User:Ragesoss/Embryo drawings

Introduction
Embryo drawings refers to any representation of the illustration of embryos in a developmental sequence. In sexually reproducing organisms, an embryo develops from a zygote. The zygote, a cell produced once the sperm fertilizes the egg cell, divides by mitosis into a multicellular organism. This multicellular organism is referred to as the early developing embryo. Embryo drawings are particularly important in establishing a means of comparison between embryos of different classes in order to further influence the fields of biology and embryology. Such embryo drawings, pioneered by Ernst Haeckel, have caused much controversy over the past century regarding the originality and exactness of such drawings that have so strongly influenced modern scientific research. It has been determined over the past century that although early embryos do exhibit certain similarities, Haeckel seems to have exaggerated the similarities and de-emphasized the differences in order to promote his theory of evolution from common descent and his theory of recapitulation.

Numerous critics throughout the late eighteenth and early nineteenth centuries, specifically Karl von Baer and Wilhelm His, established embryo drawings of their own that strongly contradicted Haeckel’s theories, noting the distinct differences in early embryological development through empirical observation. Both His and von Baer note the misconceptions in Haeckel's theory of recapitulation, as Haeckel argues, "ontogeny is the short and rapid recapitulation of phylogeny." . Rather, His and von Baer believe that living embryos do not reproduce and re-experience the evolutionary process that their pseudo-ancestors underwent, arguing that embryos do not follow the path of development from a fish to a reptile, and ultimately through to a human.

Opposition to Haeckel's fraudulent embryo drawings has recently emerged in the late twentieth and early twenty-first centuries as well. Haeckel’s contemporaries, such as Jonathan Wells, Michael Richardson and Stephen Jay Gould, recognize the forgeries in Haeckel’s embryo drawings. In addition to omitting and adding certain features to his drawings to exhibit the similarities in early embryonic development, such contemporary critics argue that Haeckel alters the scale of his drawings to enhance such similarities as well. Contemporary comparisons of representations of true developing embryos to Haeckel's embryo drawings confirms the falsification of Haeckel's embryo drawings of early embryonic development, noting inherent differences between the developing embryos of different species. Due to Haeckel’s fraudulent representations of embryonic development, his contemporaries are somewhat astonished at the prevalence of renditions of his embryo drawings in modern biology and science textbooks and the continual deception of the world of science.

Ernst Haeckel (1834-1919)
Figure 1: Ernst Haeckel.

Most of the work in the drawings of embryological development has depended upon such illustrations produced by Ernst Haeckel, who posits the practice of comparative embryology. The study of comparative embryology is based upon the belief that all vertebrate embryos follow a common developmental path due to their common ancestry. Such developing vertebrates have similar genes, which determine the basic body plan. However, further development allows for the distinguishing of distinct characteristics as adults. Haeckel’s embryos are illustrated with plates showing vertebrate embryos at different stages of development, which ultimately exhibit embryonic resemblance as proof of Darwinian evolution, recapitulation as proof of the Biogenetic Law, and phenotypic divergence as proof of von Baer’s laws. The series of twenty-four embryos from the early editions of Haeckel’s Anthropogenie remain the most famous, and those embryo drawings most often reproduced in modern books. However, Haeckel’s first illustrations of vertebrate embryos appeared in the Naturliche Schopfungsgeschichte. Haeckel claims to have published his drawings of vertebrate embryos due to direct observation of the fish, salamander, tortoise, chick, hog, calf, rabbit, and man at three successive stages of development. The different species are arranged in columns relative to one another, and the different stages in rows. According to Haeckel’s embryo drawings, he portrays embryonic resemblance in the first row and phenotypic divergence in the final rows. As well, the appearance of specialized characters in each species can be witnessed through vertical interpretation of his drawings. Diagonal interpretation leads one to Haeckel’s idea of recapitulation. Haeckel’s portrayal of recapitulation simply concerns adult characteristics in his embryo drawings, rather than full stages of embryonic development.



Figure 2: Haeckel's embryos are (left to right) of the fish, salamander, tortoise, chick, hog, calf, rabbit, and human.

