Keywords

Life

Richard Benedict Goldschmidt was born in an upper middle-class Jewish family on April 12, 1878, in Frankfurt-am-Main, Germany. His relatives included bankers, professors, lawyers, and businessmen, and his father was a wealthy merchant, running a successful confectionery shop. Goldschmidt studied Latin, French, and mathematics for 9 years, Greek for 6 years, and natural history for 3 years at the local gymnasium. Goldschmidt’s parents wanted him to become a doctor, so he entered the University of Heidelberg in 1896 as a medical student. He took foundation courses in medicine from the anatomist Karl Gegenbaur (1826–1903) and the zoologist Otto Bütschli (1848–1920), whom Goldschmidt admired very much and was the reason he had chosen the University of Heidelberg. Two years later, Goldschmidt passed the premed exam, but he did not want to be a doctor anymore, so he transferred to the University of Munich to study zoology in the lab of the famous zoologist Richard Hertwig (1850–1937) at the Zoological Institute at the University of Munich. A former student of Goldschmidt’s at Hertwig’s lab, Karl von Frisch (1886–1982), a Nobel Prize winner in physiology, was amazed by the amount of work that Goldschmidt produced and his efficiency (Frisch 1980). In Hertwig’s lab, he started to conduct experiments related to the morphology of Ascaris and Amphioxus. In 1899, he returned to the University of Heidelberg to study in Otto Bütschli’s lab, and in 1900, he published his first scientific paper on the development of the tapeworm Echinococcus (Goldschmidt 1900). Goldschmidt finished his doctoral dissertation entitled “Fertilization and Early Development of the Trematode Polystomum” in 1902. After graduation, Goldschmidt served his compulsive time in the German army for a year.

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Richard Goldschmidt’s portrait. (Reprinted by permission from Springer Nature: Nature Reviews Genetics, Richard Goldschmidt: hopeful monsters and other “heresies,” Michael R. Dietrich, Copyright 2003)

In 1903, Goldschmidt returned to Hertwig’s lab at the University of Munich, working as an assistant to oversee the experimental courses, remaining there until 1914. His students at the time included Hans Nachtsheim (1890–1979) and Jakob Seiler (1886–1970), who later became prominent zoological geneticists in Germany. A year later, he married Else Kuhnlein with whom he had two children, Ruth and Hans, born in 1907 and 1908, respectively.

In 1909, Goldschmidt became a lecturer (Privatdozent) at the University of Munich. Later, he started his genetic experiments with two kinds of moths, the nun moth and the Gypsy moth, Lymantria dispar, which he would study for decades afterwards. Goldschmidt took a Mendelian approach and conducted cross experiments on the Gypsy moth to study a sex determination pattern, which received much attention. In 1911 he published a book entitled Einführung in die Vererbungswissenschaft (Introduction to Genetics) and became a proponent of the emerging field of genetics in Germany.

In 1914 Goldschmidt was appointed director of the Animal Genetics Department of the newly founded Kaiser Wilhelm Institute for Biology in Berlin-Dahlem. This position did not require him to teach, so he was free to focus on research. While the buildings of Kaiser Wilhelm Institute were under construction, on January 4, 1914, he headed to Japan to collect Asian species of the Gypsy moth through the Albert Kahn Travelling Fellowships, which were awarded to scholars in Germany, France, Britain, Japan, and the USA to promote cultural understanding (Richmond 2015). He used these Asian specimens to cross them with European species to study their sex determination and evolution. Goldschmidt enjoyed traveling around the world for the rest of his life, visiting places such as Korea, China, Russia, and Polynesia because of his interest in Oriental art and collecting art objects.

Because of the outbreak of the First World War, Goldschmidt was not able to return to Germany from Japan because of the embargo on German ships, and in 1914 he had to go to the USA. He first disembarked in California and stayed at the Zoology Department of the University of California, Berkeley. Believing that he might find a way back home more easily on the East Coast, he headed to New York. However, he was unsuccessful and struck in the USA longer than he expected. He was accepted as a visiting professor in Ross Harrison’s lab at Yale, and his family later joined him. Because he worked on Lymantria, a pest species restricted by the USDA, he had to move to Harvard’s Bussey Institution at Woods Hole to breed his moths. However, when the USA entered the war in May 1918, he was sent to an internment camp because of the anti-German sentiment. Eight months later, he was released and returned to Germany, where he resumed his old post in the Kaiser Wilhelm Institute for Biology in Berlin-Dahlem.

