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I cannot anyhow be contented to view this wonderful universe, and especially the nature of man, and to conclude that everything is the result of brute force. I am inclined to look at everything as resulting from designed laws, with the details, whether good or bad, left to the working out of what we may call chance. Not that this notion at all satisfies me. I feel most deeply that the whole subject is too profound for the human intellect.
Letter from Charles Darwin to Asa Gray, May 22, 1860
The publication of On the Origin of Species by Charles Darwin in 1859 was one of the greatest milestones in the history of Biology. This work received a warm welcome on the part of many scientists but also caused great controversy. The controversy was principally surrounding its ideas that the living world was governed by chance and material forces, instead of being guided by a Divine Plan as William Paley did in his 1802 work Natural Theology. The astronomer Sir John Herschel, for example, referred to Darwin's theory as “the law of higgledy-piggledy” (the law of disorder), referring to the importance of chance presented therein.
From that moment on, the philosophy of nature had to confront new challenges particularly related to the problem of naturalism and finality. One of the principal questions refers to whether there was or not a plan guiding evolution: that is to say, if evolution relates to a blind succession of events, or if it is a process that tends towards certain ends. The main argument of those who deny the existence of an end in evolution is the presence of chance.
In the introductory passage cited, Darwin says that he feels inclined to see this wonderful universe as the result of laws and chance, although he later adds that this notion does not appear to be completely satisfactory. Throughout this study we will seek to clarify the causes of Darwin’s “dissatisfaction” with respect to the conception of a nomological design open to the incidence of accidents
During the 150 years that have passed since the publication of On the Origin there have been made multiple interpretations related to the role of chance in evolution. More than a few people have had a vision of evolution as purely random, as if it were a blind process with neither direction nor finality. Recent scientific research has shown that there is still much to learn from Nature, and phenomena than previously were thought to be stochastic are not. Despite this, it is still common the conception that evolution is a “casual” (random) process whose results are totally unpredictable.
One example of this are the discussions about the supposed incompatibility of the theory of evolution with the fact that living beings, including man, are part of a Divine project. On the one hand we find those who contend that the random character of the evolutionary process requires that all of its results are absolutely contingent, so that if, for example, an asteroid had not struck Earth over 65 million years ago our species would never have existed. Thus, if we are here it by cheer luck and not because of Divine design.
On the other hand, some people of faith respond to the “dethronement of man” by taking a hostile attitude towards science or, at the least, towards Evolutionary Biology. Poorly named “creationists” promote a literal interpretation of Genesis, while others, such as proponents of the Intelligent Design, claim to see in what science has yet to explain the indication of God’s direct intervention, rejecting the possibility that natural causes for said phenomena can be found in the future. In such discussions we find a basic problem: considering biological evolution as a process which, in the absence of direct intervention from God, fails any kind of finality.
The objective of this study is to address two related questions: (1) the belief that evolution is a process eminently driven by chance, and (2) that it is lacking in finality and, as such, its results cannot be part of a Divine project. Considering evolution as such gives chance a central role in the evolutionary process and leads many to a reductionist interpretation of the presence of chance in said process.
We assert that Darwin has had an enormous influence on this casual vision of evolution, not only for the central role he gave to chance in his hypothesis, but also for how he understands its role in the evolutionary process. For this reason, we studied the position that the English naturalist had, analyzing what causes he believed intervened in evolution.
In addition to the study of his most important writings, we pay particular attention to his correspondence. Darwin, much like other scientists of his time, made extensive use of correspondence to exchange ideas with colleagues. In these letters we see his most profound convictions and the dilemmas that do not appear so clearly in his published works.
Although Darwin failed to develop in a systematic way the concept of chance and causation in On the Origin of Species, little by little his treatment of these notions became more profound thanks to the intense correspondence he held with an eminent Harvard professor, the botanist Asa Gray. Gray rapidly accepted the theory of evolution and played a decisive part in its acceptance in the United States, even though he did not share Darwin’s emphasis on the “causal” character of variations.
One of the central themes in the almost 300 letters exchanged between Darwin and Gray we studied is “design,” which for them referred to the compatibility between the mechanism proposed by Darwin and the existence of a Divine plan in evolution. Surrounding this problem, Darwin and Gray formulated with more precision their vision of chance, the causes of evolution, contingency and the laws of nature.