Haeckel’s embryo drawings express his commitment to Darwin’s theory of evolution and descent. Haeckel strongly believed that the manifestations of key principles of variability and heritability influenced the operation of natural selection. His postulation of embryonic development coincides with his understanding of evolution as a developmental process. In and around 1800, embryology fused with comparative anatomy as the primary foundation of morphology. Morphology represents a study of the form or shape of an organism throughout the stages of development. Ernst Haeckel, along with Karl von Baer and Wilhelm His, are primarily influential in forming the preliminary foundations of ‘phylogenetic embryology’ based on principles of evolution. Haeckel’s ‘Biogenetic Law’ portrays the parallel relationship between an embryo’s development and phylogenetic history. The term, ‘recapitulation,’ has come to embody Haeckel’s Biogenetic Law, for embryonic development is a recapitulation of evolution. Haeckel proposes that all classes of vertebrates pass through an evolutionarily conserved “phylotypic” stage of development, a period of reduced phenotypic diversity among higher embryos. Only in later development do particular differences appear. Haeckel portrays a concrete demonstration of his Biogenetic Law through his ‘Gastrea’ theory, in which he argues that the early cup-shaped gastrula stage of development is a universal feature of multi-celled animals. An ancestral form existed, known as the gastrea, which was a common ancestor to the corresponding gastrula.

Haeckel argues that certain features in embryonic development are conserved and palingenetic, while others are caenogenetic. Caenogenesis represents “the blurring of ancestral resemblances in development,” which are said to be the result of certain adaptations to embryonic life due to environmental changes. In his drawings, Haeckel cites the notochord, pharyngeal arches and clefts, pronephros and neural tube as palingenetic features. However, the yolk sac, extra-embryonic membranes, egg membranes and endocardial tube are considered caenogenetic features. The addition of terminal adult stages and the telescoping, or driving back, of such stages to descendant’s embryonic stages are likewise representative of Haeckelian embryonic development. In addressing his embryo drawings to a general audience, Haeckel does not site any sources, which gives his opponents the freedom to make assumptions regarding the originality of his work.

Karl E. von Baer (1792-1876)
Although Haeckel’s drawings have become the center of controversy for decades, he was not the sole person to create a series of drawings representing embryonic development. Karl E. von Baer and Haeckel both struggled to model one of the most complex problems facing embryologists at the time: the arrangement of general and special characters during development in different species of animals. In relation to developmental timing, von Baer's scheme of development differs from Haeckel's scheme. Von Baer's scheme of development need not be tied to developmental stages defined by particular characters, where recapitulation involves heterochrony. Heterochrony represents a gradual alteration in the original phylogenetic sequence due to embryonic adaptation. As well, von Baer early noted that embryos of different species could not be easily distinguished from one another as in adults. Although Haeckel’s laws are ‘recapitulationary’ and ‘evolutionary,’ von Baer’s laws governing embryonic development are specific rejections of recapitulation. Von Baer specifically acknowledges the influence of recapitulation’s dominant idea that embryos of higher animals pass through the permanent forms of lower animals. As a response to Haeckel’s theory of recapitulation, von Baer enunciates his most notorious laws of development. Von Baer’s laws state that general features of animals appear earlier in the embryo than special features, where less general features stem from the most general, each embryo of a species departs more and more from a predetermined passage through the stages of other animals, and there is never a complete morphological similarity between an embryo and a lower adult. Von Baer’s embryo drawings display that individual development proceeds from general features of the developing embryo in early stages through differentiation into special features specific to the species, establishing that linear evolution could not occur. Embryological development, in von Baer’s mind, is a process of differentiation, “a movement from the more homogeneous and universal to the more heterogeneous and individual.” Although this argument seems consistent with Haeckel’s theory of recapitulation, von Baer proceeds to argue that embryos will resemble each other prior to attaining characteristics differentiating them as part of a specific family, genus or species, but do not parallel permanent forms of lower organisms in this process.

Wilhelm His (1831-1904)
Wilhelm His was one of Haeckel’s most authoritative and primary opponents advocating physiological embryology. His Anatomie menschlicher Embryonen (Anatomy of human embryos) employs a series of his most important drawings chronicling developing embryos from the end of the second week through the end of the second month of pregnancy. His, in opposition to Haeckel, seeks to take human embryos out of the hands of Darwinist proponents. In 1878, His begins to engage in serious study of the anatomy of human embryos for his drawings. During the nineteenth century, embryologists often obtained early human embryos from abortions and miscarriages, postmortems of pregnant women and collections in anatomical museums. In order to construct his series of drawings, His collects specimens in which he manipulates them into a form with which he can operate.

