Alfred Russel Wallace OM, FRS (8 January 1823 –
7 November 1913) was a British naturalist, explorer, geographer, anthropologist and biologist.
He did extensive fieldwork first in the Amazon River basin, and then in the
Malay Archipelago, where he identified the Wallace
line dividing the fauna of Australia from that of Asia.
He is best known for independently proposing a theory of natural selection which
prompted Charles Darwin to publish his own more developed and researched theory sooner
than intended. Wallace was also one of the leading evolutionary thinkers of the 19th century who made a number of other
contributions to the development of evolutionary theory, including the concept of warning
colouration in animals, and the Wallace effect. He was also considered the 19th
century’s leading expert on the geographical distribution of animal species and is sometimes called the "father of
biogeography".[1]
Wallace was strongly attracted to radical ideas. His advocacy of spiritualism and his
belief in a non-material origin for the higher mental faculties of humans
strained his relationship with the scientific establishment, especially with other early proponents of evolution. He was critical
of what he considered to be an unjust social and economic system in 19th century Britain, and was one of the first prominent
scientists to raise concerns over the environmental impact of human activity.
Biography
Early life
A Photo from Wallace's autobiography shows the building Wallace and his brother John designed and built for the
Mechanics Institute of Neath.
Wallace was born in the village of Llanbadoc, near Usk,
Monmouthshire, Wales.[2] He was the eighth of nine children of Thomas Vere Wallace and Mary Anne Greenell.
His mother was from a respectable middle-class English family from Hertford. Thomas Wallace was
of Scottish ancestry and his family, like many Scottish Wallaces, claimed a connection
to William Wallace, the leader of a 13th-century rising against England. Thomas Wallace
received a law degree but never actually practiced law. He inherited some income-generating property, but bad investments and
failed business ventures resulted in a steady deterioration of the family's financial position.[3]
When Wallace was five years old, his family moved to Hertford, north of London,
where he attended Hertford Grammar School until financial difficulties forced his
family to withdraw him in 1836.[4] Wallace then moved to
London to live and work with his older brother John, a 19-year-old apprentice
builder. This was a stopgap measure until William, his oldest brother, was ready to take him on as an apprentice surveyor. While there he attended lectures and read books at the London Mechanics Institute, where he was exposed to the radical political ideas of social reformers like
Robert Owen and Thomas Paine. He left London in 1837
to live with William and work as his apprentice for six years. At the end of 1839 they moved to Kington near the Welsh border before eventually settling at Neath
in Glamorgan, and between 1840 and 1843, Wallace did surveying work in the countryside of the
west of England and Wales.[5][6] By the
end of 1843 William's business had declined due to difficult economic conditions, and Wallace left in January.
After a brief period of unemployment, he was hired as a master at the Collegiate School in Leicester to teach drawing, map making, and surveying. Wallace spent a lot of time at the Leicester library
where he read An Essay on the Principle of Population by
Thomas Malthus and where one evening he met the entomologist Henry Bates. Bates was only 19 years old but had already published a paper on beetles in the journal
Zoologist. He befriended Wallace and started him collecting insects.[7][8] William died in March 1845,
and Wallace left his teaching position to assume control of his brother's firm in Neath. He and his brother John were unable to
make the business work, and after a couple of months Wallace found work as a civil engineer for a nearby firm that was working on
a survey for a proposed railway in the Vale of Neath. Wallace's work on the survey involved
spending a lot of time outdoors in the countryside, allowing him to indulge his new passion for collecting insects. Wallace was
able to persuade his brother John to join him in starting another architecture and civil engineering firm, which carried out a
number of projects including designing a building for the Mechanics Institute of Neath. William Jevons, the founder of that
institute, was impressed by Wallace and persuaded him to give lectures there on science and engineering. In the autumn of 1846 he
and John were able to purchase a cottage near Neath, where they lived with their mother and sister Fanny (his father had died in
1843).[9][10] During this period he read avidly, exchanging letters with Bates about the anonymous evolutionary
treatise Vestiges of the Natural History of Creation,
Charles Darwin's Journal and Remarks, and Charles Lyell's
Principles of Geology.[11]
Exploration and study of the natural world
A map from
The Malay Archipelago shows Wallace's travels around that area.
