Nowadays, biology, and the life sciences more generally, are in magmatic development. Observational data and experimental results are obtained at a very fast pace, and are more and more precise and reliable, in all its branches (from molecular to evolutionary biology, from ethology to the neurosciences). More importantly, however, also on the theoretical side there is an ongoing lively debate. To use the well-known terminology of historian and philosopher of science T. S. Kuhn, it might seem that evolutionary biology be on the threshold of a “revolution”. An increasing number of authoritative scholars in the field enquire into the need of a substantial theoretical reconsideration potentially requiring a true “paradigm shift” in the near future. In brief, this is the topic of the special issue here proposed to our readership.
The first name coming to one’s mind when evolutionary biology is mentioned is the one of Charles R. Darwin. Rightly so: without his contributions one cannot imagine the development of the evolutionary approach to the living being. Thanks to Darwin’s work, evolutionary biology has reached a mature scientific status. Indeed, the Darwinian theory has a great explanatory power. The idea of natural selection makes sense of the fact of evolution – a fact already at that time supported by many paleo-ontological and archeological data as well as naturalistic observations (those done by Darwin himself around the globe included) showing the outstanding variability of life-forms even in a small environment. The case of the so-called “Darwin’s finches” is eloquent .
The evolutionary approach to life, however, does not begin with Darwin. We should go at least half a century before the publication of Darwin’s masterpiece in 1859 (On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life – this is the complete title of the “Origin”), to the year 1809, when Jean-Baptiste Lamarck published his Zoological Philosophy. Actually, moreover, a “historical”, indeed evolutionary conception of nature can be traced back almost to the time of Galilei. Nicholas Stensen (1638-1686), starting from his naturalistic studies (in geology and comparative anatomy), proposed the idea that nature – already the very geological conformation of our planet Earth – changes, it has a history, it does not remain unchanged in time. Of course, the idea of a “becoming” and that of history are much older, and can be traced back to the deep origin of Western culture: the Greek and the Judeo-Christian ones.
However, it is with Stensen that the idea of an evolving nature emerges in a properly scientific milieu. Lamarck will formulate the first evolutionary hypothesis about life (and – incidentally – will introduce the very term “biology”). Darwin will give to these developments their maturity with his evolutionary biology centered on the idea of natural selection. We are in the second half of the nineteenth century.
Let me propose a little comparison. Modern science – it is nowadays usually accepted – begins in the 16thand 17thcenturies. So-called “Copernican revolution” – i.e. the historical process from which modern physics emerges – conventionally opens in 1543, the year of (posthumous) publication of Copernicus’ De revolutionibus orbium coelestium, and symbolically closes with the publication of Newton’s Philosophiae naturalis principia mathematica in 1687. Now: does the history of modern physics end here? Obviously, it does not. It suffices to mention the two great revolutions in the physics of the twentieth century: the quantum and the relativistic ones – not to speak of the birth of thermodynamics and statistical mechanics, or electromagnetism and the “field physics”.
And: does the history of biology end with Darwin’s work? Patently, it does not. From a certain viewpoint, the special issue proposed here intends to stress this very point. It intends, that is, to stick around the changes in evolutionary biology after Darwin. More precisely, it intends to focus on the current changes in evolutionary biology – i.e. those novelties that have all the characters of “revolutionary” changes.
After Darwin, around the half of the twentieth century (about one century after the Origin), the so-called Modern Synthesis (or Neo-Darwinian Synthesis) stems from the works of scholars like T.H. Morgan, R. Fisher, T. Dobzhansky, G.G. Simpson ed E. Mayr. The Modern Synthesis is then “formalized” by the 1942 book by J. Huxley titled Evolution: The Modern Synthesis. The accomplished form of the Modern Synthesis has been elaborated in the sixties of the twentieth century, also because of the discovery of the DNA structure by Francis Crick and James Watson, in 1953.
Indeed, the main tenets of the Modern Synthesis in evolutionary biology can be summarized by saying that evolution procedes via:
- Variation production: mutations and genetic variability,
- Variation transmission: (Mendelian) genetic heredity,
- Variation selection: natural selection (“survival of the fittest”).
