Remember the lamprey larvae that — when some researchers looked into it — turned out to be nothing like they were supposed to and knocked the textbook vertebrate history for a loop? Here are some thoughts from the paper’s first author:
This Haeckelian view has held its status as conventional wisdom for 150 years, around for as long as Victorian novels. Ammocoetes, and by extension lampreys as a whole, have been treated and presented as “swimming time capsules” (as quoted in a media interview with my coauthor Michael Coates) in literature and classrooms. Sure, experts always had a healthy dose of skepticism and varied in their versions of the story. Amphioxus are now relegated to the earliest branching chordate lineage, no longer a cherished sister group to vertebrates. Stem vertebrate fossils from Cambrian times do not exactly appear ammocoete-like in their anatomy. Hagfish –– the other living jawless vertebrate lineage –– develop straight from embryos without any distinct larval phase. And we cannot forget a prophetic review of ammocoete origin hypotheses by Thomas Evans, Philippe Janvier, and Margaret Docker.
Nevertheless, we continue to depict a vertebrate ancestor that looks like nothing but an ammocoete. This is somewhat akin to the treatment of chondrichthyans (sharks, rays, skates, and chimaeras) in vertebrate zoology. Despite unequivocal fossil evidence to the contrary, the classical narrative persists, which views the serially patterned developmental anatomy of elasmobranchs as the paragon of vertebrate archetype. Similarly, the Ammocoete-First (or Ammocoete-Primitive) story is just so convenient that it has infiltrated our way of thinking about vertebrate origins irreplaceably.
Once fortified with historical inertia, just-so stories are difficult to interrogate.
Tetsuto Miyashita, “Agnatha All Along? Changing the Evolutionary Narrative of Vertebrate Origins” at Nature Ecology and Evolution Community
Just-So stories in science are not just difficult to interrogate but risky! People fear the questioner Doubts the Narrative and That Is Not Allowed.
The essay is charming and it is heartening to read someone in science who is prepared to let evidence, not Narrative, be the guide.
The paper is closed access.
See also: Researchers: Lamprey larvae do NOT resemble the early animal “that all vertebrates evolved from” The resemblance sounds like so nice and neat a Darwinian belief that few can have wanted, in these times, to subject it to scrutiny. But some people did. And it’s almost like they don’t mind rewriting the textbooks. It’s as if they don’t “trust science” or something.