Countering Creationism, Part IV: Carl Sagan & Development

17 05 2007

Carl Sagan, for most of his professional career, never said the one phrase that was most identified with him. Even today I can scarcely say the word “billion” without a memory of Cosmos or something gleaned from The Demon Haunted World creeping in from the recesses of my brain, but Sagan never joined the first billion with another until he published the book Billions and Billions in 1997. Describing this anomaly in the book’s introduction, Sagan writes;

I never said it. Honest. Oh, I said there are maybe 100 billion galaxies and 10 billion trillion stars. It’s hard to talk about the Cosmos without using big numbers. I said “billion” many times on the Cosmos television series, which was seen by a great many people. But I never said “billions and billions.” For one thing, it’s too imprecise. How many billions are “billions and billions”? A few billion? Twenty billion? A hundred billion? “Billions and billions” is pretty vague. When we reconfigured and updated the series, I checked- and sure enough, I never said it.

Sagan goes on to note how there are certain apocraphyal sayings that follow certain figures around, “Sherlock Holmes never said ‘Elementary, my dear Watson’ (at least in the Arthur Conan Doyle books); Jimmy Cagney never said, ‘You dirty rat’; and Humphrey Bogart never said, ‘Play it again, Sam,'” but in today’s essay we’re more concerned with something a little more subtle. Paul Humbert brings us the follow creationist claim for this installment;

Reason #9: Related to the above, Carl Sagan encouraged the fiction that life in the womb traces out an evolutionary history. We “must decide,” he wrote, “what distinguishes a human being from other animals and when, during gestation, the uniquely human qualities—whatever they are—emerge.” He compared the appearance of the developing embryo to “a segmented worm” and added that “something like the gill arches of a fish or an amphibian . . . become conspicuous, and there is a pronounced tail.” The face becomes “reptilian. . . (then) somewhat pig-like.” Eventually, it “resembles a primate’s but is still not quite human.”

[Quotes mined from Carl Sagan and Ann Druyan, “Is It Possible To Be Pro-Life And Pro-Choice?” Parade Magazine, April 22, 1990, pp. 5-7.]

Before I start taking apart Humber’s poorly-constructed argument (beware short quotes with many … in them), it should be noted that evolutionary science does not survive or become extinct by the words of Carl Sagan. Carl Sagan was a great communicator of science, that is beyond reproach, but as often as he mentioned evolution it was not his chosen field, and even if it was an incorrect illustration here or there would not debase all of evolutionary science. Darwin was wrong about how animals inherit traits, Galileo thought Saturn had one sun on touching either side of it, and Henry Fairfield Osborn confused the tooth of a pig for a hominid, but science did not screech to a grinding halt because of any of these mistakes (nor for the many others that have been made through the centuries). In fact, the scientific process feeds on mistakes and falsifying hypotheses; if no one was ever wrong about anything science would utterly break down, turning into political debate more than educated discourse. Therefore, even if Carl Sagan was wrong in his 1990 article (or in other works where he discusses development) it would not nullify evolutionary science; a mistake made by a high profile scienctist does not equal a mistake that eliminates that science.

In this case, however, I have the advantage of letting Sagan defend himself. In Billions and Billions, this footnote is included in the discussion about development and abortion;

A number of right-wing and Christian fundamentalist publications have criticized this argument [that a 3-week-old embryo looks like a segmented worm]-on the grounds that it is based on an obsolete doctrine, called recapitulation, of a nineteenth-century German biologist. Ernst Haeckel proposed that the steps in the individual embryonic development of an animal retrace (or “recapitulate”) the stages of evolutionary development of its ancestors. Recapitulation has been exhaustively and skeptically treated by the evolutionary biologist Stephen Jay Gould (in his book Ontogeny and Phylogeny [Cambridge, Mass: Harvard University Press, 1977]). But our article offered not a word about recapitulation, as the reader of this chapter may judge. The comparisons of the human fetus with other (adult) animals is based on the appearance of the fetus (see illustrations). Its nonhuman form, and nothing about its evolutionary history, is the key to the argument of these pages.