Now, this patently is not a “recent development”; it can be regarded as the “received view” of contemporary evolutionary biologists. However, the last 50-60 years have seen many developments, both empirical and theoretical. They cannot be considered here, but it will be interesting to stress that in the life-sciences scientific community there is a current lively debate between two main camps: those who claim that the Modern Synthesis still represents the reference theory in evolutionary biology – i.e. that Modern Synthesis still is a “healty research program”, to use the expression of another 20th century epistemologist, Imre Lakatos – and those who call for a deep rethink of that theoretical setting .
Which are the elements favoring such a rethink? Also in this case, it would be hard considering all the relevant points. Perhaps, however, the fundamental point for the Modern Synthesis (be it more or less explicitly perceived) is the notion that an organism possesses, stated in its DNA, a program mastering its development and ensuring it reaches its mature form. Such a program would thus determine the organism’s morphological, anatomical and physiological characters, as well as its behavioral and cognitive faculties. With this idea in place, the Modern Synthesis’ explanation of biological evolution was quite smooth and effective. The traits of an organism determine its survival and reproductive success. Natural selection rewards the organisms with the fittest traits, and thus favors the spreading of the genomes fixing those successful traits.
The so-called Extended Evolutionary Synthesis (EES) – i.e., the attempt at a new theoretical approach overcoming the Modern Synthesis – essentially puts in question this fundamental tenet of the “received view”. According to this new understanding, the organisms no longer are programmed by DNA. They are rather built up during development in ways that are extremely dependent on environmental factors and on features linked to the organism’s behavior and the interrelationships it entertains with other life-forms in its environment. Note that this is not a marginal point, as it has momentous consequences both upstream and downstream the action of natural selection.
Upstream, as the entity upon which the environment would act selectively would no longer be, according to the new view, the “direct product” of a certain genome, but the result of the array of interactions between the developing organism and its environment. Downstream, as the environment selectively acting on the organisms dwelling in it would no longer be, under the novel approach, “independent” of those very organisms, which on the contrary contribute substantially to fix the environmental factors and features.
In the Modern Synthesis the focus was on the genes, the genome. The environment was the selective factor. The role played by the real and concrete organism – apart from heredity – was mainly reduced to that of an interface between the inheritable genome and the selective environment. In the Extended Synthesis, instead, what happens in the real and concrete organism’s lifetime (its ontogenesis) has central relevance. The emphasis is on how the organism modifies its environment, changing, and very often buffering, the selective factors acting on it and its progeny (this is usually referred to as niche-construction). The emphasis is on how the environment modifies the organism during its lifetime (without requiring genetic mutations), inducing (new) morphological or behavioral traits and characters (this is usually referred to as “phenotypic plasticity”). At this point, the development of organisms is regarded as the main focus, the place where biological evolution really happens (and this is the core of the so-called evolutionary developmental biology – “evo-devo”).
Another revolutionary feature of the Extended Synthesis has to do with the modalities (or “channels”) of information transmission. According to the Modern Synthesis, heredity was genetic, without exceptions. The Extended Synthesis, instead, distinguishes at least other three transmission modes. The epigenetic one: the transmission of variations not through genetic mutation by thanks to changes in non-genetic (i.e. epi-genetic) molecular features. The behavioral one: an array of behaviors and survival strategies are passed on by means of social learning (imitation, emulation, etc. – essentially by copying other members of one’s group), and not thanks to genetic transmission. The symbolic one: great amounts of information are transmitted from generation to generation via symbolic communication (language and writing, monuments and artwork, etc.) – this is the case of culture in human evolution.
What touched on in the last four paragraphs might capture the key lines along which evolutionary biology is changing nowadays. Entering finer details is unfeasible here. In some sense, such a deepening may be triggered by the reading of the texts proposed in this special issue. However, before briefly introducing those documents, another consideration might by interesting to our readership. Some of the points inclining scholars in the field to propose an Extended Synthesis have to do with human peculiarities, specifically with culture and cultural evolution. Consider, for example, the issue of so-called gene-culture co-evolution, i.e., the idea that cultural strategies and innovations, being part and parcel of the selective environment of human populations having them, can indeed affect the genetic evolution of those populations. Well, this is a case of niche construction. Gene-culture co-evolution stemmed from the field of population genetics in the seventies of the last century: this gives an idea of how much culture as a “human factor” has influenced the ensuing research in evolutionary biology. Even clearer is the relevance of human culture for theorizing around the information-transmission modes: the abovementioned symbolic modality is at the heart of culture and cultural evolution.
