The exciting biography of the co-discoverer of the theory of evolution by natural selection together with Charles Darwin is, in general, little known, since he is usually associated only with this scientific milestone. However, other equally important scientific contributions are usually forgotten, as well as his adherence to mesmerism and Spiritualism, issues that would end up determining his scientific theories in a decisive way.
He could perfectly be considered a Renaissance man. There were few fields of knowledge that resisted his unsatisfied curiosity. His interests were not limited only to natural sciences, although it was in this field where he excelled the most, mainly due to his independent discovery of the evolution of species by natural selection, a discovery that he would end up sharing with Charles Darwin. Broadly speaking, this theory predicts that species are transformed into others through the survival of those individuals with the appropriate characteristics that ensure their adaptation to the changing conditions of the environment and the elimination of the less fitted. A beautiful and elegant theory for its simplicity to explain the intricate and universal phenomenon of the evolution of species. A theory that Alfred Russel Wallace (1823-1913) conceived almost as a revelation.
It happened in 1858. The naturalist was completely unaware that Charles Darwin had been gathering empirical and experimental evidence for 20 years to present the same idea to the public. Wallace was at that time on the island of Ternate in Indonesia. By then he had already been traveling in the Malay archipelago for some time doing the typical things of a naturalist: collecting animal and plant specimens and observing nature. Also by then, Wallace was already fully convinced of the evolution of species, a controversial doctrine in his time. His pro-evolutionary defence is evident in his 1855 essay On the Law which has regulated the Introduction of New Species, where he firmly states:
“Every species has come into existence coincident both in space and time with a pre–existing closely allied species.”
The great enigma to be solved now was the mechanism behind this phenomenon. After contracting malaria, he was incapacitated for some time by intense fevers, but instead of resting, he continued to think about the great enigma. A few years earlier, Wallace had had the opportunity to travel through the Amazon rainforest. The enormous biodiversity of plants and animals that he was able to study during his travels stimulated him to wonder about the mystery of the geographical distribution of animals and plants and about the anatomical and behavioral singularities and similarities between species of different regions. These questions made him realize that all existing species of living beings were perfectly adapted to the present conditions of their respective environments. Finally, he would recall what Thomas Malthus commented in his An Essay on the Principle of Population when populations grew faster than resources: a struggle for existence is generated in which the sick, the weak and, in short, the less fitted tended to disappear. In a masterful way, Wallace put all the pieces together, giving birth on his own to one of the most relevant theories of science. As a result of this, he would write what is known as the Ternate’s essay, entitled On the Tendency of Varieties to Depart Indefinitely From the Original Type (1858). His aim was that Darwin (a renowned naturalist by then and with whom Wallace had been corresponding for some time) would review the manuscript and forward it to Charles Lyell (father of modern geology and a mutual friend of both) in case it was worthwhile. Darwin received the essay on June 18, 1858. In a letter to Charles Lyell along with the revised manuscript, he expressed his astonishment:
“[…] he could not have made a better short abstract! Even his terms now stand as heads of my chapters. Please return me the M.S. which he does not say he wishes me to publish; but I shall of course at once write & offer to send to any journal”
Wallace’s arguments, together with several Darwin’s comments, would end up being published before the Linnean Society on July 1, 1858, certifying Wallace as co-discoverer. And not only this. Stimulated by the work of his colleague and by the fear that someone might get ahead of him, Charles Darwin hurried to conclude his life’s work as soon as possible. Thus, on November 24, 1859, he published the work that would change everything: The Origin of Species.
This is the contribution for which Wallace is best known. However, he also theorized on agrarian reform and land nationalization, socialism, the controversial Mars canals, compulsory vaccination programs against smallpox, the origin and destiny of the human being, phrenology, mesmerism, or Spiritualism, of which he would end up being a faithful devotee. His affinity for these fields would lead him to clash with many of his scientific colleagues and to be the object of harsh criticism. Unfortunately, these aspects of his biography, already little known in the popular sphere, have often been forgotten. However, if they are not taken into account, we are condemned to a partial and biased interpretation of his intricate worldview.