As a physiological geneticist, Goldschmidt investigated the problem of how genetic material controlled development. He published a small book consisting of a few essays on his work on Lymantria dispar in 1920 and a summary of other embryologists’ research on the link between genetics and development. During the 1920s, Goldschmidt taught at the Imperial Tokyo University for 2 years and developed good relationships with Japanese scientists. Goldschmidt published Lymantria in 1933 in which he synthesized his work on sex determination and geographical variation in the Gypsy moth. Both books were well received, both in Germany and abroad, and established his solid status as a prominent geneticist. Due to the purge of Jews in Germany, Goldschmidt was forced to resign, and, once again, he migrated to the USA in 1935. At that time, he was one of the most prominent geneticists in Germany, but not in the USA. Moving to the USA for refuge was a hard transition for him because he had to adapt to a different language, culture, and academic atmosphere. In 1936, he managed to secure a professorship at the University of California in Berkeley, but this new position required him to take on teaching obligations. For his first year in the USA, he was a lecturer for a large lower-level course in animal biology for 500 students, and only later he started teaching higher-level courses. From 1939 to 1940, he gave the famous Silliman Memorial Lectures on evolution at Yale University. In 1940 he published The Material Basis of Evolution, which was not received well by its critics, especially the neo-Darwinian scholars, who were attempting to forge a unified theory of evolution and interpreted Goldschmidt’s theory as disrupting their consensus. Goldschmidt was viewed as an iconoclast for his evolutionary theory, although he was able to popularize the distinction between macroevolution and microevolution. Goldschmidt was elected a fellow of the National Academy of Sciences in 1947.

After Goldschmidt retired from UC Berkeley in 1948, he continued to publish a stream of theoretical papers to defend himself against neo-Darwinians. He delivered the Presidential address to the 9th International Congress of Genetics in Bellagio, Italy, in 1953. In contrast with the experimental and statistical characteristics of genetics at the time, Goldschmidt published Theoretical Genetics in 1955, in which he summarizes his experience in issues such as the nature of the genetic material and how the genetic material controls development (Goldschmidt 1955). Goldschmidt died on April 24, 1958, after a heart attack, in Berkeley.

Work

Sex Determination of the Gypsy Moth

When Goldschmidt first joined Hertwig’s lab in 1898, he was exposed to the problem of sex determination, the main focus of the lab, but more from a morphological perspective. After the rediscovery of Mendel’s work, scientists, including Hertwig’s lab members, participated in a race on conducting Mendelian cross experiments where if one knew the alleles of the parental generation, one could predict the ratio of the phenotypes of the offspring generation by calculating the combination of alleles. However, when Goldschmidt crossed the Gypsy moth to observe the sex determination pattern, he was not able to use the Mendelian theory to explain his results, and this observation raised his skepticism about the Mendelian genes. He did not accept particulate “genes” as determiners of characters but had a developmental notion of genetics in which factors acted quantitatively (similar to enzymes) in development to determine characters.

When conducting cross experiments on the European species and Japanese species of the Gypsy moth, Goldschmidt observed that not all moths displayed definitive sexuality. Instead, some displayed both female and male traits. He used the terms “intersexes” and “intergrades” to refer to those moths that displayed traits of the opposite sex in different developmental stages. For example, an intersex moth might first display male traits and, later in development, experience sex reversal by developing female traits. Goldschmidt observed that nongenetic factors could also influence sex determination, and by manipulating the temperature and other environmental factors, he was able to produce intersexes in an orderly way. Goldschmidt concluded that the sex of the moth was not a qualitative trait but rather a quantitative one because, first, a moth could show both female and male characters and, second, the sex of the moth was determined by the quantity of female and male determiners.

To account for the production of intersexes, Goldschmidt proposed what he referred to as “the balance theory of sex determination” (Goldschmidt 1923). He used the word “determiner” instead of “chromosome” or “gene” to name the hereditary material that determined sex. He departed from Mendelian genetics in arguing that sexuality in the Gypsy moth was determined by one female determiner (denoted as F) and one or two male determiners (M or MM). He further argued that the determiner controlling sexuality was quantitative and that some determiners were weaker and some determiners were stronger. Through development, the male determiner(s) and the female determiner had different strengths and competed with each other. For example, if an offspring had a strong F and a weak M (FsMw), it would be a female; however, if it had a weak F and two strong Ms. (FwMsMs), it would be a male. However, if it had a strong F and two weak Ms. (FsMwMw), it could be an intersex female and would experience sex reversal. Using this theory, Goldschmidt was able to produce the intersexes in the rate he predicted.

