Embryonic Evolution Through Ernst Haeckel’s Eyes

The 19th century biologist’s drawings, tainted by scandal, helped bolster, then later dismiss, his biogenetic law.

By | May 1, 2017

EMBRYONIC EVOLUTION: This comparative illustration of eight species’ embryos from Haeckel’s Anthropogenie (1874 edition) is among the most well-known of the German scientist’s images. The rows represent three developmental stages and the columns correspond to different species (fish, salamander, turtle, chicken, pig, cow, dog, and human). NICK HOPWOOD

Ernst Haeckel, a biologist, artist, and philosopher born in Prussia in the 1830s, played a key role in spreading Darwinism in Germany. He was also deeply fascinated by embryology and illustrated some of the most remarkable comparisons of vertebrate embryos in his day. These images were widely printed and copied, both to argue for Haeckel’s controversial evolutionary theories and to debunk them.

Haeckel’s most influential idea was his now-infamous biogenetic law, summarized by the phrase “ontogeny recapitulates phylogeny”—in other words, an organism’s embryo progresses through stages of development that mirror its evolutionary history. According to this theory, embryos of more advanced species—humans, for example—would pass through stages in which they displayed the adult characteristics of their more primitive ancestors (such as fish gills or monkey tails).

The biogenetic law was popular among scientists at the time, including Darwin, and Haeckel used his drawings of embryos to support his own theory. His textbook on comparative embryology, Anthropogenie—in which he published some of his most famous illustrations of embryos—was devoted to this idea, says Nick Hopwood, a historian of science and medicine at the University of Cambridge and author of Haeckel’s Embryos: Images, Evolution and Fraud, published in 2015.

A number of Haeckel’s contemporaries, such as Wilhelm His Sr., a Swiss anatomist, challenged the biogenetic law and alleged that Haeckel’s drawings contained inaccuracies and misleading representations. One such accusation was that Haeckel had reprinted a single woodcut to create illustrations of a mammal, a bird, and a reptile in his first book, Natürliche Schöpfungsgeschichte. Haeckel admitted to this malpractice and apologized for it in a later edition of the book.

See “Ernst Haeckel’s Pedigree of Man, 1874

Haeckel’s embryo drawings were widely circulated. They appeared in some mid-20th century high school and college biology textbooks in the United States, often bearing the name of a Canadian-British evolutionary biologist and physiologist, George John Romanes, who had copied Haeckel’s work. Authors and publishers used Romanes’s facsimile to dispute Haeckel’s own theories, unaware that Haeckel himself had drawn the original content, Hopwood says.

In later years, Haeckel’s original images reappeared, this time in the developmental biology literature, often to argue for similarities across species during embryonic growth. Although biologists still criticized the drawings for containing inaccuracies, the idea that early commonalities exist more closely aligns with what scientists believe today.

“We now think that embryos resemble not the adults of ancestral species, but the embryos of ancestral species,” Michael Richardson, a professor of evolutionary developmental zoology at Leiden University in the Netherlands, wrote in an email. He adds that there is still the belief among biologists that a “phylotypic period,” when embryos share strong similarities across species, exists, as Haeckel often demonstrated in the top row of his drawings. However, according to Richardson, more recent evidence points to commonalities at the molecular level.

“I think it’s fascinating that [Haeckel’s drawings] are some of the most controversial pictures in the history of science and yet became some of the most routinely used,” Hopwood says.

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Avatar of: JimM

JimM

Posts: 6

May 8, 2017

They were controversial because they were not true and were used to prop up in particular Darwin's theory. They were thoroughly discredited by the 1920's even before Mendel's work on genetics was done by embroyologists, but as the article said were still being used as "proof" of Darwin's particular take on evolution at least into the 60s where I saw them in a textbook and nary a word about the controversy or just really a bald faced hoax no less than the Piltdown hoax. Science would not be losing its prestige if its scientists would stop using science to put forth a political or metaphysical agenda. Two fields in which science has no empirics to back it up with any authority. Political science isn't science it is just opinions, some are true, but some are not. Not very scientific.

Avatar of: Salticidologist

Salticidologist

Posts: 40

May 16, 2017

One can argue the precise meaning of "ontogeny recapitulates phylogeny," but recent discoveries in the area of research called "evo/devo" or evolutionary development have given us much more understanding of why Haeckel's patterns were important.  As noted in the quote from Richardson, the similarities of developmental stages are real.  In fact they can be quite the same (homologous) as evolution proceeds through the modification of developmental processes as a result of genetic changes.  Some of the features that contributed to the air-breathing of a bony fish that came to the surface to swallow air can now be seen in mammals, where we must live with a poor design that joins our breathing with our feeding.

Avatar of: Andy Brower

Andy Brower

Posts: 7

May 16, 2017

This oft-repeated refrain is an unfair representation of Haeckel and his immense contributions to comparative anatomy, developomental biology and our understanding of phylogeny (a word which Haeckel coined).  The drawings of comparative stages of embryonic development are not intended to be "realistic," any more than are illustrations of a heart in a modern physiology textbook, with red arteries and blue veins.  They were intended to illustrate heuristically the features shared among different kinds of vertebrates at different stages of development.  The general principle of this is called Von Baer's law, after Karl Von Baer, the first person to suggest it, in the 1820's and it is still considered true today.  Embryos of all kinds of animals start out as a zygote, the cells divide to form a blastula, and then how this invaginates and differentiates to form a gastrula with different embryonic tissue types establishes the difference between protostomes and deuterostomes.  Later on, the basic anterior-posterior axis forms, and limbs or fins, etc.  Human embryos have a tail, a notochord and gill slits, for a while, as do all chordates.

As far as I can see, none of the embryos in the above illustration looks like an adult form of any other species, and really the connection between this picture and the biogenetic law is spurious (perhaps Haeckel made that argument, but it is not intrinsic to the diagram itself).

For more detailed and nuanced information on this topic, see the following books:

Amundson, R. 2005. The Changing Role of the Embryo in Evolutionary Thought:  Roots of Evo-Devo. Cambridge University Press, Cambridge.
 

Rieppel, O. 2016. Phylogenetic systematics:  Haeckel to Hennig. CRC Press, Boca Raton, FL.
 

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