Inspired by the chronicles of earlier traveling naturalists including Alexander von
Humboldt, Charles Darwin, and William
Henry Edwards, Wallace decided that he too wanted to travel abroad as a naturalist.[12] In 1848 Wallace and Henry Bates
left for Brazil aboard the Mischief. Their intention was to collect insects and other
animal specimens in the Amazon Rainforest and sell them to collectors back in England.
They also hoped to gather evidence of the transmutation of species. Wallace and
Bates spent most of their first year collecting near Belém do Pará, then explored inland
separately, occasionally meeting to discuss their findings. In 1849, they were briefly joined by another young explorer, botanist
Richard Spruce, along with Wallace's younger brother Herbert; Herbert left soon after
(dying two years later from yellow fever), but Spruce, like Bates, would spend over ten
years collecting in South America.[13]
Wallace continued charting the Rio Negro for four years, collecting specimens and making
notes on the peoples and languages he encountered as well as the geography, flora, and fauna.[14] On 12 July 1852,
Wallace embarked for England on the brig Helen. After twenty-eight days at sea, balsam in
the ship's cargo caught fire and the crew was forced to abandon ship. Wallace's entire collection was lost, and he could only
save part of his diary and a few sketches. Wallace and the crew spent ten days in an open boat before being picked up by the brig
Jordeson.[15]
After his return to England, Wallace spent eighteen months in London living on the insurance payment for his lost collection
and selling the surviving remnants. During this period, despite having lost almost all of the notes from his South American
expedition, he wrote six academic papers (which included "On the Monkeys of the Amazon") and two books; Palm Trees of the
Amazon and Their Uses and Travels on the Amazon.[16] He also made connections with a number of other British naturalists—most significantly,
Darwin.[17][18]
An illustration from
The Malay Archipelago depicts the flying frog Wallace discovered.
From 1854 to 1862, Wallace travelled through the Malay Archipelago or
East Indies (now Malaysia and Indonesia), to collect specimens for sale and to study nature. His observations of the marked zoological
differences across a narrow strait in the archipelago led to his proposing the zoogeographical boundary now known as the
Wallace line. Wallace collected more than 125,000 specimens in the Malay Archipelago (more
than 80,000 beetles alone), and more than a thousand of them represented species new to science.[19] One of his better known species descriptions during this trip is the gliding
tree frog Rhacophorus nigropalmatus, known as Wallace's
flying frog. While he was exploring the archipelago he refined his thoughts about evolution
and had his famous insight on natural selection.
His studies and adventures there were eventually published in 1869 as The Malay
Archipelago. The Malay Archipelago became one of the most popular journals of scientific exploration of the
19th century, kept continuously in print by its original publisher (Macmillan) into the 2nd decade of the 20th century. It was
praised by scientists such as Darwin (to whom the book was dedicated), and Charles Lyell,
and by non scientists such as the novelist Joseph Conrad who called it his "favorite
bedside companion", and used it as source of information for several of his novels, especially Lord
Jim.[20]
A photograph of A.R. Wallace taken in
Singapore in 1862.
Return to England, marriage and children
In 1862 Wallace returned to England, where he moved in with his sister Fanny Sims and her husband Thomas. While he was
recovering from the rigours of his travels Wallace organized his collections, and gave numerous lectures about his adventures and
discoveries to scientific societies such as the Zoological Society of
London. Later that year he visited Darwin at home, and became friendly with both Charles
Lyell and Herbert Spencer.[21] During the 1860s Wallace wrote papers and gave lectures defending natural selection, and
corresponded with Darwin about a variety of topics including sexual selection,
warning colouration, and the possible effect of natural selection on hybridization and the
divergence of species.[22] In 1865 he began investigating
spiritualism.[23]
After a year of courtship, Wallace became engaged in 1864 to a young woman whom in his autobiography he would only identify as
Miss L. However, to Wallace's great dismay, she broke off the engagement.[24] In 1866 Wallace married Annie Mitten. Wallace had been introduced to Mitten through
Richard Spruce, who had befriended Wallace in Brazil, and who was also a good friend of
Annie Mitten's father, William Mitten, an expert in mosses. In 1872, Wallace had a house built of concrete on land he leased in
Grays in Essex where he lived until 1876. The Wallaces had three children; Herbert (1867–1874) who
died in childhood, Violet (1869–1945), and William (1871–1951).[25]
Financial struggles
In the late 1860s and 1870s Wallace was very concerned about the financial security of his family. While he was in the Malay
