There ain’t no flies in us.

So I am reading Neil Shubin’s Your Inner Fish, which as noted I was eagerly anticipating. My immediate reaction is that it will be a good little book for non-experts, but the very basic overview of topics and stilted writing style (think of the exact opposite of Stephen Jay Gould’s long, comma-filled, complex sentence constructions) will be less engaging to biologist readers. I suspect that I do not reflect the target audience, though, so no major complaint here.

The title of the book refers to species such as Tiktaalik roseae (which Dr. Shubin and his colleagues discovered, to much deserved acclaim), an extinct species that, in retrospect, held characteristics that we may consider transitional between fishes and terrestrial tetrapods. Whereas Tiktaalik itself is probably not a direct ancestor of ours, I don’t have much of a problem with the “inner fish” idea on the basis of this comparison. After all, we’re talking about extinct ancestors (or things similar to ancestors) that were fishes and from whom we have inherited some persistent characteristics despite the many changes that have occurred in our lineage.

But then on p. 59, in a discussion of developmental regulatory genes which are similar in sequence and effect in different model organisms, we find:

An “inner fly” helped find an “inner chicken”, which ultimately helped Randy [Dahn, one of Shubin’s students] find an “inner skate”. The connections among living creatures run deep.

Here is a phylogeny of the organisms being discussed, all of them modern species:

At no time was there a fly in vertebrate ancestry. There was no skate in the ancestry of terrestrial vertebrates. The ancestral amniote was not a chicken. (And, while we’re on the subject, the ancestor of humans was not a chimp). There is a common ancestor shared by all of these contemporary animals, but it was not a fly any more than it was a human. Humans do not have inner flies — and equally, flies do not have inner humans. If anything, both have an “inner-common-ancestor-of-metazoans”, but admittedly that is more accurate than it is memorable.

4 thoughts on “There ain’t no flies in us.

  1. Good point. “Inner fish” metaphor might be appropriate, since humans are technically “fish” (sensu: guppies + sharks > tunicates). But “inner fly” might as well be “inner redwood.” Haven’t read the book yet, but I’m always interested to hear what other Neils have to say.

  2. How about “inner worm” for all triploblastic metazoans? The MRCA of the triploblasts was probably worm-like, right?

  3. Well, “worm” is a vague term applied to several groups, but if someone said “inner worm” in regards to a modern species of worm (e.g., a nematode or annelid), then this would be incorrect.

    The main point is that you cannot take a modern species from one group and talk about it as though it were the ancestor of another modern species.
    Especially when nothing even remotely like the species in question was an ancestor of the other species under discussion.

  4. “Striving to be man, the worm Mounts through all the spires of form.” -Emerson (Not Darwin!)

    I don’t think Shubin means to suggest that we literally evolved through a fly phase. I’m sure he knows better even if his wording was unclear. I think he means to suggest that we have an “inner fly” to the extent that we share homologous features (and DNA sequence)with flies. In this sense, there is a part of you that is identical a fly. Or maybe Shubin is a closet transcendentalist who believes in the Aristotelian great chain of being. I’m giving him the benefit of the doubt.

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