His youthful experiencies greatly influenced his inclination towards radical or marginal ideas. Alfred Russel Wallace grew up in a relatively well-off family that ended up having financial problems. This forced him to enter the world of work at a very young age, having barely been able to go to school. Much of their culture and knowledge came from self-learning and his frequent visits to the “Halls of Science”, working-class educational institutions where revolutionary and anti-system doctrines were disseminated against orthodox science, religion and the government. This environment would predispose him to accept without too much difficulty groundbreaking and controversial ideas and concepts for the time, such as the evolution of the species, phrenology or Spiritualism.
“We have also neglected or rejected some important lines of investigation affecting our own intellectual and spiritual nature; and have in consequence made serious mistakes in our modes of education, in our treatment of mental and physical disease, and in our dealings with criminals.”
This is how Wallace introduces the chapter dedicated to the great nineteenth-century errors in his work Wonderful century (1898). Among these neglected lines of research, whose credibility should be placed at the same level as any fully accepted scientific theory, included phrenology, a pseudoscience founded in the late eighteenth century by Francis Joseph Gall, consisting in the connection of the behaviors, talents and intellectual faculties of people with the degree of development of certain regions of their cerebral cortex and the skull. Wallace’s first contact with phrenology occurred in his adolescence after reading George Combe’s The constitution of man (1828), a lawyer and leading exponent of phrenology in England. Later, around 1846-1847, his conviction would become unshakable because of the precise sketch that two phrenologists made of his personality traits by analyzing the shape of his head. He even acquired a phrenological bust to practice his skills in this field.
A few years earlier, he had begun to feel attracted to mesmerism, a doctrine named after its ideologist, the German physician Franz Anton Mesmer. According to his doctrine, all living beings are recipients of an energy similar to magnetism, baptized as animal magnetism. Mesmer claimed that the physician could transmit his magnetism to patients to induce a trance state and heal all their ills. Later, mesmerism would eventually give way to hypnosis. Wallace would frequently use this doctrine as a weapon against the narrow-mindedness of the scientific authorities because, in his view, they vilified without any reason a phenomenon whose authenticity was indisputable. For the naturalist, it was another of those neglected sciences that was worth vindicating. To this end, he devoted a good deal of effort through various experiments.
In 1844, when he was only 21 years old and a school teacher, he and his students attended a lecture on mesmerism. The speaker’s statement that everyone had, to a greater or lesser extent, the ability to hypnotize other people deeply touched Wallace. From then on, he carried out some experiments combining mesmerism and phrenology to reproduce the most common phenomena on his own. They consisted of inducing the expected phrenological reactions by touching the appropriate cranial organs while the volunteers were in a trance. He would also perform several purely hypnotic tests with the aim of inducing all kinds of behaviors in his volunteers. Several of these experiments were conducted in his own home with three boys from his school. As he recounts in his autobiography, he was able to generate catalepsy in different parts of the body, to induce them to keep a chair hanging from their arms for several minutes without suffering fatigue, to develop a state of drunkenness after drinking a glass of water, or to make them believe that their clothes were burning, to which they responded by taking them off in anguish. Similarly, they would lose their memory if Wallace so desired, being unable to remember their names until Wallace ordered them otherwise. An even greater success was the transmission of sensations. When Wallace tasted a food, the hypnotized boy was able to feel the same taste in his mouth, or if the scientist received punctures in any part of his body, the boy indicated that he also felt them by pointing to the same parts of his own body. With these verifications, Wallace was definitively convinced of the authenticity of mesmerism, awakening his interest in the extraordinary faculties of the human mind, which would lead him to explore other controversial and exciting subjects.
