Jean Guex. Retrograde Evolution During Major Extinction Crises (SpringerBriefs in Evolutionary Biology). New York: Springer, 2016. 77 pp. $54.99 USD (Paperback ISBN: 9783319279169).
Jean Guex is Professor Emeritus at the University of Lausanne. This book provides an in-depth analysis of the retrograde evolution occurring during major extinction periods. The text offers a non-strictly adaptive explanation of repetition of phyla after the major extinctions, studying seven phylogenetically distinct groups. It notes that the path of evolution was turbulent, and often the genesis of new species was interrupted by mass extinctions. The responses of life to these disruptions are the theme of this book. These mass extinctions are associated with global catastrophes that suddenly presented living things with severe stress by narrowing the conditions for survival. These mass extinctions triggered what Guex has consistently called “retrograde evolution.” In short, the mass extinction events and the stress they caused instigated the emergence of ancestral forms of many organisms, forms that were apparently extinct for many millions of years. This opens up a new experimental field of reconstructing ancestral forms in evolutionary biology in the lab by applying artificial stresses.
Most of the evolutionary trends discussed within this text concern more or less gradual geometrical and ornamental transformations occurring over long periods of ecologically stable periods. Chapter 1, “Evolutionary Trends During Periods of Relative Ecological Equilibrium,” covers these trends more fully. He notes in this frst chapter that paleontologists generally use the term “evolutionary trend” to describe the oriented morphological transformations occurring in stratigraphic sequences of one particular species or in phyletic series of closely related species. In some cases, these trends are gradual and are used as a biochronological clock for stratigraphic correlations. In most cases, however, these trends appear as discrete sequences of closely related species belonging to a single lineage showing an oriented morphological variation. By contrast, most major evolutionary jumps – at least within invertebrate groups – occur during massive extinction periods, which are characterized by the appearance of primitive forms resembling remote ancestors of their immediate progenitors, forms of which are called atavistic. Chapter 2 addresses how homeomorphic species generated during sublethal environmental stress can be separated from the ancestral group by several millions of years. The concept of sublethal environmental stress denotes specific conditions that are critical to the survival or normal development of living organisms. Most of the manifold studies of sublethal environmental stress that occurred during major extinction events which are studied by paleontology are devoted to a census of the biodiversity variations rather than to the understanding of the basic phenotypic and epigenetic variations induced by environmental perturbations. The modes of evolution during mass extinction events, the characteristics of organism surviving the crises, and what types of transformations have affected them have not been explored to a significant extent. Guex seeks to rectify this glaring omission.
In chapter 3, Guex presents a new theoretical model of retrograde evolutionary changes during sublethal environmental stress and analyze the evolutionary patterns of some planktonic foraminifera, and within chapter 4 he does the same with respect to reversals in radiolaria. Indeed, in the third chapter discusses Ticinella-Thalmanninella, which is a recently fundamental example of an identified lineage that starts from a very primitive form, and thereafter gives rise to more complex forms with an involute and carinated shell. Guex presents this discovery in this chapter. Chapter 4 notes that radiolarians, since their first appearance in the Cambrian period, have experienced several near extinctions, but have amazingly survived well until the present time. In this chapter, it is demonstrated that following the Permian extinction, some forms reduced the complexity of their skeleton by partial loss of the outer spherical shell that surrounds the spicule. Chapter 5 then segues to evolution of some cephalopods during major extinctions. This chapter notes the process of iterative evolution, which is the most striking property of ammonoid distribution during their long life. Three groups of very large scale groups are presented to show that they are characterized by rapid appearance of simple, primitive-looking forms that are similar to remote ancestors of their more complex immediate progenitors.
The sixth chapter presents the retrograde evolution of corals at the end Triassic crisis. During the Permian-Triassic crisis, corals were obliterated, and the Triassic recovery of corals with hexagonal radiate structure took several millions of years. Chapter 7 discusses the retrograde evolution of early Triassic conodonts. Conodonts were eel-shaped jawless animals, which are possibly related to the modern cyclostome. They proliferated during the Paleozoic and Triassic periods, and disappeared during the end Triassic extinction event. Since they generally well preserved, they are studied extensively as biostratigraphic markers. Chapter 8 discusses genetic memory in the evolution of silicoflagellids. Atavisms appearing during massive extinctions or sublethal environmental stresses indicate that retrograde evolution is related to some genetic memory of the phylogenetical history of the group, which is reminiscent of Haeckel’s recapitulation theory. This fact suggests that biological experiments could be performed to reconstruct partial phylogenies of recent animals or plants by submitting them to sublethal artificial stress. The ninth chapter is composed of the volume’s conclusions. The volume also contains an extensive collection of references, and is finished off with a comprehensive index.
In sum, Guex herein presents a novel theory known as retrograde evolution. It has wide-reaching implications for the reconstruction of both animal and plant phylogenies. I could see this text being use as supplementary text within introductory biology classes at the undergraduate level. For such a purpose, I recommend this title.
Bradford McCall, Holy Apostles College and Seminary