We analyzed what concept Darwin and Gray had for the causal action on evolution and what role they attributed to chance. Despite the fact that both were naturalists and not philosophers, the discussions we will analyze can be sorted into the three branches of philosophy: the philosophy of nature, the philosophy of science and natural theology.
Although history occupies an important part of this work, its focus is not only historical but also metaphysical. Concretely, we have analyzed these questions in light of classical Aristotelian philosophy, as this Greek philosopher not only was the first to systematically study the concepts of chance and causation, but also studied biology closely from a metaphysical perspective.
For this reason, in the first chapter we will carefully study the thinking of Aristotle with regard to the notions most relevant to our study: causality, chance, nature, the soul and necessity. Finally, we will see how he integrated all of these concepts in his biological works, which comprise more than a fourth of his writings.
The second chapter will be a study of the influence Newton and Herschel had on the formation and thinking of Darwin with respect to the causes, and in concrete the concept of the vera causa that Herschel made popular in British science in the nineteenth century. We will also look at the way in which this concept influenced the work of Darwin and how the Darwinian theory was received by of the scientific community and by Herschel himself.
In light of the fact that the discussion between Darwin and Gray is strongly related to what it is called “the argument of design,” in the third chapter we will consider the principal currents in natural theology in England in the nineteenth century, and the development of the idea of design that Darwin had up until the moment that On the Origin of Species was published.
In the fourth chapter we will assess the way Asa Gray helped to foster the positive reception of Darwinism in the United States. We will also analyze some of the articles he published about Darwin’s book in 1860 and the beginning of his dialogue with Darwin regarding the question of design. Thus, we can observe how Gray emphasized the compatibility between Darwin’s theory and Christianity, while Darwin emphasized the impossibility to see a Divine project in evolution.
In the fifth chapter we will address how the debate developed, analyzing two works in which Darwin showed Gray the existence of “accidents” in evolution, that is to say, variations which –according to Darwin– could not be part of an “intelligent” plan. We will also see the way in which Gray changed his position after 1874, as it is reflected in his essay published in 1876 and two conferences given to theology students in 1880 at Yale.
In the sixth chapter we will see some recent interpretations of the role of chance in evolution and reflect on how a metaphysical understanding of chance and causation in evolution can help to overcome some of the problems identified.
Sources and translations
We used Darwin’s correspondence available on the Darwin Correspondence Project (http://www.darwinproject.ac.uk) of Cambridge University, wherein we find the majority of Darwin’s letters published since 1985. For each letter we indicate a number (entry) that appears in the Catalogue of correspondence adopted by the Darwin Correspondence Database (DCD). Darwin’s works were referenced using the versions available on Darwin-Online (http://darwin-online.org.uk) as it is fundamental in many cases to use the exact edition related to the issues addressed by Darwin and Gray.
We refer to the works of Aristotle using a range of English, Spanish and Italian translations. In cases where there are different interpretations of the same text, we refer to the original Greek for the purpose of greater precision. As such it was an arduous task, but well worth the effort.
All of the translations are ours and we intend to be the most faithful possible to the original meaning, placing precision above elegance. Italics and numbering within citations are also ours – unless indicated to the contrary.
Finally I would like to thank all of the people who have made this study possible. In a particular way, I wish to recognize Professor Rafael A. Martínez for his immense support in these three years of work. I also appreciate the valuable comments and suggestions of Professors Phillipe Dalleur and Ruben Pereda.
«Da parte mia sono profondamente grato ai miei genitori d’avermi messo al mondo. E gratissimo sono al Padreterno perché non m’ha fatto nè peggiore nè migliore di quello che sono. Io volevo essere esattamente così come sono. Diverso di così mi andrei largo o stretto» (Giovannino Guareschi).
 Darwin Correspondence Database (DCD), University of Cambridge, entry 2814.
 Cfr. Stephen Jay Gould, “The Evolution of Life on the Earth”, Scientific American 271 (1994), 90; cfr. íd, Wonderful Life: The Burgess Shale and the Nature of History, W. W. Norton, New York 1989.
 Thanks to the Darwin Correspondence Project we have access to more than 7000 letters written or receved by Darwin, and we have some informationy about other 8000 letters.
 Frederick Burkhardt, et al (eds.), The Correspondence of Charles Darwin, Cambridge University Press, Cambridge 1985–.