The following article is a draft of a review by Paul R. Gross of Freaks of Nature: What Anomalies Tell Us about Development and Evolution, by Mark S. Blumberg. The review will be published in Reviews of the National Center for Science Education.
An important subtext of Freaks of Nature, by the developmentalist Mark S. Blumberg, is the central importance, indeed the necessity, of monsters. To appreciate them is important, the argument goes, not only for progress in developmental biology, but also for solving the most challenging contemporary problems of evolutionary mechanism. A concomitant of this subtext is pleadings for an unmistakably more positive view, at least within those two sciences, of monsters and – as per the title – freaks of nature.
The original meanings of “monster” implied no disparagement: our word derives from the Latin monstrum – an unusual, unexpected occurrence that carries – for that reason – a message from the gods. Of course the term has evolved; it has acquired additional meanings including some that express revulsion. The latter reflect the common human responses to departures from the ordinary. Still, we may well object to the disparaging uses of “monster,” surely in speaking of humans; and so to object is probably humane. The plea to resist ignorant derogation of freaks, stated or implied, is ubiquitous in Freaks of Nature. And who can deny it?
The book has, however, a purpose more important than that display of humane sensitivity. It is, in fact, to present insights from evolutionary developmental biology, now well established within the life sciences as evo-devo. The insights offered derive from a putatively new understanding of the real significance of monsters, said to have been unrecognized, or – worse – ignored, after the triumph of the modern synthesis so-called, of genetics with comparative morphology and paleontology, under the driving force of successful Darwinian selection theory. The author refers to the “limitations of the modern synthesis” and suggests that the eventual reintegration of development (embryology in the first instance) with evolution has removed, or is well on the way to eliminating, the major flaws of the modern synthesis. A major rectification, that is, of Darwinism.
What were those flaws? Gradualism, “pan-adaptationism,” gene-centeredness – that is, those purported deficiencies of standard evolutionary theory that followed (mostly) the rapid domination of evolutionary biology, in the first decades of the twentieth century, by genetics. In short, the maladies of contemporary evolutionary theory to be cured by evo-devo, according to the author, are those, among others, that were identified in the 1970s and thereafter by such critics as Stephen Jay Gould and Richard Lewontin (in their famous “Spandrels” paper of 1979).
Gradualism in particular, with the concomitant implication that natural selection and adaptation account at least in large part for the history of life on earth, became in post-modern synthesis times a commitment to what is claimed by its critics to be a simplistic micro-mutationism, a denial of the need for big, morphology-altering steps – for monsters. Two heroes, first among few equals of Blumberg’s exposition, are William Bateson (1881-1926), geneticist, an early follower of Mendel, who stressed, however, the necessity for discontinuous (and large!) changes from one generation to the next (mutations), and Richard Goldschmidt (1878-1958), embryologist and evolutionist, who likewise insisted that the raw material of evolutionary change must be significant jumps (saltations) of body-plan, brought about by mutations of large effect, arising spontaneously in the course of development. The argument, in short, was that macro-mutations are needed for macro-evolution – the change of one body plan into another.
To take the reader down the path of this argument, updated and rationalized, the author presents with enthusiasm, documentation, and fascinating details what he describes, justifiably, as “a parliament” of monsters. The story of an eight-limbed Indian baby girl vies with that of conjoined twins of various kinds, human and otherwise; with “parasitic” human twins; with two-headed animals; and with quadrupeds born with two, rather than the requisite four, legs; and in all these interesting cases with the surprising functionality that can and does emerge in the recipients of these large developmental variations.
These, the argument goes, tell us that significant, non-lethal departure from developmental norms is not just mutation in a gene; noteworthy plasticity of form and function is inherent in the fundamentals of developmental mechanism. Development is a system of densely reticulated chemical and physical processes that control a morphogenesis that is implied, but by no means blueprinted in any simple way, in the genome. Development, in short, is the complex outcome of very large numbers of processes, only some of which are genetic. Others are epigenetic, including environmental. And among the multitude of such outcomes in any species population, there will be differences, variations, some of them large enough to affect the body plan.
To be sure, then, Darwin’s sine qua non for evolution was natural biological variation; but too soon, following the rediscovery of Mendel’s work, the variations upon which Darwinism came to be built was understood as ordinary gene (micro-) mutation. What was needed was the recognition of developmental mechanisms, rather than elementary genetic change, as the substrate of evolution, and the channeling (constraints) imposed on developmental outcomes by those mechanisms. Such constraints are, in the most aggressive versions of evo-devo, the real material of evolutionary change.
The author’s argument along these lines can be encapsulated in several possible quotations from the book. Here is one, having to do with the (quite well understood) mechanism of sex-determination, “normal” and aberrant (?):
In general, most of us think of these effects as downstream from the ultimate source of sex determination – the sex chromosomes. Indeed, in most species, sex chromosomes do help to determine whether an ovotestis develops into an ovary or other factors also come into play to advance, and sometimes deviate, the sex-determining process. (p. 226)
But he goes on, then, to discuss sex-determination in crocodiles, turtles, and fish, in which he observes that sex-determination “is hardly ‘written in the genes’ because they simply do not have the sex genes to be written on.” (Sex in these animals is determined by temperature.) So to advance the argument a notch: genes don’t explain everything about adult form and function.
Does anyone argue with this? No serious developmental geneticist among those I know does. More to the point: are the well-known epigenetic inputs to morphogenesis ignored or denied by evolutionary biologists? By “Darwinians”? No. Not in any obvious way at least. I am myself a developmental biologist, and the fact that it is development that natural selection operates upon has been a given among my students and collaborators for more than forty years. The key question for evaluation of the argument of this fascinating book (and recently others like it) is, rather, the other claim: that variations, mutations of large effect, freaks – and not micro-mutations – are the raw material of “macroevolution.”
That claim is unproven. The original argument against these (“hopeful monsters,” as the often-luminous Goldschmidt described them) is that unless they are either at an immediate advantage over their “normal” siblings in the common environment, or just as successful in reproduction as their siblings in that environment, they will be eliminated by negative selection. And while neutrality of effect can be very common at the level of genes, so far as we can tell it must be very rare at the level of monstrosity.
Paul R. Gross is University Professor of Life Sciences Emeritus at the University of Virginia and the coauthor, with Barbara Forrest, of Creationism’s Trojan Horse (rev ed, New York: Oxford University Press, 2007).