Saving Haeckel: Why “Ontogeny Recapitulates Phylogeny” Isn’t so Wrong

Saving Haeckel: Why “Ontogeny Recapitulates Phylogeny” Isn’t so Wrong August 10, 2017

Ernst Haeckel was an influential German scientist who supported Charles Darwin’s theory of evolution. He published his influential theory of embryology, distilled as “ontogeny recapitulates phylogeny” in 1866, seven years after Darwin’s On the Origin of Species. Haeckel’s theory fell out of favor and hasn’t been part of evolutionary theory for many decades, but it’s still cited today as a cause of mischief by modern Creationists.

Haeckel’s theory

The similarities between embryos of different animal species were noted decades before Darwin: while adults of different species are easy to tell apart, their embryos are not. Haeckel took this further and is most known for his 1874 drawing (above) of the development of various animal embryos—fish, chicken, human, and so on—to illustrate his point.

Ontogeny is the development of an embryo, and phylogeny is an organism’s evolutionary history. So by “ontogeny recapitulates phylogeny,” Haeckel was saying that you can watch through an organism’s development as an embryo a replay of its development through hundreds of million years of evolution. For example, a human embryo first looks like a fish (notice the gill-like structure), then like a reptile (four limbs and a tail), and finally like a mammal, which is the evolutionary path that humans took.

But it doesn’t work like that.

What embryology actually tells us

Let’s put Haeckel aside for now and look for clues to evolution within embryology. What’s fascinating is how embryonic structures that developed in animals that preceded humans, like fish and reptiles, have been repurposed by evolution for humans.

Pharyngeal arches or folds (often improperly called “gill slits”) are the double-chin-like folds under the head in the early embryo stage. This striking visual commonality is found in all vertebrate embryos.

The arches that develop into gills in fish become various cartilages, glands, muscles, and other tissue in the human neck and face.

These arches explain the strange path of the recurrent laryngeal nerve. Pharyngeal arches four, five, and six (arch one is closest to the head) fuse early in the development of mammal embryos. The recurrent laryngeal nerve comes from the fourth arch, and after the fusion, it is near an artery from the sixth arch. This creates a straightforward layout in fish, but in mammals the neck takes the brain and larynx (connected by this nerve) away from the heart. The problem is that the nerve is hooked around that artery. That means that in all mammals—yes, even the long-necked giraffe—the nerve goes from the brain, down around this artery, and back up to the larynx. No perfect designer would create this, but it is nicely explained by evolution.

Another example of repurposing (technically, exaptation) is the mammalian ear. Structures that develop into a multi-bone jaw in reptiles have been repurposed to become ear bones in mammals. In fact, it was embryology, not fossils, that provided the first clues of this evolution.

The Creationists

Creationists respond that the perfect designer was making variations on a theme. If you’ve got a great design, why design everything from scratch? Why not simply tweak it for various environments? This designer is like a car company that makes small cars (shrews, mice) and big ones (elephants, whales), cars that are beautiful (peacock, gazelle) and cars for tough environments (camel, yak).

In the first place, the supernatural assumption adds nothing when we have a natural theory that explains evolution just fine. “God” is a solution looking for a problem, and we don’t have a problem here.

And second, if land animals are like cars, why do they begin life looking like submarines? (h/t Troy Britain)

See also: Argument from Design BUSTED!

Another obvious similarity across early embryos is the tail. Human embryonic tails are absorbed later in development. The hind limbs of cetaceans like whales also appear in embryos and are likewise absorbed.

If you saw the movie Avatar, did you catch the evolution mistake it makes? The land animals had six limbs and breathed through a second mouth on their shoulders. The winged creatures also had six limbs—four legs and two wings. But the Na’vi people had four limbs and no shoulder mouths. If they had a common ancestor with the other animals of their world, like people on earth, you would see these fundamental characteristics shared.

Ah, well—Hollywood.

Creationism’s failure

Why do adult animals differ in appearance but look similar as embryos? Why should the same basic embryonic components become gills in fish but faces in mammals? Why do human embryos have a tail that is later reabsorbed? The common beginning as early embryos and later divergence to satisfy different body plans points to common ancestry, not design. Evolution explains all this nicely, while Creationism has no explanation.