In His’ Normentafel, he displays specific individual embryos rather than ideal types. His does not produce norms from aborted specimens, but rather visualizes the embryos in order to make them comparable and specifically subjects his embryo specimens to criticism and comparison with other cases. Ultimately, His’ critical work in embryonic development comes with his production of a series of embryo drawings of increasing length and degree of development. His’ depiction of embryological development strongly differs from Haeckel’s depiction, for His argues that the phylogenetic explanation of ontogenetic events is unnecessary. His argues that all ontogenetic events are the “mechanical” result of differential cell growth. His’ embryology is not explained in terms of ancestral history.



Figure 3: The His Normentafel.

The debate between Haeckel and His ultimately becomes fueled by the description of an embryo that Wilhelm Krause propels directly into the ongoing feud between Haeckel and His. Haeckel speculates that the allantois is formed in a similar way in both humans and other mammals. His, on the other hand, accuses Haeckel of altering and playing with the facts. Although Haeckel is proven right about the allantois, the utilization of Krause’s embryo as justification turns out to be problematic, for the embryo is that of a bird rather than a human. The underlying debate between Haeckel and His derives from differing viewpoints regarding the similarity or dissimilarity of vertebrate embryos. In response to Haeckel’s evolutionary claim that all vertebrates are essentially identical in the first month of embryonic life as proof of common descent, His responds by insisting that a more skilled observer would recognize even sooner that early embryos can be distinguished. His also counteracts Hacekel’s sequence of drawings in the Anthropogenie with what he refers to as “exact” drawings, highlighting specific differences. Ultimately, His goes so far as to accuse Haeckel of “faking” his embryo illustrations to make the vertebrate embryos appear more similar than in reality. His also accuses Haeckel of creating early human embryos that he conjured in his imagination rather than obtained through empirical observation. His completes his denunciation of Haeckel by pronouncing that Haeckel had “‘relinquished the right to count as an equal in the company of serious researchers.’”

Opposition to Haeckel
Haeckel encountered numerous oppositions to his theories and artistic depictions of embryolonic development as proof of Darwinian evolution during the late nineteenth and early twentieth centuries. Haeckel’s opponents believe him to have committed intentional “fraud” in his embryo drawings, arguing that he de-emphasizes the differences between early embryonic stages in order to make the similarities seem more pronounced. Many of his opponents at the time argue that Haeckel’s drawings are either confirming of pre-existing knowledge, or simply represent a clash with more advanced understanding of embryological development.

Early Opponents: Carl Semper, Theodor Bischoff, Albert Kölliker, and Rudolph Virchow
Carl Semper (1832-1893), on the one hand, was an evolutionary and a particularly dangerous enemy. Semper argues that Haeckel’s sin lies in comparative anatomy’s interpretation of embryology. Semper particularly exposes the dogmatism in Haeckel’s work, referring to Haeckel’s gastrea theory as an example of his dogmatic attitude. Haeckel's gastrea theory, according to Semper, imposes dogmatic theory onto empirical observations. Theodor Bischoff (1807-1882), most widely known for his hostility toward women’s medical education, is a strong opponent of Darwinism. As the pioneer in mammalian embryology, he is one of Haeckel’s strongest critics. Although Bischoff’s 1840 surveys depict how similar the early embryos of man are to other vertebrates, he later demands that such hasty generalization was inconsistent with his recent findings regarding the dissimilarity between hamster embryos and those of rabbits and dogs. Nevertheless, Bischoff’s main argument was in reference to Haeckel’s drawings of human embryos, for Haeckel is later accused of miscopying the dog embryo from him. Albert Kölliker (1817-1905), who likewise criticizes Haeckel’s evolutionary interpretation of embryological development, is opposed to the idea of descent from a common ancestor in favor of his belief in development along distinct and separate lines. Such is true, for Kölliker strongly rejects the belief in human descent from apes. Throughout Haeckel’s time, criticism of his embryo drawings was often due in part to his critic’s belief in his representations of embryological development as “crude schemata.” In this way, Haeckel specifically selects relevant features to portray in his drawings. Haeckel’s opponents find his method problematic because such simplification eliminates certain structures that differentiate between higher and lower vertebrates. In 1877, Rudolph Virchow (1821-1902), once an inspiration to Haeckel at Würzburg, proclaims that Haeckel’s embryo drawings represent mere hypotheses. The teaching of hypotheses in schools would ultimately serve to severely endanger the future of science.