To link his balanced theory of intersexuality with physiological and developmental processes, Goldschmidt proposed what he called “the time law of intersexuality” (Goldschmidt 1923). Goldschmidt treated the sex determiner as a gene for the simplicity of analysis, but he thought that, in reality, sex determination involved many genes that controlled different developmental processes. He used a graph to explain the time law, in which he plotted the strength of the male and female determiners as two intersecting curves. For intersexes, when the strength of female determiners was higher than that of the male determiners, the intersexes were female and vice versa. The intersecting point of the two curves was the turning point, which explained the sex reversal point of the intersexes. Goldschmidt’s critics received his balance theory better than the time law, criticizing the latter for its theoretical nature. Therefore, during the 1930s, the time law became mostly obsolete.

Physiological Genetics

Goldschmidt summarized and generalized almost two decades of his work on the Gypsy moth, as well as other scientists’ investigations of how genes controlled development in his 1927 book, Physiologische Theorie der Verebung (Physiological Genetics), which was translated into English in 1938 (Goldschmidt 1927). Goldschmidt investigated variation, heredity, physiology, development, and evolution all in this one book and argued the importance of bringing development and physiology back to genetics. In fact, according to many nineteenth century biologists’ theories, such as August Weismann (1834–1914) and Hugo de Vries (1848–1935), heredity, development, and evolution were inseparable phenomena (Allen 1974). However, following the Mendelian and Morgan school, heredity could be approached without considering either development or evolution. While this approach had proved to be experimentally successful, Goldschmidt argued that understanding the transmission of genes was only one side of understanding heredity. The other side was “to understand how the gene, whatever it is, acts in controlling typical development to the adult form showing all the hereditary traits” (Goldschmidt 1938, p. 1).

Central to Goldschmidt’s theory was the concept of rate, as he argued that genes determined traits by changing the rate of development, because the function of mutations was changing the rate of the developmental processes and the time of the onset of genes. He argued that genes acted like an “autocatalyst” to regulate developmental processes, as opposed to the predominant notion of transmission genetics, championed by the Morgan School, which proposed that genes, like beads-on-a-string, were discrete particles. Goldschmidt attacked this corpuscular notion of the gene and claimed that genes were not corpuscles in a linear sequence, but, instead, they had a hierarchical organization (Goldschmidt 1938; Dietrich 2003). He publicly announced that “the theory of the gene is dead” and predicted that in a few decades, scientists would no longer use the word “gene” (Allen 1974).

Goldschmidt’s Physiological Genetics was not received well by the Morgan School, including Alfred Henry Sturtevant (1891–1970), Calvin Bridges (1889–1938), and Thomas Hunt Morgan (1866–1945), although the book referenced many of its members. Some of the disagreements referred to empirical issues. For example, Morgan did not accept Goldschmidt’s notion of genes as enzymes (Morgan 1926). But, as argued by Marsha Richmond, there were “fundamental philosophical differences” between the views of the Morgan School and those of Goldschmidt in that Morgan held a corpuscular notion of genes and Goldschmidt insisted on the quantitative notion of genes (Richmond 2007). Although Goldschmidt did not indicate what exactly the gene was and in some of his writings he described it as similar to an autocatalyst or an enzyme, he clearly pointed out that genes were not linearly arranged particles in chromosomes as treated by the Morgan School. Instead, Goldschmidt believed that “the gene has not necessarily a definite limitation” (Allen 1974, p. 49). It is precisely because he believed that heredity and evolution could only be understood by studying the physiological and developmental processes involved, that he held a quantitative and dynamic rather than a qualitative and static view of the gene. This quantitative and dynamic approach attempted to “understand general phenomena in terms of genic action and developmental systems with all their consequences of interaction, embryonic regulation, and integration” (Goldschmidt 1954, p. 703).

Goldschmidt’s work was better received in the UK (Richmond 2007), probably because many British biologists had introduced similar concepts as those of Goldschmidt’s. For example, the idea that the speed of developmental processes can influence the phenotype was similar to the notions of “rate genes” and “allometric growth” used by Julian Huxley (1887–1975) and the “heterochrony” concept used by Gavin de Beer (1899–1972). As embryologists, they all realized the importance of incorporating development in evolution. For example, Huxley, who met Goldschmidt in 1916 at Woods Hole and remained in contact with him until 1955, was receptive of Goldschmidt’s approach of combining evolution, development, and genetics, and he viewed Goldschmidt’s physiological genetics as almost as important as the transmission genetics advocated by the Morgan School (Huxley 1942; Richmond 2007). Huxley was very familiar with all the writings of Goldschmidt and cited his research on the Gypsy moth extensively in his 1940 book, Evolution: The Modern Synthesis (Huxley 1942).

