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Metafore migranti e crescita della comunità scientifica: il caso dei paesaggi evolutivi
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We start defining a landscape as a function of multiple variables and show how this can be interpreted as a dynamical system. From the perspective of dynamical systems modelling, we move to analyze Waddington’s ‘epigenetic landscape’ and landscape representations in current developmental biology literature. Then we delve into the problem of models and metaphorical representations in science, which stands out as a crux for assessing the use of landscapes in development, and analyze the somehow parallel stories of Wright’s and Waddington’s landscapes. We conclude with some ideas on developmental landscapes in the context of visualization in science, with a focus on theoretical work in developmental biology.
The concepts of adaptive/fitness landscapes and adaptive peaks are a central part of much of contemporary evolutionary biology;
the concepts are introduced in introductory texts, developed in more detail in graduate-level treatments, and are used extensively
in papers published in the major journals in the field. The appeal of visualizing the process of evolution in terms of the
movement of populations on such landscapes is very strong; as one becomes familiar with the metaphor, one often develops the
feeling that it is possible to gain deep insights into evolution by thinking about the movement of populations on landscapes
consisting of adaptive valleys and peaks. But, since Wright first introduced the metaphor in 1932, the metaphor has been the
subject of persistent confusion, from equivocation over just what the features of the landscape are meant to represent to
how we ought to expect the landscapes to look. Recent advances—conceptual, empirical, and computational—have pointed towards
the inadequacy and indeed incoherence of the landscapes as usually pictured. I argue that attempts to reform the metaphor
are misguided; it is time to give up the pictorial metaphor of the landscape entirely and rely instead on the results of formal
modeling, however difficult such results are to understand in ‘intuitive’ terms.
In the English-speaking tradition of philosophy of language it has generally been taken for granted that the ideal rational language is literal and univocal and has a unique relation to truth. Its relation to the real world is atomistic, that is to say, small portions of language, whether words, phrases, or sentences, attach themselves to the world by some kind of correspondence or truth conditions, in a way that is essentially independent of linguistic context. The presence of metaphors and other tropes in language is a deviation from rational sense. As Hobbes put it, “such speeches are not to be admitted”, and metaphors are abuses of speech by use of words “in other sense than that they are ordained for; and thereby deceive others”. Literal language in its relation to truth is held to be the proper vehicle for science; it permits objective, testable, piecemeal accumulation of knowledge and expression of belief. Metaphoric language on the other hand is ambiguous, holistic in meaning and context-dependent, and in this view fit only to express subjective attitudes and emotions.
Excerpt
It would seem altogether fitting that this year's symposium be devoted to a consideration of the evolutionary theory. We are celebrating the one hundredth anniversary of the publication of Darwin's Origin of Species and the occasion of such a centenary is the proper moment to review the past and consider the future. It is almost universally recognized that no other theory has had as vast an impact on biology as the theory of evolution, emphasizing as it does that no organic being can be fully understood except by considering its history. Whether we are dealing with structures, functions or habits, individually or in their interactions, their understanding is one-sided and partial without a consideration of the historic processes that brought them into being.
The history of the first one hundred years since the publication of the Origin of Species is a fascinating one. With its many controversies, its false starts...
The adaptive landscape is an important diagrammatic concept that was conceived in population genetics. During the Modern Synthesis, in the first half of the twentieth century, the landscape imagery was used to represent evolution on a large scale, aiding in the construction of a common language for a new evolutionary biology. Not only historic adaptive landscapes by Dobzhansky, Simpson, and others are a record of how macroevolution was thought of in those decades; they stimulate reflection on “combination spaces” that underlie them. In fact, any landscape diagram is the three-dimensional transposition of a multidimensional space of combinations of genes, morphological traits, or other kinds of variables. This is an important and enduring general point of awareness: The diagram displays some aspects of the considered space while hiding others, exposing the author and the user to incomplete understanding and to conflating different spaces. Today, macroevolution is studied as a multifarious exploration of spaces of possibilities of all different sorts, interconnected in complex ways: genotype spaces, molecular spaces, morphospaces, geographical spaces, ecological spaces, and genealogical spaces. Actual macroevolutionary stories and outcomes are a subset of the universes of possible combinations—of genes, nucleotides, morphological traits, and environmental variables. Visualizations of macroevolution are a challenge of showing both distinction and correlation between spaces of possibilities.
According to Pigliucci and Kaplan, there is a revolution underway in how we understand fitness landscapes. Recent models suggest
that a perennial problem in these landscapes—how to get from one peak across a fitness valley to another peak—is, in fact,
non-existent. In this paper I assess the structure and the extent of Pigliucci and Kaplan’s proposed revolution and argue
for two points. First, I provide an alternative interpretation of what underwrites this revolution, motivated by some recent
work on model-based science. Second, I show that the implications of this revolution need to carefully assessed depending on question being asked,
for peak-shifting is not central to all evolutionary questions that fitness landscapes have been used to explore.
It is evident how much Olby and Provine have contributed to a better understanding of the emergence of genetics. It is equally evident, I believe, how many obscure issues still remain to be elucidated. Indeed, their volumes have raised as many new questions as they have answered old ones. In particular, the role of constructive as well as retarding contemporary concepts in the development of new generalizations still requires far more analysis. The somewhat independent trends of various national schools and the influence of neighboring fields (e.g. statistics, animal husbandry, systematics) are other areas deserving further study. All these influences contributed, one way or another, to the growth and maturation of genetics.37
Sewall Wright introduced the metaphor of evolution on “adaptive landscapes” in a pair of papers published in 1931 and 1932.
The metaphor has been one of the most influential in modern evolutionary biology, although recent theoretical advancements
show that it is deeply flawed and may have actually created research questions that are not, in fact, fecund. In this paper
I examine in detail what Wright actually said in the 1932 paper, as well as what he thought of the matter at the very end
of his career, in 1988. While the metaphor is flawed, some of the problems which Wright was attempting to address are still
with us today, and are in the process of being reformulated as part of a forthcoming Extended Evolutionary Synthesis.
Making Sense of Evolution explores contemporary evolutionary biology, focusing on the elements of theoriesâselection, adaptation, and speciesâthat are complex and open to multiple possible interpretations, many of which are incompatible with one another and with other accepted practices in the discipline. Particular experimental methods, for example, may demand one understanding of âselection,â while the application of the same concept to another area of evolutionary biology could necessitate a very different definition. Spotlighting these conceptual difficulties and presenting alternate theoretical interpretations that alleviate this incompatibility, Massimo Pigliucci and Jonathan Kaplan intertwine scientific and philosophical analysis to produce a coherent picture of evolutionary biology. Innovative and controversial, Making Sense of Evolution encourages further development of the Modern Synthesis and outlines what might be necessary for the continued refinement of this evolving field.
On the origin of species by means of natural selection. London: John Murray, sesta edizione 1872. Trad. it. L’origine delle specie
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Tropical talk: the myth of the literal
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Adaptive landscapes: a case study of metaphors, models, and synthesis in evolutionary biology
- E Serrelli