Wallace Arthur

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Wallace Arthur is a zoologist specialising in evolutionary developmental biology. He is Emeritus Professor of Zoology at the National University of Ireland, Galway. From 2004 to 2012 he was the Established Professor of Zoology at NUI Galway. Before that, he was Professor of Evolutionary Biology at the University of Sunderland, UK. He is one of the founding editors of the leading journal Evolution and Development, and has written several books on evolution, including one on the origin of animal body plans. He describes himself as "a bit of a maverick" who likes "making connections across disciplinary boundaries".[1] Arthur cites the three best books he has read as Darwin's (1859) On the Origin of Species, D'Arcy Thompson's (1917) On Growth and Form; and Lancelot Law Whyte's (1965) Internal Factors in Evolution.[1]

Amongst Wallace Arthur's earliest attempts at interdisciplinary conceptualisation was his 1987 book Theories of Life,[2] in which the influence of Arthur's three favourite books, amongst others, can be seen. In his 1987 book, he attempted to unite conceptually the fields of genetics, development, and evolution.[3] In this work, he addressed issues of relevance not only to evolutionary theory, but also to the philosophy of science, using evolutionary theory as the vehicle for this. He posed the questions of what constitutes a scientific theory, and how it is distinguished from hypotheses and laws. "One of the main distinctions between these different types of 'scientific idea', is the degree of certainty attached to it. A hypothesis is the least certain and is essentially a tentative answer to a particular question, often put forward so that it can be tested experimentally."[4] Arthur describes the hypothesis as being at the least certain end of a spectrum of scientific certainty.

At the other end of the spectrum of certainty/uncertainty is the scientific law. These sometimes come individually but more often in sets. An example of the latter is provided by the Laws of Thermodynamics, which are of central importance in physics, and indeed in science as a whole. (The first Law of Thermodynamics is better known by its alternative title, the Law of Conservation of Energy).[4]

To Wallace Arthur, "basically, a law is a universally accepted generalization. Usually, universal acceptance can be achieved in science only when very precise testing is both possible to conduct and positive in outcome when conducted: and precise testing is possible only when the assertion to be tested takes a quantitative form".[5] Thus, in the certainty/uncertainty spectrum, a hypothesis remains to be tested, and a law has generally been rigorously tested. Arthur notes that the categorisation of theories is more problematic.

Where does a theory fit in? The answer is, unfortunately, that it can fit in almost anywhere, and that its meaning is much more difficult to pin down than that of a hypothesis or law. On the one hand, theory can mean hypothesis, as it does in the phrase 'it's only a theory', meaning that an idea has not been adequately tested or that it has not been tested at all. On the other hand, in the Theory of Evolution we are referring to a process - evolution - which is almost universally accepted within the present-day scientific community and thus has almost the certainty associated with a law.[6]

Continuing on this theme, Arthur noted "two dimensions in addition to certainty/uncertainty...helpful in distinguishing between hypotheses, theories and laws":[6]

  1. "Degree of 'quantitativeness':- Most useful in distinguishing laws (e.g. Mendel's) from law-like theories (such as Darwin's)".[6]
  2. "Breadth:- Helps to separate hypotheses from laws and theories, because the former are usually quite specific while the latter two are usually broad".[6]

He elaborates thus: "Darwin and Mendel were ultimately making statements broadly applicable to all species in the living world, whereas the hypothesis that for example, high-fat diets cause heart-attacks in man is of relatively narrow applicability and would not, if proved to be true, turn into a law or theory".[6] Arthur notes that over time, if a hypothesis progresses from untested to tested, it cannot remain as a hypothesis. If refuted, "it is simply a refuted hypothesis' and disappears from the face of science".[7] If proved true, "it turns either into a theory or a law or, if it is too specific and limited to be either, a fact. A particular diet known to cause heart conditions is a fact". He notes also that "according to the philosopher of science Karl Popper, it is possible only do disprove a theory, not to prove it".[7]

A central theme to Arthur's 1987 book is the morphogenetic tree, which he expounds in chapter ten, The Missing Theory of Development.[8] Arthur's morphogenetic tree essentially is not unlike an evolutionary tree,[9] and the resemblance "may not be merely coincidental".[10]


  • Mechanisms of Morphological Evolution: 1984, Wiley
  • Theories of Life: Darwin, Mendel and Beyond: 1987, New York, USA & Harmondsworth, UK publisher Penguin, ISBN 0-14-022699-0
  • A Theory of the Evolution of Development: 1988, Wiley
  • The Origin of Animal Body Plans: 1997, Cambridge University Press
  • Biased Embryos and Evolution: 2004, Cambridge University Press
  • Creatures of Accident: The Rise of the Animal Kingdom: 2006, Hill & Wang (Farrar, Straus & Giroux)
  • Evolution: A Developmental Approach: 2011, Wiley-Blackwell
  • Evolving Animals: 2014, Cambridge University Press


  1. ^ a b Ross, Greg (n.d.), "Scientists' Nightstand: Wallace Arthur", American Scientist Online (Sigma Xi: The Scientific Research Society), archived from the original on 2008-08-28, retrieved 3 November 2010 
  2. ^ Arthur, Wallace (1987), Theories of Life: Darwin, Mendel and Beyond, New York, USA & Harmondsworth, UK: Penguin, ISBN 0-14-022699-0 
  3. ^ Glass, Bentley (June 1988), "Reviewed work(s): Theories of Life: Darwin, Mendel and Beyond", Quarterly Review of Biology 63 (2): 208–210, doi:10.1086/415848, JSTOR 2831009 
  4. ^ a b Arthur (1987), p.23
  5. ^ Arthur (1987), pp.23-24
  6. ^ a b c d e Arthur (1987), p.24
  7. ^ a b Arthur (1987), p.25
  8. ^ Arthur (1987), pp.119-142
  9. ^ Arthur (1987), figure 17, p.131
  10. ^ Arthur (1987), p.132

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