The Creationist play book is to attack evolution, usually by asking questions that are important but already answered. Biologists have a ready answer, but these questions stump the average person, which is the target audience.

Even if Creationism’s questions were new and insightful (they never are), Creationism doesn’t become the dominant scientific paradigm by showing flaws in evolution; it could only do that by explaining the evidence better. But since Creationists are only pretending to be scientific, playing by science’s rules is never the goal. Creationists don’t participate in the domain of regular biology, which includes conferences, journals, and laboratories. They’ve already lost there, and that’s been true for a century. So they peddle their message exclusively to the public, another admission that they aren’t doing science.

Yes, Haeckel was wrong, and his error, like any popular wrong turn, delayed progress. But evolution was never built with this as part of its foundation. Turn back humans’ evolutionary clock and we see the tail grows back (as in other mammals), the ear bones become jaws (as in reptiles), and the throat becomes gills (as in fish). Haeckel got a lot wrong, but he was right that embryology holds clues to where we came from.

(h/t commenter MR for links to articles)

Acknowledgements: these excellent articles were helpful in writing this post.

Somebody’s gotta stand up to experts.
Don McLeroy, Texas board of education,
speaking against evolution in public schools

Image credit: Wikimedia

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  • Otto T. Goat
  • Bob Jase

    Haeckel delayed progress for a few decades, religion has delayed progress since it was invented a few thousand years ago – no contest.

  • Jim Jones

    Haeckel was sort of right except it’s just another example of evolution reusing stuff that existed. And also why men have nipples.

    • I’ve also heard that that’s why females have orgasms–it’s necessary for males to, and it became a freebie for females.

      • Greg G.

        I have heard that the purpose of orgasms is to let the male know when to stop fucking.

  • Pofarmer

    And still no recent comments. WTF Patheos?

    • epeeist

      As I have said elsewhere, given that I live in a different time zone to many other commenters here I rely on the “Recent Comments” to keep me up to speed with what is going on. I don’t have the time or inclination to look at each and every article to see whether there is a new comment or not, especially with the oubliette that is Disqus.

      • Pofarmer

        And still nothing. they’ve broke something that wasn’t. Comments load a little better, but there won’t be nearly as many of them.

        • Greg G.

          Try this:

          Copy the code and paste it to Notepad. Save the file as “CE.html” or anything you like. The “.htm” or “.html” tells your computer which program to open it with.

          Open it with your browser. It gives 25 comments with up to 400 characters each. Depending on the browser, you can click either the time stamp or the respondent’s name. Chrome works with the time stamp. I like to right click and open a new tab.

        • epeeist

          I note that at the time of this post the article has 13 comments and 5 of these are complaining about the breakage.

        • I’ve put Greg G’s code in a page at this blog:

          It should work like the previous list. With the new default formatting, it ain’t pretty, but it works.

          If you ever forget the link, I’ve put that at the bottom of the Haeckel post (this one).

          That’s pretty cludgy, but thanks, Greg, for making it a lot better than nothing. I’ve told Patheos about the torches and pitchforks here on this subject.

  • Kevin K

    Haekel’s observations weren’t wrong…his conclusions were. There’s a difference.

    And, of course, the thing about the creationist mindset is that once something is said, that’s it … forever and ever set in stone, never to be modified, or even overturned by better evidence. They obsess over the early scientists of the 18th and 19th centuries, never mind that the vast majority of scientific progress in virtually every discipline you care to mention has been made in the past 50 years. Including the biological sciences.

    • Michael Neville

      Haeckel died just over 99 years ago. Creationists are still using him as “evidence” against evolution.

      • Kevin K

        Yes, they’re stuck in the 1800s. Science, however, moves apace.

  • RichardSRussell

    An excellent book that reviews where all of these human characteristics originated is Richard Dawkins’s The Ancestor’s Tale, which was modeled on Geoffrey Chaucer’s The Canterbury Tales in that they are stories told on a journey. Only, in the Dawkins book, the journey is an imaginary one back thru time, up the trail on the great Tree of Life that led humans to become what they are today. Coming down the tree, of course, different species split off from our line, but going in reverse, back up the tree, it appears that they are joining the party of travelers, each telling its tale upon arrival.

  • 🙂

  • epeeist

    Total aside, but what sort of thing are we going to get from this coupling:

    (From this article)