Of all the heterodox subjects in which Wallace was involved, Spiritualism was undoubtedly the one that most affected his way of conceiving reality, despite his initial skepticism. In July 1865 he experienced his baptism of fire. After returning to his native England from the tropics, he went to a friend’s house to conduct some spiritualistic sessions, encouraged by the rumors he had been hearing about communication with beings from beyond. In that first experience, Wallace was able to register for two hours knocks and vibrations on the table where they were all gathered. Their intensity progressively increased until the table began to vibrate strongly, as if it were a trembling animal. The séances were repeated a dozen times more, obtaining equally extraordinary results despite the controls imposed by Wallace to rule out possible fraud. Unable to find a convincing rational explanation, he would conclude that an unknown force was the cause of the mysterious manifestations.
In September of that same year he began to frequent Mrs. Marshall, a medium well known in London society. Wallace witnessed -sometimes in broad daylight- the levitation and involuntary movement of different objects or the divination of private and personal information of the attendees that the medium couldn’t know. During this period, he was also introduced to spiritualist literature, discovering that honorable people of great reputation and intelligence were convinced of the authenticity of mediumistic phenomena. Subsequently, Wallace would organize séances in his own home, where he could control to a greater extent the conditions of the tests. However, in order to ensure that results were obtained, he needed a person with the appropriate abilities to stimulate the phenomena. Thanks to his sister he would meet in 1866 the famous medium Agnes Guppy-Volckman, with whom he would become definitively convinced of the indisputable reality of the phenomena and spirits. The raps and the displacement of various objects constituted the most frequent prodigies. On one occasion, Wallace and several attendees observed how the table on which they were conducting the séance swayed for several seconds while it was suspended in the air several centimeters above the floor. Attempts to return it to the ground were in vain. To try to replicate these phenomena, another séance was conducted, although this time Wallace tied a thin strip of paper to the legs of the table, which was to be torn in case any of the attendees decided to cheat by lifting it with their feet. During the session, the table once again levitated and moved in the air. When the séance was over, Wallace was astonished to find that the strip of paper was still intact.
His experiences with Agnes Guppy would be enough to write a book, so we will highlight two more episodes to give an idea of the rich diversity of events that occurred in his presence. One of the séances took place at the home of a friend of Wallace. The medium and the other attendees settled around a table under a crystal chandelier with the lights off. Wallace’s friend held Agnes’ hands at all times. Meanwhile, another of the participants prepared several matches to light the room when the naturalist gave the order and to discover the trick in flagrante in case there was one. First they perceived that someone had removed the chair in which the medium was sitting, so that the woman had to stand. Next, Wallace heard
“a slight sound, such as might be produced by a person placing a wine-glass on the table, and at the same time a very slight rustling of clothes and tinkling of the glass pendants of the chandelier. Immediately my friend said, ” She is gone from me”.”
When the lights came on, the medium appeared sitting in her chair on the table. This deeply puzzled Wallace, unable to find an explanation as to how the corpulent woman could do all this without generating the slightest noise.
What Agnes was known for, however, was the materialization of plants and fruits. One of the first times this happened was at Wallace’s house. On this occasion, the reason for the meeting was to have a relaxed tea party. After four hours of conversation, flowers of various species appeared out of nowhere in a closed room, covered with dew and perfectly fresh and preserved, as if they had just been plucked. Of course, the naturalist did not see anyone bring these flowers into his house and all the attendees claimed to know nothing about them.
Wallace was deeply involved in Spiritualism and wherever he went he did not miss the opportunity to establish new contacts with experts or amateurs and to participate in new séances. For example, between 1886 and 1887, Wallace made a journey through the United States with the main objective of giving a series of seminars on his scientific investigations, although he would also dedicate part of his time to his other interests. He had the opportunity to meet prominent American spiritualists, such as Leland Stanford, governor of California and founder with his wife of the prestigious Stanford University. He also took the opportunity to hold several séances with his new friends. One of the most extraordinary events took place in the presence of several attendees at the home of Mrs. Ross. Before beginning the séance, Wallace thoroughly inspected the rooms of the house and sealed the doors of the room where the event was to take place. Once the medium had hidden herself in her cabinet behind some curtains, a procession of spirits began to appear before the attendees. First, from behind the curtains emerged Mrs. Ross with a female figure and a man. After they withdrew, three female figures of varying heights and dressed in white robes emerged. Another male figure followed, then a spirit with Indian features and another woman holding a baby, which Wallace was able to touch. At the end of the séance, Wallace hurried to examine the house again without being able to find any evidence of deception.
