Soon after Darwin’s return he moved to London for the two most active
years of his life, to care for his collections and to write up his
observations. At this moment came the third of the great turning-points
in his life, which as a mysteriously disguised blessing was brought
about through ill health. In London he was entering official duties and
public scientific service which would undoubtedly have increased and
interfered more and more seriously with his work. We can only count it
as one of the most fortunate circumstances in the history of science
that Darwin at the age of thirty-three was forced to leave London and to
move to Down. Here for forty years he never knew for one day the health
of an ordinary man; his life was one long struggle against the strain of
sickness. But unrealized by him there was the compensation of a mind
undisturbed by the constant interruption of outside affairs, such
interruption as killed Huxley and is killing so many fine and ambitious
men today. When I saw Huxley and Darwin side by side in 1879, the one
only fifty-four, the other seventy, the younger man looked by far the
more careworn of the two. Huxley, the strong man, broke down mentally at
fifty-six; Darwin, the invalid, was vigorous mentally at seventy-two.
Darwin’s writings fall into three grand series. In the nine years after
he returned from the voyage, or between his twenty-seventh and
thirty-sixth years, Darwin wrote the first series, including his
pre-evolutionary geological and zoological works, his “Coral Reefs”
(1842), his “Zoology and Geology of the Voyage of the _Beagle_”
(1844–1846), his “Journal of Researches,” the popular narrative of his
voyage (1845). Darwin’s ill health thereafter shut him off from geology,
although his last volume, “The Earthworm,” was in a sense geological.
It is characteristic of the life of every great man that his genius and
his own self-analysis instinctively guide him to discover his mental
needs.
Until the age of forty-five Darwin in his own opinion had not completed
his education, in the sense that education is a broad and exact
training. He now proceeded to fill the one gap in his training by
devoting the eight years of his life between thirty-seven and forty-five
to a most laborious research upon the barnacles, or Cirripedia. This
gave him the key to the principles of the natural or adaptively
branching and divergent arrangement of animals through the laws of
descent as set forth in the “Origin,” which he certainly could not have
secured in any other way. The value he placed on his work on the
barnacles is of especial import today when systematic work is so lightly
esteemed by many biologists, young and old. Darwin subsequently, in the
words of Hooker, “recognized three stages in his career as a biologist,
the mere collector at Cambridge, the collector and observer on the
_Beagle_ and for some years afterwards, and the trained naturalist
after, and only after, the Cirripede work.”
Long before this, however, at the age of twenty-eight, Darwin had begun
his career as a Darwinian. In July, 1837, he began his notes on the
transmutation of species, based on purely Baconian principles, on the
rigid collection of facts which would bear in any way on the variations
of animals and plants under domestication and in nature. Rare as was his
reasoning power, his powers of observation were of a still more distinct
order. He persistently and doggedly followed every clew; he noticed
little things which escaped others; he always noted exceptions and at
once jotted down facts opposed to his theories. On the voyage the
marvellous adaptations of animals and plants had been his greatest
puzzle. Fifteen months later, in October, 1838, in reading the work of
Malthus, on “Population,” there flashed across his mind the threefold
clew of the struggle for existence, of constant variability, and of the
selection of variations which happen to be adaptive.
The three memorable features of Darwin’s greatest work, “The Origin of
Species,” are, that he was twenty-one years in preparing it, that,
although by 1844 he was a strongly convinced evolutionist and natural
selectionist, he kept on with his observations for fifteen years, and
the volume even then would have been still longer postponed but for a
wonderful coincidence, which constitutes the third and not the least
memorable feature. This coincidence was that Wallace had also become an
evolutionist and had also discovered the principle of natural selection
through the reading of the same essay of Malthus. It is further
remarkable that of all persons Wallace selected Darwin as the one to
whom to send his paper. It was then through the persuasion of the great
botanist Hooker, who had known Darwin’s views for thirteen years, that
these independent discoveries were published jointly on July 1, 1858.
All the finest points of Darwin’s personal character were displayed at
this time; in fact, the entire Darwin-Wallace history up to and
including Wallace’s noble and self-depreciatory tribute to Darwin on
July 1 of last summer, is one of the brightest chapters in the history
of science. Wallace himself pointed out the very important distinction
that while the theories contained in the two papers published fifty
years ago were nearly identical, Wallace had deliberated only three days
after coming across the passage in Malthus, while Darwin had deliberated
for fifteen years. He modestly declared that the respective credit
should be in the ratio of fifteen years to three days.
Several months past the age of fifty Darwin published his epoch-making
work (November, 1859), and despite ill health, between fifty and
seventy-three he produced the nine great volumes which expand and
illustrate the views expressed in “The Origin of Species.”
A parallel to this remarkable late productiveness is that of Kant, who
also put forth his greatest work after fifty. Let those past the five
decades take heart, for it appears that while there are inborn
differences between men in this regard, imagination, observation,
reasoning and production do not necessarily dim with age. Darwin’s mind
remained young and plastic to the end; his latest and one of his most
characteristic works, “The Formation of Vegetable Mould through the
Action of Earth Worms,” was published at the age of seventy-two, after
forty-four years of observation. It contained another and perhaps the
most extreme demonstration of Lyell’s principle that vast changes in
nature are brought about by the slow operation of infinitesimal causes.
Three of Darwin’s succeeding volumes are a filling out of the “Origin.”
“The Variation of Animals and Plants under Domestication” (two volumes,
1868) presents the entire fabric of the notes begun twenty-one years
before on the transmutation of species. “The Descent of Man” (1871) was
another logical outcome of the “Origin,” yet it was only faintly
adumbrated by a single allusion in that work to the fact that the
transmutation of species necessarily led to the evolution of man. The
“Descent” marks the third of the great dates in the history of thought,
as the “Origin” marks the second, because it is the final step in the
development of ideas which began with Copernicus in 1543. The world-wide
sensation, the mighty _storm_ produced by this bold climax of Darwin’s
work, is so fresh in the memory of all that a mere allusion suffices.
The evolutionary or genetic basis for modern psychology as stated in
“The Descent of Man” was given still more concrete form in Darwin’s
succeeding and most delightful volume, “The Expression of the Emotions”
(1872).
The knowledge of zoology and anatomy displayed in these four
evolutionary volumes came from direct observation, vast and systematic
reading and note-taking from the simple materials which Darwin could
collect at Down. Always penetrating as these observations are, they are
still, in my opinion, surpassed in beauty and ingenuity by his
marvellous work on plants, published between 1862 and 1880. Here the
principles of co-adaptation of plants and insects in cross- and
self-fertilization, in climbing plants and insectivorous plants, in
forms of flowers, in movements of plants, are all brought forth in
support of the theory of natural selection and the operation of unknown
laws. Darwin’s most precise observations and some of his most brilliant
discoveries recorded in these volumes laid the foundations of modern
experimental botany.
Of his method Darwin writes:
From my early youth I had the strongest desire to understand or
explain whatever I observed, that is, to group facts under some
general laws. My mind seems to have become a kind of machine for
grinding general laws out of large collections of facts.
The only work which Darwin wrote deductively was his “Coral Reefs.”
Every other volume came through the inductive-deductive process, that
is, through an early assemblage of facts followed by a series of trial
hypotheses, each of which was rigidly tested by additional facts. The
most central of these trial hypotheses was that of the building up of
adaptations through the selection of the single adaptive variation out
of the many fortuitous variations, and this Darwin was unable to rigidly
test by facts but was obliged to leave for verification or disproof by
work after him.