Despite the opinion of those contemporary scientists who believe philosophy is nothing more than an occupation for tired scientists at the end of their career – what is ungraciously known as the “philosopause” –, many of the greatest philosophers of all time were influenced by the scientific world-views of their day, and some of them, such as Descartes and Leibniz, made important scientific contributions of their own too. In other words, the fact that philosophy has long been intertwined with natural sciences should not be surprising, because philosophy has always been dealing with questions about the nature of the universe and our knowledge of it, aiming at an overall picture of what the world is like and how we fit into it, and these are matters on which science also has much to say. The emergence of modern science in the 17th and 18th centuries led to the colonization of parts of philosophy, so that many issues traditionally addressed by philosophers began to be surrendered to the scientists. But the above-mentioned event did not bring about the end of philosophical research; indeed, in the early years of 20th century, a new kind of philosophical inquiry arose, one that asks questions about the methods of science itself. Can experiments ever prove that a scientific theory is true? Can we rationally choose between two scientific hypotheses both fitting the available data? Can science ever reach an ultimate set of fixed laws? The study of such questions – which are not the exclusive preserve of philosophers – is crystallized into an academic discipline in its own right, known as philosophy of science.
Philosophy of biology is a sub-branch of the philosophy of science which emerged in 1970s and has grown rapidly since. Samir Okasha’s book – Philosophy of Biology. A Very Short Introduction, edited by Oxford University Press in 2019 – introduces the discipline in a way that does not presume specialist knowledge, being also a precious compendium of the main conceptual issues that arise within biology. The book consists of seven reliable chapters written in a fascinating and comprehensible style; in fact, Samir Okasha has the clarity of thought that comes from a flawless expertise in philosophy of biology and this allows him to offer crystal-clear explanations of its issues. The structure of the volume is as follows. Chapter 1 is a general introduction to the discipline. Chapter 2 outlines the theory of evolution by natural selection, explaining its philosophical significance. Chapter 3 focuses on the concept of biological function. Chapter 4 examines the problem of the levels-of-selection, which asks whether natural selection acts on genes, individuals or groups. Chapter 5 discusses biological classification and the question of the species. Chapter 6 examines philosophical issues in genetics. Chapter 7 asks whether human behaviour and culture can be explained in biological terms, examining the implications of biology for humans.
But what are the factors behind the emergence of such a discipline? Firstly, as Okasha suggests, “it became clear that traditional philosophy of science was too physics-centric – biology had been left out of the picture” (p. 2). Actually, in the early to mid-20th century, logical empiricism was the dominant school in philosophy of science, and logical empiricists like Rudolf Carnap, Hans Reichenbach and Carl Hempel developed a picture of science which took physics as its model. To put it otherwhise, they emphasized the role of the laws of nature – principles that underlie observed phenomena –, “[characterizing] scientific inquiry as the search of such laws, and scientific explanation as the deduction of phenomena from the laws” (p. 2). Unfortunately, while this picture applies quite well to physics, it applies less well to biological sciences, where we can find an abundance of empirical facts and a wealth of theories that are used to explain them, but no laws of nature from which those facts can be deduced. So, “the philosophy of biology arose partly out of a perceived need to redress this imbalance” (p. 4). Secondly, Okasha continues, the 20th century witnessed great advances in the biosciences – for example, the integration of Darwin’s theory of evolution with Mendelian inheritance, the emphasis shifted to the study of the molecular basis of living organisms and their cellular components, and the discovery of the structure of DNA by James Watson and Francis Crick in 1953 – culminating in the study of modern genomics. Philosophers became acquainted with these scientific results late, but as they caught up on all these improvements they immediately discovered a lot of interesting conceptual issues. To take one example, genetics researchers regularly use concepts borrowed from human communication systems, such as “coding”, “information” and “translation”. In this regard, “why does informational language permeate genetics, and what does it mean? Should it be taken literally, or is it just a metaphor?” (p. 5). Lastly, the third factor behind the rise of philosophy of biology was the move made by Anglophone philosophy to naturalize philosophical enquiry by trying to integrate it with empirical science, following Darwin’s quote that “he who understands baboon would do more towards metaphysics than Locke” (Ch. Darwin, Notebook M, 1838). One example of this shift is Ruth Millikan’s philosophical attitude; indeed, in the 1980s, she suggested a solution to the problem of intentionality by drawing on Darwinism. In short, “Millikan’s idea is that representational content may be rendered scientifically respectable by reducing it to biological function, a notion which plays a bona fide role in evolutionary biology” (p. 7). This is definitely a controversial attempt, but it clearly shows how a biological issue can throw light on an old philosophical problem.