Archipelago the sale of specimens had brought in a considerable amount of money, which had been carefully invested by the agent
who sold the specimens for Wallace. However, on his return to England Wallace made a series of bad investments in railways and
mines that squandered most of the money, and he found himself badly in need of the proceeds from the publication of
The Malay Archipelago.[26] Despite assistance from his friends he was never able to secure a permanent salaried position such
as curatorship of a museum. In order to remain financially solvent Wallace worked grading government examinations, wrote 25
papers for publication between 1872 and 1876 for various modest sums, and was paid by Lyell and Darwin to help edit some of their
own works.[27] In 1876 Wallace needed a £500 advance from the publisher of The Geographical Distribution of Animals to avoid having to
sell some of his personal property.[28] Darwin was very
aware of Wallace's financial difficulties and lobbied long and hard to get Wallace awarded a government pension for his lifetime
contributions to science. When the £200 annual pension was awarded in 1881 it helped to
stabilize Wallace's financial position by supplementing the income from his writings.[29]
Social activism
John Stuart Mill was impressed by remarks criticizing English society that Wallace
had included in The Malay Archipelago, and asked him to join the general committee of his Land Tenure Reform Association,
but the association dissolved after Mill's death in 1873 and Wallace wrote only a handful of articles on political and social
issues prior to 1879. However, in that year he entered the debates over trade policy and land
reform in earnest. He believed that rural land should be owned by the state and leased to people who would make whatever
use of it that would benefit the largest number of people, thus breaking the often-abused power of wealthy landowners in English
society. In 1881 Wallace was elected as the first president of the newly formed Land Nationalisation Society. The next year he
published a book, Land Nationalisation; Its Necessity and Its Aims, on the subject. He criticized England's
free trade policies for the negative impact they had on working class people.[30][18] In 1889 Wallace read Looking Backward by
Edward Bellamy and declared himself a socialist.[31] These ideas led him to
oppose both Social Darwinism and Eugenics, ideas
supported by other prominent 19th century evolutionary thinkers, on the grounds that contemporary society was too corrupt and
unjust to allow any reasonable determination of who was fit or unfit.[32] In 1898 Wallace wrote a paper advocating a pure paper money system, unbacked by silver or gold,
which impressed the economist Irving Fisher so much that he dedicated his 1920 book
Stabilizing the Dollar to Wallace.[33] Wallace
wrote extensively on other social topics including his support for woman's suffrage,
and the dangers and wastefulness of militarism.[34][35]
Wallace continued his social activism for the rest of his life, publishing the book The Revolt of Democracy just weeks
before his death.[36]
Wallace continued his scientific work in parallel with his social commentary. In 1880 he published Island Life as a
sequel to The Geographic Distribution of Animals. In November 1886 Wallace began a ten month trip to the United States to give a series of popular lectures. Most of the lectures were on Darwinism (evolution and
natural selection), but he also gave speeches on biogeography, spiritualism, and
social/economic reform. During the trip he was reunited with his brother John who had emigrated to California years before. He also spent a week in Colorado, with the American botanist
Alice Eastwood as his guide, exploring the flora of the Rocky Mountains and gathering evidence that would lead him to a theory on how glaciation might explain
certain commonalities between the mountain flora of Europe, Asia and North America, which he published in 1891 in the paper
"English and American Flowers". He met many other prominent American naturalists and viewed their collections. His 1889 book
Darwinism used information he collected on his American trip, and information he had compiled for the lectures.[37][38]
Death
On 7 November 1913, Wallace died at home in the country
house he called Old Orchard, which he had built a decade earlier.[39] He was 90 years old. His death was widely reported in the press. The New York Times called him "the last of the giants belonging to that wonderful group of
intellectuals that included, among others, Darwin, Huxley, Spencer, Lyell, and Owen, whose daring investigations revolutionized
and evolutionized the thought of the century." Another commentator in the same edition said “No apology need be made for the few
literary or scientific follies of the author of that great book on the 'Malay Archipelago'.”[40] Some of Wallace's friends suggested that he be buried in Westminster Abbey, but his wife followed his wishes and had him buried in the small cemetery at
Broadstone, Dorset.[39] Several prominent British scientists formed a committee to have a medallion of Wallace
placed in Westminster near where Darwin had been buried. The medallion was unveiled on November
1, 1915.