Microevolution and Macroevolution

The most contentious aspect of Goldschmidt’s research concerned evolution, especially with regard to speciation. As early as in 1933, in a meeting of the American Association for the Advancement of Science held in Chicago, Goldschmidt presented his insights on evolution (Goldschmidt 1933b). He argued that an often-neglected issue in the theory of evolution was understanding the nature of the developmental system of the organism which underwent evolutionary change (Goldschmidt 1933b). Goldschmidt never questioned evolution itself as a fact. Rather, what he had skepticism about was how evolution changed the genetic material. He believed that simply changing individual genes could not result in species change; rather, macroevolutionary change must be based on other processes.

A hotly debated topic among population geneticists then was whether geographical isolation was the starting point of speciation. Goldschmidt opposed this view and endorsed the concept of “preadaptation” to refer to those mutations that had no adaptive value in the original environment but became adaptive when introduced into a new environment. Goldschmidt argued that geographical isolation was not a starting point but a means that allowed preadaptive traits to become adaptive. Through his study of the Gypsy moth, he concluded that subspecies did not become separate species because of geographic isolation; they just adapted to different areas, and their differences were in degree not in quality. Instead, he maintained that new species formed in the same area along with old species, and profound developmental changes happened not gradually but suddenly (Goldschmidt 1933a). Therefore, he denied the existence of incipient species.

His research on how genetic material evolved culminated in the publication of The Material Basis of Evolution (1940). The book had two parts: one on microevolution, the evolution within a species based on accumulative small mutations, and the other one on macroevolution, the evolution at or above the level of species. Neo-Darwinians usually assumed that only small accumulative variations, or microevolution, led to speciation. In contrast, Goldschmidt argued that microevolution only explains evolution after a species is formed, like geographic variations which allows subspecies to adapt to different niches, but that there is a “bridgeless gap” between species, and that big changes must occur rather rapidly to bridge that gap. Goldschmidt used the term macromutation to describe a mutation that has a large phenotypic effect in contrast with micromutation, which refers to a mutation that involve only one single gene locus. Macroevolutions resulted in profound changes in genetic systems, and thus the development systems, which he also referred to as reaction systems.

To explain how these changes happened, Goldschmidt proposed two types of macromutations, since they are the material basis of evolution. The first was “developmental mutation,” which referred to the macromutation that happens in a developmentally important locus or in early embryonic processes. To find empirical evidence for macromutations, Goldschmidt studied the problem of homeosis, or the transformation of one organ into another organ, in Drosophila in the 1940s and 1950s (Dietrich 2000). For example, he studied a homeotic mutant podoptera, which can transform wings into leglike structures, and tetraltera, which can transform wings into halteres, a pair of dumbbell-shaped organs for keeping balance. The second type of macromutation was “chromosomal mutation” or “systematic mutation,” which referred to large-scale systematic rearrangement of chromosomes as a mechanism of speciation. His proposition of chromosomal mutation is derived from Morgan’s study of the linkages of alleles, the doubling of the chromosomes in plants, as well as Hermann Joseph Muller (1890–1967)‘s study of the effects of X-ray radiation and Alfred Sturtevant (1891–1970)‘s discovery of the position effect. He argued that several successive repatterning of the chromosomes needed to reach a threshold for a systematic mutation to happen (Goldschmidt 1940).

In Goldschmidt’s view, the result of macromutations was mostly lethal to the organism, which he called “monsters,” but in very rare circumstances, it was able to produce a new species with large changes, which he dubbed “hopeful monsters.” Although homeosis served as evidence for “developmental mutations,” he lacked both empirical evidence and genetic evidence of “systematic mutations.” Thus, his theory was in a disadvantageous position compared with the neo-Darwinian approach to evolution that was being established by several scholars at that time. However, Goldschmidt argued that the lack of direct empirical evidence on macroevolution was not a problem to his theory: “It would be very cheap criticism, indeed, to say that nobody has ever witnessed a process. Neither has anyone witnessed the production of a new specimen of a higher taxonomic category by selection of micromutations” (Goldschmidt 1952, p. 97).

