Haeckel’s Embryos and Theistic Idiocy

Posted on February 23, 2012

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Originally posted on An American Atheist.

I am not sure if Creationists will ever stop beating this dead horse.

For whatever reason, WordPress is not allowing me to embed a video as it did on An American Atheist.  Please watch the video located HERE, and then continue reading.

Many theists, such as those involved in the production in the above video, and many more, are of the opinion that if one thing is shown to be wrong about evolution at any time in the past, then everything must be thrown out because how could we possibly trust these conniving evolutionists anymore about anything else?  The man in the above video is talking about an old controversy within evolutionary biology and developmental biology.  He is talking about Ernst Haeckel, an 18th and early 19th century biologist.  The controversy around Haeckel had to do with his pet hypothesis that the stages of development an embryo undergoes during gestation reflect past evolutionary forms.  You may have heard this concept formulated as “ontogeny recapitulates phylogeny.”  Ontogeny refers to the growth and development of an individual during its lifetime, and phylogeny refers to evolution, i.e., phenotypic changes that take place over generations as opposed to changes during an organism’s lifetime as it develops from a zygote on through adulthood.

Haeckel's embryos.

This idea was first proposed by Charles Darwin in his groundbreaking book On the Origin of Species, and Haeckel quickly adopted and spread this view.  Haeckel, who studied the development of many different taxa and was quite an artist, published a book complete with original drawings showing the similarities between the developmental stages of these widely different creatures.  These famous drawings came to be known as “Haeckel’s embryos,” and they were later shown to be fudged, or rather Haeckel took it upon himself to stretch the truth and make the drawings reflect his personal bias for a pet theory rather than reality.

It’s always disappointing when a scientist is found to be fraudulent, because their individual actions are, without exception, blown up by anti-evolutionists as proof that evolution, as a whole, is one big hoax.  Their argument goes something like this:

  1. A biologist claimed that X happens and X is evidence for evolution.
  2. The biologist was dishonest and his claim X was shown to be false.
  3. Therefore, all biologists are dishonest, and there is no evidence for evolution.

Despite what these theists think, to have one proposed case as evidence for evolution rebuked in no way does away with the gargantuan stockpile of evidence for evolution coming from other fields of biology.  Does the fact that ontogeny doesn’t recapitulate phylogeny undermine the evidence for evolution from population genetics, ecology, biogeography, paleontology, and molecular biology?  No, not even the slightest bit!  And what makes the claim that evolution is a hoax because of Ernst Haeckel’s flub even more ridiculous is that, although ontogeny doesn’t recapitulate phylogeny, per se, there are still many developmental pathways that are constrained by ancestry to proceed down a predetermined route, only to be modified later in development.  Haeckel’s ideas can be thought of as a “strong” version for recapitulation–that stages of development represent the actual adult forms of evolutionary history.  While this concept is not accepted by modern biologists, a weaker version of this idea is widely accepted as true.

Fore and hind limbs of a developing dolphin.

There are many examples of phenotypic modifications taking place after development has been allowed to run its course for a while (i.e., after a basic body plan has been laid down).  An example of this is the fact that snakes and cetaceans (whales and dolphins)—all legless organisms thought to have evolved from tetrapod (four-legged) ancestors—develop limb buds during development, only to have them reabsorbed later on.  This is indicative of the fact that snakes and cetaceans are tetrapods that have only recently lost limbs due to directional selection for limb reduction.  The genetic modifications in development for limb reduction happen to take place after limb buds are formed instead of before.  This is because selection only discriminates on whether or not the end product is a limbless whale that is more streamlined, rather than how exactly it got that way developmentally.  Modification happening before or after limb buds are formed is essentially irrelevant.  So, although Haeckel altered a few drawings and pushed his ideas too hard, the concept biologists work with today bears the mark of Haeckel–we can learn something about an organism’s evolutionary past from studying embryonic development, but what we do not see is a full representation of every adult phenotype its ancestors have ever possessed.

If Haeckel is even mentioned in biology textbooks today (and it is a very rare occurrence) it is to give our current understanding of development a historical context.  No modern textbook holds Haeckel’s ideas in their original formulation to be pervasive in modern biological thought, nor do they wish it to be.

So why do Creationists and other religious conservatives keep bringing up Haeckel’s embryos?  Because, apart from Piltdown Man (another hoax), it’s all they’ve got as ammunition in their anti-evolution quivers.  Since they lack any robust argument against modern evolutionary theory, they attack small bumps in its history, and shout about them from the rooftops in hopes that somebody will take them seriously—and people do!  I have had Haeckel’s embryos brought up numerous times while conversing with religious people who have been taught that Haeckel was wrong, wrong, wrong.  They think that I am falling into their carefully crafted trap when I start talking about how his ideas are not totally irrelevant in modern developmental biology today.  It really only amounts to a greater exposure of their own ignorance and failure to fully research and understand a subject they are desperately trying to invalidate.  Hopefully, after reading this, you feel better equipped in arguing with theists on this topic; it’s in their arsenal, and so it should be in yours.

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Posted in: Atheism, Religion, Science