Theory of evolution
Early evolutionary thinking
Unlike Darwin, Wallace began his career as a travelling naturalist already believing in the transmutation of species. The concept had been advocated by Jean-Baptiste Lamarck, Geoffroy
Saint-Hilaire, Erasmus Darwin, and Robert
Grant, among others. It was widely discussed, but not generally accepted by leading naturalists, and was considered to
have radical, even revolutionary connotations.[41][42] Prominent anatomists and geologists such as Georges Cuvier,
Richard Owen, Adam Sedgwick, and Charles Lyell attacked it vigourously.[43][44] It has been suggested
that Wallace accepted the idea of the transmutation of species in part because he was always inclined to favour radical ideas in
politics, religion and science[41], and
because he was unusually open to marginal, even fringe ideas in science.[45]
He was also profoundly influenced by Robert Chambers' work Vestiges of the Natural History of Creation, a highly controversial work
of popular science published anonymously in 1844 that advocated an evolutionary origin for the solar system, the earth, and
living things.[46] Wallace wrote to Henry Bates in 1845:
I have a rather more favourable opinion of the ‘Vestiges’ than you appear to have. I do not consider it a hasty
generalization, but rather as an ingenious hypothesis strongly supported by some striking facts and analogies, but which remains
to be proven by more facts and the additional light which more research may throw upon the problem. It furnishes a subject for
every student of nature to attend to; every fact he observes will make either for or against it, and it thus serves both as an
incitement to the collection of facts, and an object to which they can be applied when collected.[47]
Wallace deliberately planned some of his field work to test the hypothesis that under an evolutionary scenario closely related
species should inhabit neighbouring territories.[41] During his work in the Amazon basin he came to realize that geographical barriers—such as the
Amazon and its major tributaries—often separated the ranges of closely allied species, and he included these observations in his
1853 paper "On the Monkeys of the Amazon".[48] Near the
end of the paper he asks the question "Are very closely allied species ever separated by a wide interval of country?"
In February 1855, while working in the state of Sarawak on the island of Borneo, Wallace wrote "On the Law Which has Regulated the Introduction of Species", a paper which was published
in the Annals and Magazine of Natural History in September 1855. In
this paper he gathered and enumerated general observations regarding the geographic and geologic distribution of species
(biogeography). His conclusion that "Every species has come into existence coincident both
in space and time with a closely allied species" has come to be known as the "Sarawak Law". Wallace thus answered the question he
had posed in his earlier paper on the monkeys of the Amazon river basin. Although it contained no mention of any possible
mechanisms for evolution, this paper foreshadowed the momentous paper he would write three years later.[49]
The paper shook Charles Lyell's belief that species were immutable. Although his friend Charles Darwin had written to him in 1842 expressing support for transmutation, Lyell had continued to be
strongly opposed to the idea. Around the start of 1856 he told Darwin about Wallace's paper, as did Edward Blyth who thought it "Good! Upon the whole!… Wallace has, I think put the matter well; and according
to his theory the various domestic races of animals have been fairly developed into species." Despite this hint, Darwin
mistook Wallace's conclusion for the progressive creationism of the time and
wrote that it was "nothing very new… Uses my simile of tree [but] it seems all creation with him." Lyell was more impressed, and
opened a notebook on species where he grappled with the consequences, particularly for human ancestry. For the first time Darwin
now spelt out the full details of natural selection to Lyell, and although Lyell could
not agree, he urged Darwin to publish to establish priority. Darwin demurred at first, then began writing up a species
sketch of his continuing work in May 1856.[50]
Natural selection and Darwin
- See also: Publication of Darwin's
theory
By February 1858 Wallace had been convinced by his biogeographical research in the Malay
Archipelago of the reality of evolution. As he later wrote in his autobiography:
The problem then was not only how and why do species change, but how and why do they change into new and well defined species,
distinguished from each other in so many ways; why and how they become so exactly adapted to distinct modes of life; and why do
all the intermediate grades die out (as geology shows they have died out) and leave only clearly defined and well marked species,
genera, and higher groups of animals?[51]
According to his autobiography, it was while he was in bed with a fever that Wallace thought about Thomas Malthus's idea of positive checks on human population growth, and came up with the idea of
natural selection.[52] Wallace said in his autobiography that he was on the island of Ternate at the time, but historians have questioned this, saying that on the basis of the collection registries
he wrote at the time, he was more likely to have been on the island of Gilolo.[53] Wallace describes it as follows:
It then occurred to me that these causes or their equivalents are continually acting in the case of animals also; and as
animals usually breed much more quickly than does mankind, the destruction every year from these causes must be enormous in order
to keep down the numbers of each species, since evidently they do not increase regularly from year to year, as otherwise the
world would long ago have been crowded with those that breed most quickly. Vaguely thinking over the enormous and constant
destruction which this implied, it occurred to me to ask the question, why do some die and some live? And the answer was clearly,
on the whole the best fitted live… and considering the amount of individual variation that my experience as a collector had shown
me to exist, then it followed that all the changes necessary for the adaptation of the species to the changing conditions would
be brought about… In this way every part of an animals organization could be modified exactly as required, and in the very
process of this modification the unmodified would die out, and thus the definite characters and the clear isolation of each new
species would be explained.[54]
The Darwin-Wallace medal was issued by the Linnean society on the 50th anniversary of the reading of Darwin and Wallace's papers
on
natural selection.