However, of all the potential evidence in favor of spirits, one of the most solid for Wallace was the photographs of spirits, as they would allow to objectively prove their existence. Without going any further, the scientist himself was the protagonist of this phenomenon. It happened during his first and only visit to Frederick Hudson, a photographer known to Mrs. Guppy, on March 14, 1874. Wallace had three photographs taken in different poses, and in all three an anthropomorphic mist appeared beside him. The first showed what appeared to be a male equipped with a short sword whom Wallace failed to identify. In the other two, on the other hand, the figure showed a striking resemblance to his mother, who was not only identified by Wallace, but also by his brothers and sister-in-law. It should be noted that the female figure appeared to be of a different age in the two photographs and that her position and characteristics did not coincide with any of the photographs that the Wallace family may have kept, thus resulting in a genuine and irrefutable proof for the scientist that further strengthened his conviction.
The multitude of collected experiences guaranteed Wallace’s firm adherence to Spiritualism. If this is not taken into account, it is difficult to assimilate his complex worldview. Wallace believed that Spiritualism was just as legitimate as any of the physical and natural sciences, since it was supported by innumerable evidences collected by many honorable people through their observations and experiments. However, the revelations coming from spirits, whose reality was useless to refute, transcended any materialistic attempt to elucidate the secrets of nature and the meaning of human existence. Spiritualistic phenomena and the descriptions of the afterlife were in harmony with the natural order of the universe, so they could be legitimately accepted without fear of contravening the natural laws, an argument often raised by critics. Thus, for example, just as in the evolution of organic life natural selection intervenes, in the spiritual sphere an analogous mechanism exerts its influence, which gave priority to the progress of those spirits who had dedicated their earthly life to the cultivation of the noblest faculties. In relation to spiritualistic phenomena, Wallace refused to consider them as supernatural, since they could be due to unknown mechanisms of interaction between the spirits and the material world actually. Presumably, beings of an ethereal nature could have, due to their advanced degree of development, such faculties and sensitivity that would allow them to interact with the ether of the universe, producing its vibration, in a similar way to other ordinary forces and energies. In this way all known paranormal phenomena would be generated. Far from being supernatural, they would respond, consequently, to natural dynamics generated by very advanced entities incomprehensible to our intellect.
Another fundamental aspect of spiritualism was the moral teachings transmitted during séances. These could be summarized in the following points in Wallace’s opinion: the human being is a dual being constituted by a spiritual, ethereal essence, the foundation of his moral and intellectual nature and destined to constant development, and another physical one with which it co-evolves; this duality is undone at the moment of death; the spirit remains unaltered during the transition to another body (demonstrated by communications with the deceased, who show themselves as they were in life); the destiny of individuals is constant moral and spiritual progress, which occurs through vital experiences during earthly existence. Consequently, our actions in life will have repercussions on our future existence.
Spiritualism would become Wallace’s main source of answers to solve the great mysteries of the universe. For example, the naturalist would speculate on the considerable role that ethereal beings would have played in the emergence of human nature and in the determination of our destiny, thus giving his personal answer to the existential questions “where do we come from?” and “where are we going?” So transcendental was the influence of this doctrine that he came to feel the need to convince his more reticent colleagues of the capital importance of this new science, since in the spirits the answers to the great questions were to be found. Perhaps that is why he tried to build a scientific foundation around Spiritualism and give it the same degree of credibility as the traditional sciences.
BEYOND NATURAL SELECTION
Whilst he was a strong advocate of Darwinism and considered natural selection as the omnipotent creative force of species, Wallace made an exception in the case of man, probably influenced by his spiritualistic beliefs. He argued that natural selection alone had not been able to develop the superior mental faculties of humans, considering necessary the complementary contribution of another force of a different nature. His conception rested on the utilitarian idea that nature never grants species superior endowments to those they really need for their daily survival.