Unfortunately I do not have access to the Parade article in question (I know that’s where I go for my scientific information…) Fortunately, the Parade article in question was reproduced in Billions and Billions, and so even though I missed the magazine I can still see what all the fuss was about. Indeed, Sagan does not mention nor endorse recapitulation in his discourse on human development, but he does relate the appearance of the fetus to various adult animals (as noted in his quote). At various stages the fetus does look similar to a worm or a fish or a pig, but merely mentioning these observations doesn’t automatically mean allegiance to Haeckel’s ideas. Is it wise, however, to use such descriptions, so similar to what was related in the recapitulation argument? I don’t think so, especially because (without qualification or the requisite history about developmental science and evolution) the reader can easily jump to conclusions when an author says that a fetus looks like a worm, then a fish, then a reptile, and then a mammal.

Perhaps there is more to this story than could initially be assumed, however. It would be easy for me to end my discussion here, clear that Sagan arguably chose a poor rhetorical device instead of endorsing an incorrect piece of scientific history, but such would be dishonest. In considering Humber’s charge my mind lept back to Sagan’s Dragons of Eden, and enjoyable (although outdated) book about the evolution of intelligence. In the book Sagan seems to try and find analouges in our brains and behavior that correspond to our evolutionary ancestors, humans carrying a collection of innovations largely donated to us by our ancestors. This may be true to an extent, our own evolution was contingent on the evolution of primates, placental mammals, amniotes, tetrapods, and so on down the line to the last common ancestor, but Sagan does seem to overstep the boundary in his 1977 book. In the chapter “The Brain and the Chariot” Sagan writes;

It is very difficult to evolve by altering the deep fabric of life; any change there is likely to be lethal. But fundamental change can be accomplished by the addition of new systems on top of old ones. This is reminiscent of the doctrine which was called recapitulation by Ernst Haeckel, a nineteenth-century German anatomist, and which has gone through various cycle of of scholarly acceptance and rejection. Haeckel held that in its embryological development, an animal tends to repeat or recapitulate the sequence that its ancestors followed during their evolution. And indeed in human intrauterine development we run through stages very much like fish, reptiles, and nonprimate mammals before we become recognizably human. The fish stage even has gill slits, which are absolutely useless for the embryo who is nourished via the umbilical cord, but a necessity for human embryology: since gills were vital to our ancestors, we run through a gill stage in becoming human.

Sagan goes on to qualify that human embryos have pharyngeal slits not because ancient adult fish had them, but because ancient fish embryos had them and there was no reason to lose them in development. This points towards the modern understanding of recapitulation, that changes in the genome because of mutation can far more readily change recent innovations/developments than ancient ones, or (to employ an example) it would be far easier to increase or decrease the size of our cerebrum than it would be to alter our brain stem or limbic system and survive the consequences. Thinking about it another way, it’s far easier to rearrange the setting of a table than to entirely remove the tablecloth while leaving all the settings in place (although this can be done, and so too is it possible in evolution).

Hence I would be loathe to say that Sagan unequivocally endorsed recapitulation theory in Dragons of Eden; he seems to think there is some merit to the idea, but (like in Billions and Billions) he does not state that we look like a fish at one point in the womb because we are replaying evolution. There are remnants from our evolutionary past in development, that is sure, but embryos do not undergo a “replaying of the tape” during their nine months in the womb, either.

Again, I think Sagan should have stayed away from equating steps of human development to worms, fish, and pigs in his later writings as such conjures up the spectre of Haeckel, but an attentive reader will realize that he is merely describing his observation of what the embryo resembles rather than stating “It looks like a pig because we evolved from pigs.” Even if he did, would we be so ungracious as to categorize the rest of his work (or the rest of science) as junk? I don’t see anyone claiming that science is defunct because there are still flat-earthers or creationists espousing their views; different players move on and off the stage that is scientific discourse, but in the end it is something that is truly bigger than any one scientist or idea.




One response

13 06 2007
“Make me a cell, darn it!” sez Jim « Laelaps

[…] I Countering Creationism, Pt. II; “Zinj” Countering Creationism, Part III; Tale of a T. rex Countering Creationism, Part IV: Carl Sagan & Development The Dragons of Eden (Creation Museum Carnival Entry) Responding to Bob Painful and Purple Prose: […]

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