Wallace had once briefly met Darwin, and was one of the correspondents whose
observations Darwin used to support his own theories. Although Wallace's first letters to Darwin have been lost, he carefully
kept the letters he received.[55] In the first letter
dated 1 May 1857, Darwin commented that Wallace's letter of October
10th which he'd recently received as well as Wallace's paper "On the Law that has regulated the Introduction of New Species" of
1855 showed that they were both thinking alike and to some extent reaching similar conclusions, and said that he was preparing
his own work for publication in about two years time.[56]
The second letter of 22 December 1857, said how glad he was
that Wallace was theorising about distribution, adding that "without speculation there is no good and original observation" while
commenting that "I believe I go much further than you".[57] Wallace trusted Darwin's opinion on the matter, and sent him his February 1858 essay,
"On
the Tendency of Varieties to Depart Indefinitely From the Original Type", with the request that Darwin would review it and
pass it on to Charles Lyell if he thought it worthwhile.[58] On 18 June 1858, Darwin received the manuscript from Wallace. While Wallace's essay did not employ Darwin's term "natural
selection", it did outline the mechanics of an evolutionary divergence of species from similar ones due to environmental
pressures. In this sense, it was very similar to the theory that Darwin had worked on for twenty years, but had yet to publish.
Darwin sent the manuscript to Charles Lyell with a letter saying "he could not have made a
better short abstract! Even his terms now stand as heads of my chapters… he does not say he wishes me to publish, but I shall, of
course, at once write and offer to send to any journal."[59] Distraught about the illness of his baby son, Darwin put the problem to Charles Lyell and
Joseph Hooker who decided to publish the essay in a joint presentation together
with unpublished writings which highlighted Darwin's priority. Wallace's essay was presented to the Linnean Society of London on 1 July 1858, along with excerpts from an essay which Darwin had disclosed privately to Hooker in 1847 and a letter Darwin
had written to Asa Gray in 1857.[60]
Wallace accepted the arrangement after the fact, grateful that he had been included at all. Darwin's social and scientific
status was at that time far greater than Wallace's, and it was unlikely that Wallace's views on evolution would have been taken
as seriously. Lyell and Hooker's arrangement relegated Wallace to the position of co-discoverer, and he was not the social equal
of Darwin or the other elite British natural scientists. However, the joint reading of their papers on natural selection linked
Wallace's name to that of the more eminent Darwin. This, combined with Darwin's (as well as Hooker's and Lyell's) advocacy on his
behalf, gave Wallace much greater access to the highest levels of British science than he had previously enjoyed.[61] The reaction to the reading was muted, with the president of
the Linnean remarking in May 1859 that the year had not been marked by any striking discoveries,[62] but with Darwin's publication of The
Origin of Species later in 1859 its significance became apparent. When Wallace returned to England, he met Darwin and
the two remained friendly afterwards.