As we have already mentioned, issues such as the human mind and consciousness attracted his attention, especially after his early contact with mesmerism. Likewise, his conversion to Spiritualism marks a milestorm in his metaphysics of human nature. In a first stage, prior to his conversion, he considered that, at the moment when consciousness and intellect appeared in primitive man, the mind acquired the exclusive role of assuring the adaptation of the human being to the changing conditions of the environment and of his psychological and social evolution. Thus, natural selection ceased its activity on the physical body, which ceased to mutate, to focus exclusively on the mind. This is why, for example, when faced with a prolonged drop in temperature over time, man did not develop more hair or fat to adapt to the new conditions. On the contrary, he make use of his prodigious intelligence to make a coat or build a shelter. Even Charles Darwin would express sympathy for this hypothesis.
After his contact with Spiritualism, he would introduce in his theories another more transcendental mechanism, dismissing the preponderant role of natural selection in the design of human nature and relegating it to an anecdotal second place. The extraordinary and exclusive faculties of human beings, such as morality, the capacity for abstraction, the understanding of complex concepts such as infinity, beauty, the sublime or mathematics, were meaningless in the light of natural laws, since they would have no effect on human survival. Likewise, if natural selection had been the cause of these characteristics, they would have ceased to be exclusive to man and would have appeared in other animals. Consequently, it was necessary to include another variable in the equation. Darwin was disappointed by this change of heart, which was the source of intense debate between the two naturalists.
THE SPIRITUAL ORIGIN OF MAN
In an attempt to follow Wallace’s arguments, we must turn our attention to the savage “races” and prehistoric man. In Victorian times it was generally admitted that the brain was the organ of the mind and that the development of the intellectual faculties was correlated with the size of the brain. Thus, European man, enjoying a larger brain than any other race, stood at the pinnacle of intellectuality and sensibility. In this sense, Wallace’s perspective was too advanced for his time, being far removed from racial prejudices: he pointed out that, although the brain volume of savage and prehistoric men was smaller than that of civilized individuals, it was only slightly smaller, whereas it was significantly larger than that of the great apes. This would explain why mental capacities are more refined in civilized populations and incipient in savages. Even so, although in these tribes animalistic behaviors predominate and their intellect is rudimentary, it is occasionally possible to observe the expression of the most outstanding and characteristic mental capacities of civilized man: religious sentiment, love, honesty, art. In these communities, therefore, the properly human faculties are in a latent phase. This indicated that intellect and consciousness would have been born prematurely in primitive man, at a stage of our evolution where they would have no adaptive function. However, without them, the human being would not have been able to reach his present level of development. Therefore, these characteristics would have appeared in order to guarantee our evolution and manifest themselves to their full potential in the future, thus violating the fundamental principles of evolution by natural selection. All this pointed to the fact that the structure and organization of the human brain exceed the real utility they should have. If it had developed by natural selection, the brain should not have been much larger than that of a gorilla or an orangutan, since with that volume it would provide the precise requirements to ensure our survival.
Discarding natural selection, the alternative pointed out by all this evidence is what Wallace identified with one or several Superior Intelligences that through their will could guide the action of the evolutionary laws with a specific purpose: to favor the development of the spiritual essence of man. Later on, Wallace would attribute the creation of the whole universe and the natural laws to these supreme entities as an indispensable premise for the development of progressively more advanced intelligences, thus configuring a theistic, finalistic and anthropocentric worldview. The whole universe was arranged to ensure the constant evolution of intelligence. It could be deduced, therefore, that the capacities of the human mind are not yet expressed to their full potential, waiting for the human being to reach a more advanced stage of development.
THE ANTI-VACCINE CRUSADE
Another aspect equally or more controversial than those already mentioned is his animosity towards smallpox vaccines. There was a time, however, when he considered vaccines as one of the greatest contributions of science and Edward Jenner, discoverer of the smallpox vaccine and father of immunology, as one of the most important benefactors for mankind. In fact, he and his children were vaccinated on several occasions.
