Every year at the beginning of February there is a Gem Show in Tucson. I always go to the Tucson House Hotel on St. Mary’s Rd. to see the fossil exhibits. Across one wall is an offering of books from the Black Hills Institute (2). There are adult and children’s books on fossil collection and fossils but also a wonderful collection of books on evolution. Over the years, I’ve picked up many great books. This is one of them.
Dr. Rieppel’s book is about the origin of turtles and the controversies of turtle origin that apply to the history of evolutionary thought. Some cladistics research places turtles with pre-reptiles while others place them with dinosaurs, birds, and crocodiles, while the DNA evidence places them with crocodiles only. The term “Hopeful Monsters” comes from Richard Goldschmidt’s critique on genetics. Although Goldschmidt’s theories are not accepted today, many people studying embryo development or studying the fossil record still accept his critique. The problem with turtles is that the turtle body plan is unique in reptiles and there is no way to relate it to systematic transitional forms. This goes against the Neo-Darwinist dogma of gradual evolution. The argument is not that the fossil record is incomplete but that there may be evolutionary changes that can happen quickly and dramatically. This idea has been called saltation, macroevolution, and to some extent, punctuated equilibrium. This book is not: ”Darwin is wrong.” A silly idea that book publishers like to put on covers to sell more books. Stephen Jay Gould in The Structure of Evolutionary Theory (4) likens Neo-Darwinism to a three-legged stool, the theory supported by the three foundations of variation, natural selection, and genetic inheritance. The purpose of any critique is not to undermine or replace this support but to enrich the theory by explaining phenomena that do not quite fit. Transitional forms show up all the time, horses’ toes turning into hooves, whales from land-dwelling creatures with legs to water dwelling with fins. Feathers on dinosaurs are used for insulation and sexual display to flight in birds. In all these examples, the fossil record provides transitional forms. Evolution happens at all levels of time but the big question is: Does it happen the same way? I am reminded of Mary Jane West-Eberhard’s comment (3) that natural selection acts on traits, not individual genes. The trait here in question is the carapace, the turtle’s upper shell. Changes here are not only to the dermal outer layer but to the skeleton itself. Developmental pathways may contain thousands of genes as well as regulatory regions that are genomic but not necessarily genetic. Goldschmidt called these “Hopeful Monsters,” large successful major changes that have survived Natural Selection. These changes are by necessity rare but still a possible way that Evolution might work.
Rieppel places his book in the historic framework of evolutionary thought including much I haven’t seen about German zoology including the unfortunate tendency of some to follow and support Nazi racist thought. Goldschmidt himself was a refugee from the Nazi purges of “Jewish science.” Rieppel concludes with the finding of a primitive fossil turtle in China in 2016. This turtle represents the oldest known turtle and looks very much like an embryonic form. It is still very much a turtle so the mystery is still: Are turtles Hopeful Monsters?
1. Rieppel Olivier. Turtles as Hopeful Monsters: Origins and Evolution (Life of the Past), Indiana University Press, 2017.
2. “Black Hills Institute of Geological Research.” Accessed February 26, 2020. https://www.bhigr.com/.
3. West-Eberhard, Mary Jane. Developmental Plasticity and Evolution. Oxford University Press, 2003.
4. Gould, Stephen Jay. The Structure of Evolutionary Theory, Harvard University Press, 2002.
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