After the publication of Darwin’s Origin of Species Wallace became one
of its staunchest defenders. In one incident in 1863 that particularly pleased Darwin, Wallace published the short paper "Remarks
on the Rev. S. Haughton's Paper on the Bee's Cell, And on the Origin of Species" in order to utterly demolish a paper by a
professor of geology at the University of Dublin that had sharply criticized Darwin’s comments in the Origin on how
hexagonal honey bee cells could have evolved through natural selection.[63] Another notable defence of the Origin was "Creation by Law", a review Wallace wrote in 1867
for The Quarterly Journal of Science of the book The Reign of Law, which had been written by the Duke of Argyle as
a refutation of natural selection.[64] After an 1870
meeting of the British Association Wallace wrote to
Darwin complaining that there were "no opponents left who know anything of natural history, so that there are none of the good
discussions we used to have."[65]
Differences between Darwin's and Wallace's ideas on natural selection
Historians of science have noted that while Darwin considered the ideas in Wallace's paper to be essentially the same as his
own, there were differences.[66] Darwin emphasized
competition between individuals of the same species to survive and reproduce, whereas Wallace emphasized ecological pressure on
varieties and species forcing them to become adapted to their local environment or become extinct.[67][68] It
has been suggested that Wallace's emphasis on the importance of adaptation to the environment for survival and Darwin's emphasis
on competition between individuals of the same species was at the root of their disagreement over the importance of
sexual selection.[69]
Others have noted that another difference was that Wallace appeared to have envisioned natural selection as a kind of feedback
mechanism keeping species and varieties adapted to their environment.[70] They point to a largely overlooked passage of Wallace's famous
1858 paper:
The action of this principle is exactly like that of the centrifugal governor of
the steam engine, which checks and corrects any irregularities almost before they become evident; and in like manner no
unbalanced deficiency in the animal kingdom can ever reach any conspicuous magnitude, because it would make itself felt at the
very first step, by rendering existence difficult and extinction almost sure soon to follow.[58]
The cybernetician and anthropologist Gregory
Bateson would observe in the 1970s that though seeing it only as an illustration, Wallace had "probably said the most
powerful thing that’d been said in the 19th Century".[71] Bateson revisited the topic in his 1979 book Mind and Nature: A Necessary Unity, and other
scholars have continued to explore the connection between natural selection and systems
theory.[70]
Warning colouration and sexual selection
In 1867 Darwin wrote to Wallace about a problem he was having understanding how some
caterpillars could have evolved conspicuous colour schemes. Darwin had come to believe that sexual selection, an agency to which Wallace didn’t attribute the same importance as Darwin did,
explained many conspicuous animal colour schemes. However, Darwin realized that this could not apply to caterpillars. Wallace
responded that he and Bates had observed that many of the most spectacular
butterflies had a peculiar odour and taste, and that he had been told by John Jenner
Weir that birds would not eat a certain kind of common white moth because they found it unpalatable. "Now, as the white
moth is as conspicuous at dusk as a coloured caterpillar in the daylight", Wallace wrote back to Darwin that it seemed likely
that the conspicuous colour scheme served as a warning to predators and thus could have evolved through natural selection. Darwin
was impressed by the idea. At a subsequent meeting of the Entomological Society Wallace asked for any evidence anyone might have
on the topic. In 1869 Weir published data from experiments and observations involving brightly coloured caterpillars that
supported Wallace’s idea. Warning colouration was one of a number of contributions Wallace
made in the area of the evolution of animal colouration in general and the concept of
protective colouration in particular.[72] It was also
part of a life long disagreement Wallace had with Darwin over the importance of sexual selection. In his 1878 book Tropical
Nature and Other Essays he wrote extensively on the colouration of animals and plants and proposed alternative explanations
for a number of cases Darwin had attributed to sexual selection.[73] He revisited the topic at length in his 1889 book Darwinism.
Wallace effect
In 1889 Wallace wrote the book Darwinism which explained and defended natural selection. In it he proposed the
hypothesis that natural selection could drive the reproductive isolation of two varieties by encouraging the development of
barriers against hybridization. Thus contributing to the development of new species. He suggested the following scenario. When
two populations of a species had diverged beyond a certain point, each adapted to particular conditions, hybrid offspring would
be less well adapted than either parent form, and at that point natural selection will tend to eliminate the hybrids.