We could summarize in two causes that led the naturalist to carry out a crusade against vaccines, as he himself baptized it. On the one hand, a marked feeling of social justice that stimulated his indignation against the laws that imposed compulsory vaccination in England. From 1840 onwards, the British Parliament enacted a series of regulations to administer smallpox vaccination programs. From 1853 vaccination became compulsory, resulting in punishments and penalties for those who refused vaccination. These penalties were not applied equitably, with the working classes suffering the heaviest fines and even imprisonment. This aroused popular indignation and distrust, which would eventually crystallize into the anti-vaccine movement, a response to the injustices and crimes against personal freedom. Interestingly, this movement attracted different groups whose common purpose laid in socio-political and philosophical criticism and social reformism. Thus, doctrines as apparently disparate as Spiritualism, vegetarianism, Swedenborgianism, antivivisectionism, or socialism found another form of expression in the antivaccine movement. Coincidentally, Wallace was a follower of many of them. Moreover, these doctrines brought an institutional identity to the antivaccine cause through the formation of leagues, meetings and mass debates.
The other essential element that promoted Wallace’s conversion was his meeting around 1880 with the businessman William Tebb, co-founder of the London Society for the Abolition of Compulsory Vaccination and, not by chance, also a follower of Spiritualism. Tebb introduced Wallace to the anti-vaccine movement through several literary works that apparently confirmed the reduced efficacy of vaccines to prevent smallpox and their role in the spread of the disease. He also promoted the publication of a small pamphlet written by the naturalist in 1885 and entitled Forty-five years of Registration Statistics, Proving Vaccination to be both useless and dangerous with the aim of warning Members of Parliament and the general public of the danger and ineffectiveness of compulsory vaccination programs. Thereafter, Wallace would launch an enthusiastic fight against vaccine advocates and the state’s interventionist and monopolistic public health practices.
How were vaccines defended or vilified? Proponents and detractors used the available data as a key argument for their own statistical explorations of the situation. Wallace, for example, prepared sophisticated graphs and calculated the vaccine efficacy over long time series using official data provided by different countries and the British General Register Office. The conclusions he reached could not have been more discouraging: the data could not support the link between vaccines and the reduction in smallpox mortality. On the contrary, the figures pointed to worrying increases in population mortality and in the severity of epidemics in relation to the increase in vaccination coverage and since vaccination became compulsory. Vaccines were, therefore, harmful, as they promoted disease rather than preventing it. Wallace was right to some extent actually. Some medical practices that were not very aseptic, such as the “arm to arm” method (consisting of extracting the vaccine from the pustules of a previously vaccinated individual), promoted the transmission of blood infections such as syphilis or hepatitis.
According to his understanding of the disease, it was impossible for vaccines alone to neutralize a complex pathogen that changes and evolves over time. According to the naturalist, the factors that determined the incidence and severity of smallpox were the hygienic-sanitary and nutritional conditions of the population. In his analysis of smallpox mortality in England (which included data from the middle of the 18th century up to his time), he was able to verify that, before the introduction of vaccines and compulsory vaccination campaigns, mortality from smallpox began to experience a progressive reduction. What was the cause? Undoubtedly, the implementation of improved sanitary and hygienic conditions. In this way, Wallace exposed vaccination programs as smokescreens that diverted attention from the real social problems that the State had to solve in order to really put an end to the nefarious disease.
Ironically, pro-vaccine advocates used the same type of reasoning and statistical tools to support their positions. However, according to them, the data unquestionably supported the success of vaccination campaigns. Who was right then? In retrospect, we would say that vaccines have been a fundamental tool for saving lives. Not surprisingly, on May 18, 1980, the absolute eradication of smallpox was announced, the first infectious disease to be eliminated worldwide, but we could also mention the virtual eradication of polio or the millions of people who have been spared measles or tetanus. However, if we have to assess the efficacy of smallpox vaccines in Wallace’s time without leaving that context, it would not be so easy. The scarcity of available data, the controversial way of collecting them, the subjective way in which each author divided the time series, or the lack of knowledge of fundamental covariates, such as the cyclical behavior of smallpox, resulted in subjective interpretations that were too biased to be able to draw anything clear.