Haeckel's First Charge of Fraud (1868)
The first forgery charges against Haeckel are introduced in late 1868 by Ludwig Rutimeyer in the Archiv fur Anthropogenie. As a professor of zoology and comparative anatomy at the University of Basel, he rejects the concept of natural selection as simply mechanistic and proposes an anti-materialist view of nature. Against Haeckel’s embryological drawings, Rutimeyer argues that Haeckel “had taken to kinds of liberty with established truth.” Rutimeyer primarily insists upon illustrations modeled after specimens and argues that Haeckel presents an incorrectly interpreted woodcut three consecutive times with different captions of the embryo of the dog, chick, and turtle. Ultimately, Rutimeyer denies such drawings any sincere originality. Although Rutimeyer does not outwardly denounce Haeckel’s embryo drawings as forgery or fraud, he argues that such drawings are rather playful manipulations of public and scientific thought.

Contemporary Opposition to Haeckel: Icons of Evolution by Jonathan Wells


Figure 4: Jonathan Wells' Icons of Evolution.

Contemporary opponents of Haeckel have recently voiced their denunciation of his fraudulent embryo drawings. Published in 2000, Wells' book, Icons of Evolution, attempts to overthrow the evolutionary model by attacking the means by which evolution is taught. One of Wells’ icons is that of Haeckel’s embryo drawings. Wells notes how widely distributed Haeckel’s embryo drawings are in modern textbooks dealing with evolution, but argues that biologists have known for over a century that Haeckel merely faked these drawings. As well, he notes that the stage Haeckel deemed to be the first is actually midway through development and the earliest stages of development are not the most similar. Wells argues that fertilization begins with a process called “cleavage,” which then leads to “gastrulation.” The two combined processes are ultimately responsible for establishing the animal’s general body plan. In Haeckel’s embryo drawings, only after cleavage and gastrulation does the embryo reach the stage that he labels as the first. If the embryos are similar during the early stages of development, the various classes of embryos would be most similar during cleavage and gastrulation. However, it has been determined in a survey of the classes of bony fish, amphibians, reptiles, birds, and mammals that this is not the case. As well, Wells argues that Haeckel often uses the same woodcut for embryos of different classes and alters the drawings to make the embryos appear more similar. Haeckel’s embryo drawings are intended to support his biogenetic law. However, Wells argues that Haeckel’s biogenetic law is simply inferred from evolutionary theory rather than empirical observation.

Contemporary Opposition to Haeckel: Michael Richardson and Stephen Jay Gould
Michael Richardson and his colleagues in an August 1997 issue of Anatomy & Embryology, shows that Haeckel fudges his drawings in order to exaggerate the similarity of the phylotypic stage. Richardson and his colleagues compare Haeckel’s embryos to photographs of actual embryos from all seven classes of vertebrates and find that Haeckel’s drawings clearly misrepresent the truth. As well, Richardon notes that vertebrate embryos vary significantly in size and in the number of somites. In a March 2000 issue of Natural History, Stephen Jay Gould argues that Haeckel “‘exaggerated the similarities by idealizations and omissions.’” As well, Gould argues that Haeckel’s drawings are simply inaccurate and falsified. Despite the outright criticisms and denunciations of Haeckel’s drawings of embryological development, some version of Haeckel’s drawings can be found in modern biology textbooks. Gould ultimately argues that one has the right to be “‘both astonished and ashamed by the century of mindless recycling that has led to the persistence of these drawings in a large number, if not a majority, of modern textbooks.’”

Haeckel's Proponents (Past and Present)
Despite the numerous oppositions, Haeckel has influenced many disciplines in science in his drive to integrate such disciplines of taxonomy and embryology into the Darwinian framework and to investigate phylogenetic reconstruction through his Biogenetic Law. As well, Haeckel served as a mentor to many important scientists, including Anton Dohrn, Ricard and Oscar Hertwig, Wilhelm Roux, and Hans Driesch.