Let us now come to the documents gathered in this special issue. They are arranged in a “quasi-chronological” order, though the first proposed reading is a recent chapter in a collected volume by Jean Gayon (1949-2018, French historian and philosopher of biology) that may serve as a general introduction to the broad topic of evolution theories. Gayon offers a readable overview of the history of evolution theories from Darwin’s original proposal through the developments of “Darwinism” in the ensuing one-and-a-half century.
The second document is a comment to Stensen’s Prodromus to a Dissertation concerning Solids Naturally Contained within Solids. This is the work where, as mentioned, Stensen clearly proposes the idea of a chronology of nature, the idea that nature actually has a real historical dimension. The title of the work appears to link more to geology than to biology, but it is not entirely so. The reader will discover that the solids considered by Stensen are not only rocks and sediments, but also fossils of living beings – i.e. the primary factual basis for biological evolution.
After that, we propose an excerpt from the fourth chapter of Darwin’s The Origin of Species. This chapter tackles with the issue of natural selection and, as natural selection is the core of Darwin’s theory of biological evolution, it will turn out to be helpful to read through the pages in which he formulated the idea influencing so much of the development in biology. For this reason, we chose to propose here the text of the very first edition of the Origin (1859).
A key text of this special issue is the last chapter of the book by Alfred R. Wallace titled Contributions to the Theory of Natural Selection. Wallace is the co-discoverer – along with Darwin, of course – of natural selection. In the chapter proposed here, the author expresses his doubts about the assumption that natural selection could effectively explain every aspect of human evolution. The book has been published in 1870, and should be appropriately contextualized in its age. Some of the arguments used there are no longer entirely adequate to the current developments in evolutionary biology. Also the “spiritualistic” perspective emerging from the text would nowadays receive strict criticisms. Nonetheless, the text is interesting from at least two viewpoints (beyond the purely historical interest). First, Wallace clearly states a problem (the one about the limits of natural selection in the case of the human being) that is a current widely discussed issue – not just in the field of “science and faith” but also in biology stricto sensu. This also bears relation with the more general ongoing “rethink” of evolutionary theorizing (which Wallace could not foresee, obviously). Secondly, Wallace chapter is an example of interdisciplinary speculation by a biologist/naturalist that might appear as totally extraneous to the work of a professional biologist nowadays (though it is not always so, indeed), but that certainly was not unknown to scientists working in Wallace’s time or earlier: think to the figures of George Boole (1815-1864) or of Augustin Cauchy (1789-1857), not to speak of Galilei and Newton.
To show how the problem pointed out by Wallace keeps being perceived in more recent times, the next proposed text is a Science paper by T. Dobzhansky and M.F. Ashley Montague addressing the very issue of the relationship between natural selection and the “mental capacities of mankind”. Of note that the text has been published, by one of the main scientific journals, in 1947 – i.e. in the period when the refinement of the Modern Synthesis was taking place (also thanks, as we saw, to the contribution of Dobzhansky himself).
The sixth proposed text is a Précis of the famous book Evolution in Four Dimensions (2005), by E. Jablonka and M.J. Lamb. The Précis has been published in 2007 by the authoritative journal Brain and Behavioral Sciences as followed by comments authored by many influential scholars in the field, and by an authors’ final reply. We propose here only the main text (with a short presentation). The paper is helpful as it introduces the main topics of the mentioned book, which is one of the works certainly spurring the process of theoretical rethink of evolutionary biology already mentioned more than once in this introduction.
The special issue closes with a very interesting Nature paper published in 2014 in which the voices of the supporters of the Modern Synthesis and those of the proponents of the Extended Synthesis are confronted point by point on key issues. This paper gives a clear impression that evolutionary biology is at the threshold of a paradigmatic revolution.
 The “Darwin's finches” are so called as they captured Darwin’s attention when he reached the Galapagos islands with the Beagle. The inter- and intra-specific variability of Galapagos finches is really astonishing. Moreover, more recent studies on those bird populations offer clearcut confirmation of the actual effectiveness of natural selection: P.R. Grant - B.R. Grant, How and why species multiply. The radiation of Darwin’s finches, Princeton University Press, Princeton – Oxford 2008. P.R. Grant, Ecology and evolution of Darwin’s finches, Princeton University Press, Princeton 19992.
 Cf. K. Laland – G. Wray, et al., “Does Evolutionary Theory Need a Rethink?”, Nature, 514 (2014): 161-164. (This paper is proposed as the last document in the present special issue.)