THE NATURAL HARMONY
How is it that a person so closely linked to scientific materialism embraced with such vehemence such heterodox and marginal subjects? Undoubtedly, his life experiences contributed significantly. His early contact with nature, self-learning and his unparalleled ability to theorize and unravel natural patterns and processes would lead him to postulate the existence of a natural harmony that governed the universe at all levels. If a mechanism or phenomenon acted without violating this fundamental principle, there was no reason to reject it, as was the case with phrenology, mesmerism or Spiritualism. With this in mind, Wallace elaborated a personal definition of what science should be: the balanced and equitable connection between nature, politics, ethics, spirituality, and freedom. Anything that could disturbed this balance had to be stopped, as was the case with vaccines.
Logically, his metaphysical speculations were frowned upon by materialistic scientists, including his great friend Charles Darwin, who wanted to give science its own identity to make it independent of socio-political and spiritual issues. Perhaps it was for this reason that, with the passage of time, Wallace would end up being relegated to the background and relatively forgotten. However, to discredit him for these aspects of his personality is a crass mistake, a reduction to absurdity of a singular, complex and extremely brilliant mind like his. On the contrary, we must recognize him as one of the most admirable and innovative scientists in history, whose scientific contributions to understanding the mysteries of nature remain invaluable.
Did you know that Alfred Russel Wallace had a bitter confrontation against a flat Earth advocate and that with a simple experiment he proved the Earth’s curvature? In this article you can read this unusual episode in detail:
Fichman, M., Keelan, J.E. (2007). Resister’s logic: the anti-vaccination arguments of Alfred Russel Wallace and their role in the debates over compulsory vaccination in England, 1870–1907. Studies in History and Philosophy of Biological and Biomedical Sciences 38, 585-607. https://doi.org/10.1016/j.shpsc.2007.06.006
Gross, C. (2010). Wallace and the evolution of human mind. The Neuroscientist 15, 496-507. https://doi.org/10.1177/1073858410377236
Kottler, M.J. (1974). Alfred Russel Wallace, the Origin of Man, and Spiritualism. Isis 65, 144-192.
Scarpelli, G. (1992). “Nothing in nature that is not useful”. The anti-vaccination crusade and the idea of ‘harmonia naturae’ in Alfred Russel Wallace. Nuncius 7, 109-130. https://doi.org/10.1163/182539192×00055
Wallace, A.R. (1855). XVIII.—On the law which has regulated the introduction of new species. Annals and magazine of natural history 16, 184-196.
Wallace, A.R. (1858). On the tendency of varieties to depart indefinitely from the original type. Journal of the Proceedings of the Linnaean Society.
Wallace, A.R. (1870). The limits of natural selection as applied to man. Contributions to the Theory of Natural Selection: A series of essays. New York: MacMillan.
Wallace, A.R. (1875). On miracles and modern spiritualism: Three essays. London: James Burns.
Wallace, A.R. (1885). To Members of Parliament and others. Forty-five years of registration statistics, proving vaccination to be both useless and dangerous. London: E.W. Allen.
Wallace, A.R. (1898). The wonderful century: Its successes and its failures. Toronto: George Morang.
Wallace, A.R. (1905). My life: A record of events and opinions (Vol. 1). London: Chapman & Hall.
Wallace, A.R. (1905). My life: A record of events and opinions (Vol. 2). New York: Dodd, Mead & Company.
Wallace, A.R. (1907). Is Mars habitable? London: Macmillan and Co.
Weber, T.P. (2010). Alfred Russel Wallace and the antivaccination movement in Victorian England. Emerging Infectious Diseases 16, 664-668. https://dx.doi.org/10.3201%2Feid1604.090434soc