two
... I said I hoped the idea would be as new to him as it was to me, and that it would supply164 Where Australia Collides with Asia
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