The story Okasha tells us begins with the description of the Darwinian theory, which marked a turning point in our understanding of the natural world. Darwin’s central claims were three; species are not fixed but rather change their characteristics over time, current species have descended from one or a few common ancestors, and natural selection is the main means of evolutionary modification. What did Darwin mean by natural selection? As Okasha puts it, “Darwin meant the preservation of those organisms in a population who are best able to survive and reproduce in the environment, and the elimination of others” (p. 9). This way, natural selection would gradually adapt organisms to their environment, eventually giving rise to new life forms. But what is the real nature of natural selection? It is often described as a filter; once variations have arisen, a few are kept while others are lost. A process of filtering cannot create anything, and assumes the existence of the things being filtered. So, is it a mistake to think that selection can have something like a creative role in evolution? The view that Darwin discovered a purely negative factor has been expressed often – an early example is Hugo de Vries, a biologist at the turn of the 20th century. In other words, it seems that selection has no role in origin explanations, as selection can sort only things that already exist. In contrast, the philosopher of science Peter Godfrey-Smith has argued that selection is essential to many origin explanations in a way that does give it a creative role in the evolutionary process. As he puts it, “selection is not an immediate, or proximate, cause of a new variant, [but] natural selection can reshape a population in a way that makes a given variant more likely to be produced by the immediate sources of variation than it otherwise would be. As selection changes the background in which mutation and recombination operate, it changes what those factors can produce” (P. Godfrey-Smith, Philosophy of Biology, Princeton University Press, Princeton 2014, p. 39). Such a disagreement is just one example of the debate regarding the nature of natural selection. Then, Okasha goes on examining the version of the design argument due to William Paley and Darwin’s objection that “the continual preservation of the best variants in a population, and the elimination of others, creates the appearance of design in nature” (p. 13).
Another striking feature of the biological sciences is their regular appeal to the notion of function – this marks an interesting contrast with the non-biological sciences, where talk of function is virtually non-existent. Astronomers do not talk about the function of planets, while biologists often make statements in which the notion of function occurs; for example, “the function of the human kidneys is to cleanse the blood”. In this regard, “why do biologists make such liberal use of function-talk, and what exactly does it mean?” (p. 27). This question leads us straight to the two most popular philosophical analysis of function-talk in biology; the aetiological theory of function and the causal role theory. On the one hand, we have a theory that holds that the function of a biological item is to be identified with the effect of the item in virtue of which natural selection favoured it, on the other hand we have a theory that argues that the function of some part is simply its contribution to the operation of the overall system, which enables the system to do what it does. As Okasha writes, “the aetiological theory emphasizes that function attributions are often answers to the ultimate question ‘why does it exist?’ (Why does the cactus have spines? To deter herbivores). The causal role theory, by contrast, draws attention to a proximate question, namely ‘how does it work?’ (How does the immune system eliminate pathogens? By means of T and B cells, which kill intruders and produce antibodies)” (p. 36).
Further on, Okasha faces one of the most fundamental issue in evolutionary biology, the question of the levels of selection. In the typical Darwinian explanation, the process of natural selection which explains a trait’s evolution takes place at the level of the individual organism – this could also be expressed by saying that the unit of selection is the individual. To put it otherwhise, “it is the differential survival of individual […] – the fact that some do better than others – that leads to the evolutionary change” (p. 45). But theorically speaking, at least, there are other possibilities; indeed, below the individual we find entities such as cells, chromosomes and genes, and above the individual itself we find entities such as families, colonies and species. Hence, the author examines the opinion of those biologists who invoke group selection to help solve the so-called “puzzle of altruism” in nature and the objections raised to their position by George C. Williams. In fact, “his concern was with a widespread tendency among biologists at the time to think of adaptation in terms of group rather than individual benefit, often without realizing that individual selection will not necessarily produce group-beneficial outcomes” (p. 49). Williams’s key point is that a good explanation must show why the burrowing behaviour, and the physiology that allows it, is beneficial for the earthworm itself, not for some larger collective such as the ecosystem. But if group selection does not explain how altruism can evolve, then what is? This problem leads Okasha straight to kin selection, one of the most celebrated ideas in the 20th century evolutionary biology. In short, if altruists help their biological relatives rather than randomly chosen population members, and if altruism has a genetic basis, then natural selection can lead altruism to evolve. A generation of evolutionary biologists thought that group selection is a problematic concept while kin selection is acceptable. However, times have changed. Now, “many contemporary biologists argue that kin and group selection are not rivals but are actually equivalent, for they represent different perspectives on the same underlying biological process” (p. 54). At the end of Chapter 4, Okasha also takes into account the gene-centric view of evolution defended by Richard Dawkins, according to which the real evolutionary action takes place at the level of the gene – so that selection and adaptation would be best thought about at this level.