Legacy

For some biologists, Goldschmidt’s greatest contributions lie in his work on sex determination in Lymantria and his contributions to physiological genetics (Caspari 1980). Although the term “gene” has not disappeared from scientific practice as preconized by Goldschmidt, in philosophy of biology, the nature of the gene has been hotly debated, and Goldschmidt’s account has some merit in today’s view of the gene. The discovery of introns, exons, and alternative splicing of genes suggests that gene expression is regulated by many factors, indicating that genes are not corpuscular but rather quantitative, as Goldschmidt thought (Griffiths and Karola 2006). Goldschmidt delved into a variety of experiments, but the most notable one was his study on the nervous system of nematodes. This work did not bear much fruit in Goldschmidt’s life but influenced Sidney Brenner, who was awarded the Nobel Prize in 2002 for his work on the neural development of nematodes (Ankeny 2001).

According to Stephen Jay Gould (1941–2002), Goldschmidt was not received as a serious figure in evolutionary biology by his contemporaries despite Goldschmidt’s prominence as a geneticist. In Gould’s words, it almost became fashionable to ridicule Goldschmidt’s work (Gould 1982). Some historians suggest that Goldschmidt was not afraid of creating controversy because he wanted to get attention in the USA (Dietrich 2011). When The Material Basis of Evolution was published, it met objections from some prominent neo-Darwinians who were forging the new evolutionary synthesis, and Goldschmidt threatened the unification of evolutionary biology. Goldschmidt jokingly said that he “had struck a hornet’s nest” (Goldschmidt 1960, p. 324).

Mayr’s book, Systematics and the Origin of Species (1942), referenced Goldschmidt many times, and the book shows that Mayr was very familiar with Goldschmidt’s work on sex determination of the Gypsy moth and opposed him fiercely, although personally the two were friends. The fundamental difference between the two was that Mayr held that geographical isolation was a necessary condition for speciation, while Goldschmidt believed that chromosomal differences could also induce sexual isolation that leads to the formation of a new species, and geographical isolation was not necessary. Mayr criticized Goldschmidt for basing his notion of speciation largely on the data from Lymantria. In addition, Mayr criticized Goldschmidt for his lack of population thinking, arguing that the “hopeful monster,” even when produced, could not survive in a population (Mayr 1997, p. 32).

Theodosius Dobzhansky (1900–1975) had heard Goldschmidt’s Silliman Lectures and referenced Goldschmidt dozens of times in his own book Genetics and the Origin of Species. Dobzhansky wrote a review of The Material Basis of Evolution in which he argued that Goldschmidt’s theory fell into catastrophism and criticized it for it rejecting evolution (Dobzhansky 1940). He thought that Goldschmidt’s understanding of genetics was different from that of most other geneticists, and he referred to the “hopeful monster” metaphor as just “a belief in miracles.” Goldschmidt defended himself, saying that he was not against evolution as suggested by Dobzhansky but instead embraced the major tenets of Darwinian theory (Goldschmidt 1952).

Similarly, compared with Goldschmidt’s physiological genetics, Huxley was less receptive of his evolutionary theory. A firm defender of gradualism, Huxley thought that it was hard to draw a definitive line between species or subspecies, so he did not believe in “bridgeless gaps.” George G. Simpson (1902–1984) believed that homeosis, as an example for macromutation, differed from micromutation only in degree, and a few such mutations were not enough to create a new species. It might require the accumulation of many homeotic mutants for speciation. Moreover, Goldschmidt needed to explain how macromutation affected a population instead of an organism (Simpson 1944).

Other evolutionary biologists received Goldschmidt’s ideas more favorably. Conrad H. Waddington (1905–1975) remarked that “Goldschmidt’s book is one of the most important recent contributions to the theory of evolution” because Waddington himself criticized neo-Darwinians for reducing the evolution of phenotypes to the evolution of discrete units of genes (Waddington 1941). Another example was Sewall Wright (1889–1988), one of the founders of the modern synthesis. In his review of The Material Basis of Evolution, Wright agreed with the existence of “developmental mutations” by pointing out that a single mutation could give rise to repetitive homologous structures (Wright 1941). Although a gradualist, who assumes that evolution results from slow and accumulative processes, Wright acknowledged that evolution could take place at different speeds. However, he rejected systematic mutations by arguing that chromosome rearrangement was mostly detrimental, and, if not lethal, it would have less of an effect than a single mutation or no effect at all. He also thought the hypothesis of “bridgeless gaps” between species was a too radical claim.

