Notes from Muséum national d'Histoire naturelle Part 2: The lure of the eccentric(2012, Nov. 01) (2015.02.2[Mon.])


  Scientists often change the way they think about things. If one line of reasoning hits a roadblock, they explore a different avenue, and may even discard a cherished hypothesis if the need arises. Some hypotheses can only be arrived at by embarking on such an adventure; it’s strange to think of the role adventures play. Take Étienne Geoffroy Saint-Hilaire’s early ideas about the inversion of dorsal and ventral structures in arthropods and vertebrates, which was later found to have actually occurred during the evolutionary process in a basal vertebrate. No matter how far-fetched a theory may be, if it has explanatory power it may end up changing how we view the world. These are the moments in science when people cry out “Eureka!” The thrill of discovery is what makes thought such a seductive calling.

  When I spent some time at the National Museum of Natural History in Paris, I also undertook adventures of this sort in conversation with my host Philippe Janvier, pestering him with fanciful questions—What if these projections were not pectoral fins? Or if this hole was a nostril, not an orbital? He ruled out each possibility in turn, and I acquired a better understanding of paleontology in the process. This kind of directed questioning based on my knowledge of comparative embryology let him become my own best professor and enjoy a wonderful private lesson with a fellow expert.

  During those chats, the conversation would often wander off in strange directions, and Philippe would steer us back on track by calling stop (not quite Catcher in the Rye, but...). He had on his computer a folder of Odd Papers where he kept the various fringe and sometimes lunatic published theories he had come across. (And indeed I have my own shelf of ridiculous books.) Interestingly, several of the odd papers were published in respectable journals. Researchers who pour their blood and tears into trying to get their work accepted may find this hard to believe (I have a hard time believing it myself), but from time to time we see just this sort of crazy talk get published. And it is wonderful that there are sane-minded people in this world who believe such ideas with all their hearts.

  Take the theory of the bipedal evolution of terrestrial animals for example. In parts, it smacks of Haeckel's discredited ideas about recapitulation. But what you may not know is there is a serious theoretical study of those same ideas. The basic proposition is that some ancient sand-dwelling cephalochordate-like organism would inflate its cerebral vesicle and use it as a kind of flotation device. From this it was only a short trip to the human body, as fins became legs and a previously horizontal form turned vertical and emerged onto land. In this line of reasoning, our heads are in fact only repurposed buoys. Quadrupeds came along later, and so humans are part of the most ancestral lineage of terrestrial animals. I think I read a science fiction novel with the same basic theme once...

  Next, let's have a look at a theory that was actually partially published in a major journal, with scandal ensuing. The idea tries to explain the origins of larval stages found in many animal species. Amphibian and ascidian tadpoles are well known, as are lepidopteran caterpillars. The larval stage in such animals is completely different from the adult, but where does it come from? It is generally accepted that the frog tadpole is a secondarily acquired developmental stage, but its origins remain a real enigma.

  Anyway, in the article in question, the authors proposed that larvae are the products of crossbreeding between species. Cross a larva-less lamprey with an amphioxus and you introduce the ammocoete into lamprey development. Similarly, the tdapoles of modern frogs represent a developmental hybrid between their amphibian ancestors and a now-extinct agnathan.

  It has to be admitted that ammocoetes resemble amphioxis. Both live in the mud and filter feed, for which they are equipped with a secretory gland called an endostyle. Both have sarcomeres all along the body axis, but these originate from different primordia and there is little correspondence between the two at the anatomical or developmental level. The similarities between the amphibian tadpole and cyclostome larvae, however, are more interesting. The mouthparts show an eerie homology (see Fig.), and in my own studies I have seen that this has its basis in their respective embryos.

  I mean, there still remains a dangerous temptation that makes you say, 'I wouldn't simply forget it since I see a bit of truth in there'. But this is no more than an overdue evolutionary theory. Patten, Gaskell, and Dohrn were all eminent zoologists, but in retrospect they all had their share of wild notions. But the problem is more fundamental. We can reject 99% of the cryptozoology and UFOlogy out of hand, but what of that last 1%? I wouldn't be so quick to dismiss it. That doesn't mean I believe it of course. For such novel ideas to be true would require the overturning of huge amounts of previous work and the introduction of many new working hypotheses to explain the inexplicable.

  There is no place for faith in science; doubt has more rewards. But that is not to say that scientists aren't consumed with their own beliefs—they are true believers in the Church of Commonsense, although admittedly with a strong creative streak and, ironically, a solid work ethic. However you look at it, pursuing research is uncomfortably close to chasing illusions, and a big gray zone spans the gap between science-mindedness and religiosity. Sometimes the joy of discovery brings a ray of light to that space. Whether it be enlightenment or self-deception, that for me is the essence of insight.