Previously, we have seen that above the individual we can find the species. According to the Linnaean system – which is traditionally used by biologists to classify the organism, having survived the transition from a creationist to an evolutionary worldview – each individual is assigned to a species. Moreover, “each species is assigned to a genus, each genus to a family, each family to an order, each order to a class, each class to a phylum, and each phylum to a kingdom” (p. 64). In this regard, while species is thus considered the base taxonomic unit, genera, families, orders, etc. are known as “higher taxa”. But how should organisms be assigned to species? Classification in science raises a deep philosophical issue, for all objects can be classified in more than one way. So, how should we choose between different ways of classifying? Are all classification schemes ultimately arbitrary? Okasha shows that competing definitions of species abound, and he also clearly illustrates that such a disagreement has practical consequences, for it means that biologists will frequently disagree about how many species a particular taxon actually contains.
In Chapter 6, the author introduces one of the best-known entities that biologists talk about, the gene, and starts asking what exactly is a gene. Somewhat surprisingly, “given the prominent position of genetics within the biosciences” (p. 83), there is no satisfactory one-line answer to this question. Why a precise definition is elusive? The reasons of this elusiveness are particularly interesting, raising a wealth of philosophical subtleties. To help the readers understand them, Okasha also delves into the history of genetics, presenting Mendelian, classical and molecular genetics – and this brings up another question too; how does the gene of Mendelian or classical genetics relate to the gene of molecular genetics? One common-sense answer is that the hypothetical entity which Mendel and the classical genetists posited to explain the available data turned out to be the same entity – namely a segment of DNA that codes for a protein. In other words, “although there are two different gene concepts – Mendelian and molecular – these concepts pick out the very same object in the world” (p. 92). This answer is not unreasonable, because the idea that a single scientific term may continue to refer to the same object despite considerable changes in associated scientific beliefs is standard in philosophy of science. As Okasha states, “the suggestion that the Mendelian gene is identical to the molecular gene goes hand-in-hand with the idea that Mendelian genetics can be reduced to molecular genetics” (p. 92). Unfortunately, despite its initial plausibility, this reductionist suggestion has been largely rejected by philosophers of biology. For example, an early objection was raised by Philip Kitcher. According to him, the explanation why Mendel’s law of segregation holds is cytological or cell-level, and not molecular-level. So, it does not seem true that molecular genetics explains the law of segregation. Even if we set aside Mendelian genetics and focus just on molecular genetics, the question of what a gene consists in is still not straightforward, because it has turned out to be an imperfect approximation to reality. In this regard, Okasha satisfactorily examines the sources of the problem, such as the gene regulation and the phenomenon of alternative splicing. Nonetheless, practicing geneticists’ day-to-day research appears to proceed smoothly without the need to legislate on exactly what is a gene. In this respect, the author makes an interesting remark; “according to one popular view, scientific knowledge is distinguished from everyday knowledge by its greater precision. It is natural to think that [the experimental precision of molecular genetics] should go hand-in-hand with conceptual precision. [But] the case of genes shows that this is not always so” (p. 97).
Finally, Okasha faces the question whether biology can shed light on humanity and its achievements. Can human behaviour be understood in biological terms? Does human behaviour depends more on social norms and cultural expectations than on genes? Some point out that the human mind is an evolved organ and that human behaviour – no less than animal behaviour – has been shaped by natural selection. Others accept that humans are evolved but argue that our species have largely transcended its biological nature. Perhaps, if we take a pragmatist anti-dichotomic approach, the terms of such a debate may be questioned; indeed, “given that human behaviour is the result of multiple causal factor” (p. 102), we can argue that the dichotomy between biological and non-biological explanations is untenable. Then, the author deals with the so-called “nature vs. nurture” debate – which asks whether inherited or environmental factors make us what we are. At the end of Chapter 7, he also introduces both the discipline of sociobiology and the discipline of evolutionary psychology.
One of the best summary of what philosophy is up to was given by Wilfrid Sellars, who wrote that philosophy is concerned with how things in the broadest possible sense of the term hang together in the broadest possible sense of the term. As philosophy does, also science tries to work out how things hang together, both disciplines having as a goal to build – or to discover, if we prefer a more Platonic overture – a general framework of our reality. In its relation to science, “philosophy has often also functioned as an “incubator” of theoretical ideas, a place where they can be developed in a speculative way while they are in a form that cannot be tested empirically” (P. Godfrey-Smith, Philosophy of Biology, cit., p. 1). Therefore, this means that philosophical reflection on biology has a valuable role to play; as Okasha puts it, “by scrutinizing the meaning of biological concepts, studying the implication of biological theories, and probing the logic of biological explanations, philosophy helps to deepen our understanding of the worldview painted by modern biology” (p. 117). In conclusion, Okasha’s book is an accessible, lucid and concise introduction to one of the most vital fields in contemporary philosophy, being the best starting point for anyone interested in exploring the new theoretical frameworks and controversies that are emerging in the above-mentioned discipline.