One of Haeckel's earliest proponents is Carl Gegenbaur at the University of Jena (1865-1873), during which both men are absorbing the impact of Darwin's theory. The two quickly sought to integrate their knowledge into an evolutionary program. In determining the relationships between "phylogenetic linkages" and "evolutionary laws of form," both Gegenbaur and Haeckel rely on a method of comparison. As Gegenbaur argues, the task of comparative anatomy lies in explaining the form and organization of the animal body in order to provide evidence for the continuity and evolution of a series of organs in the body. Haeckel then provides a means of pursuing this aim with his biogenetic law, in which he proposes to compare an individual's various stages of development with its ancestral line. Although Haeckel stresses comparative embryology and Gegenbaur promotes the comparison of adult structures, both believe that the two methods could work in conjunction to produce the goal of evolutionary morphology.

The philologist and anthropologist, Friedrich Müller, uses Haeckel's concepts as a source for his ethnological research, involving the systematic comparison of the folklore, beliefs and practices of different societies. Müller's work relies specifically on theoretical assumptions that are very similar to Haeckel's and reflects the German practice to maintain strong connections between empirical research and the philosophical framework of science. Language is particularly important, for it establishes a bridge between natural science and philosophy. For Haeckel, language specifically represents the concept that all phenomena of human development relate to the laws of biology. Although Müller does not specifically have an influence in advocating Haeckel's embryo drawings, both share a common understanding of development from lower to higher forms, for Müller specifically sees humans as the last link in an endless chain of evolutionary development.

Modern acceptance of Haeckel's Biogenetic Law, despite current rejection of Haeckelian views, finds support in the certain degree of parallelism between ontogeny and phylogeny. A. M. Khazen, on the one hand, states that "ontogeny is obliged to repeat the main stages of phylogeny." A. S. Rautian, on the other hand, argues that the reproduction of ancestral patterns of development is a key aspect of certain biological systems. Dr. Rolf Siewing acknowledges the similarity of embryos in different species, along with the laws of von Baer, but does not believe that one should compare embryos with adult stages of development. According to M. S. Fischer, reconsideration of the Biogenetic Law is possible as a result of two fundamental innovations in biology since Haeckel's time: cladistics and developmental genetics.

In defense of Haeckel's embryo drawings, the principal argument is that of "schematisation." Haeckel's drawings are not intended to be technical and scientfic depictions, but rather schematic drawings and reconstructions for a specifically lay audience. Therefore, as R. Gursch argues, Haeckel's embryo drawings should be regarded as "reconstructions." Although his drawings are open to criticism, his drawings should not be considered falsifications of any sort. Although modern defense of Haeckel's embryo drawings still considers the inaccuracy of his drawings, charges of fraud are considered unreasonable. As Erland Nordenskiöld argues, chargues of fraud against Haeckel are unnecessary, despite the fact that his drawings are falsified and not derived from real specimens. R. Bender ultimately goes so far as to reject His's claims regarding the fabrication of certain stages of development in Haeckel's drawings, arguing that Haeckel's embryo drawings are faithful representations of real stages of embryonic development in comparison to published embryos.

The Survival and Reproduction of Haeckel's Embryo Drawings
Haeckel's embryo drawings, as comparative plates, are first only copied into biology textbooks, rather than texts on the study of embryology. Even though Haeckel's program in comparative embryology virtually collapses after the First World War, his embryo drawings have often been reproduced and redrawn with increased precision and accuracy in works that have kept the study of comparative embryology alive. Nevertheless, neither His-inspired human embryology nor developmental biology are concerned with the comparison of vertebrate embryos. Ultimately, controversies over embryo illustrations slips out of memory. Although Stephen Jay Gould's 1977 book, "Ontogeny and Phylogeny," helps to reassess Haeckelian embryology, he avoids addressing the controversey over Haeckel's embryo drawings. Nevertheless, new interest in evolution in and around 1977 inspires developmental biologists to look more closely at Haeckel's illustrations that they perceive to be littering and exploiting their textbooks. Ultimately, Haeckel's illustrations of vertebrate embryos survive in order to promote embryological depictions of pregnancy as well as the history of life on earth. Such fraudulent drawings continue to be reproduced in modern biology textbooks, for those in opposition are simply dismissed as critics of Darwin and evolution. Nevertheless, it can be said that once Haeckel's embryo drawings are removed from modern texts, they could potentially have the most to teach about the importance of precision and accuracy in modern scientific research.