Although Goldschmidt’s contribution was often looked down upon by many of his peers, Goldschmidt himself was optimistic about his work and expected it to be rediscovered by others in the future, just like Mendel’s work had been. In his autobiography, published posthumously in 1960, he remarked that “I am confident that in 20 years my book, which is now ignored, will be given an honorable place in the history of evolutionary thought” (Goldschmidt 1960).

In terms of Goldschmidt’s contributions to neo-Darwinism perceived after the 1980s, there are differing views. Although Ernst Mayr (1904–2005) claimed that Goldschmidt’s ideas actually failed to influence major neo-Darwinians (Mayr 1997, p. 31), the historian Michael Dietrich has argued instead that Goldschmidt’s heresy “helped define the neo-Darwinian orthodoxy” (Dietrich 1995). Similarly, Manfred Laubichler has argued that Goldschmidt was an important figure in the modern synthesis because he provided a target for neo-Darwinians and spurred many scientific debates (Laubichler 2009).

As Goldschmidt indeed predicted, his work was revived by Gould in the 1980s (Dietrich 1995). Gould learned about Goldschmidt’s theory of macroevolution and speciation while taking Mayr’s classes as a graduate student (Dietrich 1995). Gould declared that he had sympathy for Goldschmidt because the latter was ridiculed by people who had not read his work, and thus when The Material Basis of Evolution was republished in 1982, Gould wrote the Preface (Gould 1982). According to Dietrich, The Material Basis of Evolution has received more citations after the 1980s than at the time when Goldschmidt was still alive (Dietrich 2011).

Gould’s theory of punctuated equilibrium assumed that species stayed in a relatively stable status with few genetic changes for a long time, and then significant changes happened rapidly; thus one species could split into two. This theory supports saltation, which assumes that evolution happens through sudden changes, instead of gradualism. Gould also opposed the neo-Darwinian view that the gradual accumulation of small variations could account for all of evolution. He was receptive of Goldschmidt’s developmental mutations and yet critical of his systematic mutations; he defended Goldschmidt, maintaining that he did not represent the opposite of Darwinism as neo-Darwinians tried to argue by pointing out that Goldschmidt acknowledged the importance of small genetic changes as well (Gould 1977).

Dietrich has argued that after Gould revisited Goldschmidt’s work on evolution, Goldschmidt was viewed widely as a heretic by many historians and scientists, including himself (Dietrich 2011, 2003). Goldschmidt popularized the distinction between microevolution and macroevolution, and his argument fell into the larger debate between saltationists and gradualists. This debate ended with the dominance of the neo-Darwinian scholars supporting gradualism while Goldschmidt was still alive. However, the debate between saltation and gradualism and between microevolution and macroevolution has continued, through scholars like Gould revisiting Goldschmidt. For example, some evolutionary biologists proposed the concept of “neo-Goldschmidtian saltation” and argue for gradualism in the evolution of genetic sequence and punctuated equilibrium in morphology (Bateman and DiMichele 2002).

Goldschmidt’s contributions to evolutionary theory have received more attention after the emergence of evo-devo, not just because of Gould but also because of advancements in developmental genetics. Laubichler has argued that, ironically, although development is often overlooked in the modern synthesis, developmental genetics has provided new results regarding the origin of variations (Laubichler 2009). The discovery of Hox genes in 1978, which are the genes underlying homeosis, is an example of changes in a few loci that could make big phenotypic alterations (Lewis 1978). To many, evo-devo began with the discovery of Hox genes and, therefore, since the 1980s, modern biologists and historians have frequently revisited Goldschmidt’s theory about macroevolution and hopeful monsters (Hall 2003).

Some biologists are even more hopeful about the “hopeful monsters.” Günter Theißen argues that they can be useful in explaining the origin of innovations that cannot be explained by gradual evolutionary processes. He describes some scientific evidence of quantitative trait loci analyses that show that a few genes can have large effect, among which the most prominent example are the Hox genes (Theißen 2006). Olivier Rieppel argues that turtles might be descendants of surviving hopeful monsters because turtles have a very unusual shell structure that does not resemble any of their phylogenetic relatives. The innovation of turtle shell might be due to a macromutation instead of gradual evolution (Rieppel 2001). Eva Jablonka and Marion J. Lamb endorse hopeful monsters from a different perspective, maintaining that environmental changes might produce epigenetic inheritance that affects many genes, giving rise to novelties. They argue that environmental factors can produce epigenetic changes at a population level and dismiss the problem of “lonely” hopeful monsters (Jablonka and Lamb 1999, p. 224).

Cross-References