Furthermore, under such conditions natural selection would favour the development of barriers to hybridization, as individuals
that avoided hybrid matings would tend to have more fit offspring, and thus contribute to the reproductive isolation of the two
incipient species. This idea came to be known as the Wallace effect.[74] Wallace had suggested to Darwin that natural selection could play a role
in preventing hybridization in private correspondence as early as 1868, but had not worked it out to this level of
detail.[75] It continues to be a topic of research in
evolutionary biology today with both computer simulation and empirical results supporting its validity.[76]
An Illustration from the chapter on the application of
natural selection to man in
Wallace's 1889 book
Darwinism shows a chimpanzee.
Application of theory to man, and role of teleology in evolution
In 1864 Wallace published a paper, "The Origin of Human Races and the Antiquity of Man Deduced from the Theory of 'Natural
Selection'", applying the theory to mankind. Darwin had not yet publicly addressed the subject, although Thomas Huxley had in Evidence as to Man's
Place in Nature.
Shortly afterwards Wallace became a spiritualist. At about the same time he began to
maintain that natural selection cannot account for mathematical, artistic, or musical genius, as well as metaphysical musings,
and wit and humour. He eventually said that something in "the unseen universe of Spirit" had interceded at least three times in
history: The first was the creation of life from inorganic matter. The second was the introduction of consciousness in the higher
animals, and the third was the generation of the higher mental faculties in mankind. He also believed that the raison d'être of the universe was the development of the human spirit.[77] These views greatly disturbed Darwin, who argued that spiritual appeals were
not necessary and that sexual selection could easily explain apparently non-adaptive
mental phenomena. While some historians have concluded that Wallace's belief that natural selection was insufficient to explain
the development of consciousness and the human mind was directly caused by his adoption of spiritualism, other Wallace scholars
have disagreed, and some maintain that Wallace never believed natural selection applied to those areas.[78][79] Reaction to Wallace's ideas on this topic among leading naturalists at the time varied.
Charles Lyell endorsed Wallace's views on human evolution rather than Darwin's.[80][81] However, many, including Huxley, Hooker and Darwin himself, were critical of Wallace.[82] As one historian of science has pointed out, Wallace's views
in this area were at odds with two major tenets of the emerging Darwinian philosophy, which were that evolution was not
teleological and that it was not anthropocentric.[83]
Assessment of Wallace's role in history of evolutionary theory
In many accounts of the history of evolution, Wallace is mentioned only in passing as simply being the "stimulus" to
publication of Darwin's own theory.[84] In reality,
Wallace developed his own distinct evolutionary views which diverged from Darwin's, and was considered by many (especially
Darwin) to be a leading thinker on evolution in his day, whose ideas could not be ignored. One historian of science has pointed
out that through both private correspondence and published works Darwin and Wallace exchanged knowledge and stimulated each
other's ideas and theories over an extended period.[85]
Wallace is the most cited naturalist in Darwin's Descent of Man, often in strong disagreement.[86] Wallace remained an ardent defender of natural selection for
the rest of his life. By the 1880s, evolution was widely accepted in scientific circles, but Wallace and August Weismann were nearly alone among prominent biologists in believing that natural selection was the
major driving force behind it.[87][88] In 1889 Wallace published the book Darwinism as a response to the
scientific critics of natural selection.[89] Of all
Wallace's books it is the most cited by scholarly publications.[90]
Spiritualism
In a letter to his brother in law in 1861, Wallace wrote:
…I remain an utter disbeliever in almost all that you consider the most sacred truths. I will pass over as utterly
contemptible the oft-repeated accusation that sceptics shut out evidence because they will not be governed by the morality of
Christianity… I am thankful I can see much to admire in all religions. To the mass of mankind religion of some kind is a
necessity. But whether there be a God and whatever be His nature; whether we have an immortal soul or not, or whatever may be our
state after death, I can have no fear of having to suffer for the study of nature and the search for truth, or believe that those
will be better off in a future state who have lived in the belief of doctrines inculcated from childhood, and which are to them
rather a matter of blind faith than intelligent conviction.[91]
Wallace was an enthusiast of phrenology,[92] and early in his career he experimented with hypnosis; then known
as mesmerism. He used some of his students in Leicester as subjects with considerable success.[93] When he began his experiments with mesmerism the topic was very controversial
and early experimenters, such as John Elliotson, had been harshly criticized by the
medical and scientific establishment.[94] Wallace drew a connection between his experiences with mesmerism and his later
investigations into spiritualism. In 1893 he wrote:
I thus learnt my first great lesson in the inquiry into these obscure fields of knowledge, never to accept the disbelief of
great men or their accusations of imposture or of imbecility, as of any weight when opposed to the repeated observation of facts
by other men, admittedly sane and honest. The whole history of science shows us that whenever the educated and scientific men of
any age have denied the facts of other investigators on a priori grounds of absurdity or impossibility, the deniers have always
been wrong.[95]
Wallace began investigating spiritualism in the summer of 1865, possibly at the urging of his older sister Fanny Sims who had
been involved with it for some time.[96] After reviewing
the literature on the topic and attempting to test the phenomena he witnessed at séances, he came
to accept that the belief was connected to a natural reality. For the rest of his life he remained convinced that at least some
séance phenomena were genuine, no matter how many accusations of fraud sceptics made, or how much evidence of trickery was
produced. Historians and biographers have disagreed about which factors most influenced his adoption of spiritualism. It has been
suggested by one biographer that the emotional shock he had received a few months earlier when his first fiancée broke their
engagement contributed to his receptiveness to spiritualism.[97] Other scholars have preferred to emphasize instead Wallace's desire to find rational and scientific
explanations for all phenomena, both material and non material, of the natural world and of human society.[98][94]
Spiritualism appealed to many educated Victorians who no longer found traditional
religious doctrine such as that of the Church of England acceptable, but who were
unsatisfied with the completely materialistic and mechanical view of the world that was increasingly emerging from 19th century
science.[99] However, several scholars who have
researched Wallace's views in depth have emphasized that for him spiritualism was a matter of science and philosophy rather than
religious belief.[98][94] Other prominent
19th century intellectuals involved with spiritualism included the social reformer Robert
Owen, who was one of Wallace’s early idols,[100]
the physicists William Crookes and Lord Rayleigh, the mathematician Augustus De
Morgan, and the Scottish publisher Robert Chambers.[101][102]
Wallace's very public advocacy of spiritualism and his repeated defence of spiritualist mediums against allegations of fraud
in the 1870s damaged his scientific reputation. It strained his relationships with previously friendly scientists such as
Henry Bates, Thomas Huxley, and even
Darwin who felt he was overly credulous. Others, such as the physiologist William
Benjamin Carpenter and zoologist E. Ray Lankester became openly and publicly
hostile to Wallace over the issue. Wallace and other scientists who defended spiritualism, notably William Crookes, were subject to much criticism from the press, with The
Lancet as the leading English medical journal of the time being particularly harsh. The controversy affected the
public perception of Wallace’s work for the rest of his career.[103] When in 1879 Darwin first tried to rally support among naturalists to get a civil pension awarded
to Wallace, Joseph Hooker responded:
Wallace has lost caste considerably, not only by his adhesion to Spiritualism, but by the fact of his having deliberately and
against the whole voice of the committee of his section of the British Association, brought about a discussion of on Spiritualism
at one of its sectional meetings. That he is said to have done so in an underhanded manner, and I well remember the indignation
it gave rise to in the B.A. Council.[104]
Hooker eventually relented and agreed to support the pension request.[105]
Biogeography and ecology
A map of the world from
The Geographical Distribution of Animals shows Wallace's 6 Biogeographical regions.
In 1872, at the urging of many of his friends including Darwin, Philip Sclater, and
Alfred Newton, Wallace began research for a general review of the geographic distribution
of animals. He was unable to make much progress initially, in part because classification systems for many types of animals were
in flux at the time.[106] He resumed the work in earnest
in 1874 after the publication of a number of new works on classification.[107] Extending the bird system developed by Sclater—which divided the earth into 6 separate geographic
regions for describing species distribution—to cover mammals, reptiles and insects as well, Wallace created the basis for the
zoogeographic regions still in use today. He discussed all of the factors then known to
influence the current and past geographic distribution of animals within each geographical region. These included the effects of
the appearance and disappearance of land bridges (such as the one currently connecting North America and South America), and the
effects of periods of increased glaciation. He provided maps that displayed factors, such as elevation of mountains, depths of
oceans, and the character of regional vegetation, that affected the distribution of animals. He also summarized all the known
families and genera of the higher animals and listed their known geographic distributions. The text was organized so that it
would be easy for a traveler to use to learn what animals could be found in a particular location. The resulting two volume work,
The Geographical Distribution of Animals, was published in 1876 and would serve as the definitive text on
