Did Our Ancestors Digest Insects?

Continuing the discussion from Did We Have "Reptilian" Ancestors?:

By way of @pevaquark comes a really interesting article, exploring the broken insect digesting gene in all mammals, chitinase. Chitin (Chitin - Wikipedia) is an insect specific molecule that we cannot currently digest. The

The destruction of chitinase genes shows a nested clade pattern too. I’m curious @pnelson and @Agauger’s thoughts on this. It seems like very strong evidence for common descent.

Original paper here:

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Here is another phenominal paper relevant to this:

Evolutionary relationships as inferred from CHIA sequences, including timing of CHIA pseudogenization events. *The pseudogenizing mutation found in the Miopithecus ogouensis hCHIA sequence is the same as the one found in the Papionini (Macaca spp., Papio spp, etc.), but is not found in the other Cercopithecini. It is unclear what accounts for this unexpected pattern, but possible explanations include ancestral polymorphism or ancient hybridization.v
Evolutionary relationships as inferred from CHIA sequences, including timing of CHIA pseudogenization events. *The pseudogenizing mutation found in the Miopithecus ogouensis hCHIA sequence is the same as the one found in the Papionini (Macaca spp., Papio spp, etc.), but is not found in the other Cercopithecini. It is unclear what accounts for this unexpected pattern, but possible explanations include ancestral polymorphism or ancient hybridization.

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Fascinating! I wonder if anyone has compiled a website with a title like “The Catalog of Broken Genes.” Even as someone with limited knowledge of evolutionary biology and genomics, I can think of quite a few “broken genes” in an ever growing list which constitute powerful evidence for Common Descent.


SIDE NOTE: As a has-been linguist, I am often impressed at how effectively scientists have used mnemonic morphemes in their terminology since the dawn of modern science. For example, in Joshua’s post he referred to chitinase. Now I had never seen that term before—but because it combines descriptive morphemes, I instantly knew that chitinase must be an enzyme (due to the -ase suffix) which digests/degrades/breaks-down the chitin which is important to arthropod exoskeletons as well as fungi structures. It is also worth noting that chitin is a polysaccharide, where the Greek morpheme poly means “many” and saccharide is from the Greek word for sugar. So a polysaccharide is a molecule consisting of many sugars (typically glucose, though other simple sugars are also possible, if I recall correctly.) Even without any training in biochemistry, I would instantly have a good idea what the term polysaccharide describes.

I think science education, even at the middle-school level, would be greatly aided by one-credit hour courses on Greek and Latin morphemes. Even learning just a few hundred morphemes would go a very long way. This would greatly aid reading comprehension, not only in science but in philosophy, art, mathematics, political science, and many other fields of the humanities.

It always saddens me when I hear politicians, journalists, comedians, and even some Christian apologists who should know better deriding scientists for “speaking jargon”, as if the technical terminology is meant to confuse or obscure. In reality, I’m often favorably impressed at how the technical terms coined by scientists are remarkably effective at communicating meanings. Chitinase is just the latest example which I could cite.

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Three quibbles:

  1. There are five mammalian chitinase genes, not 1.
  2. They aren’t broken in all mammals. In some, all 5 are intact. In others, fewer. In still others, none.
  3. Chitin isn’t insect-specific. It’s present in all arthropods, and in some lophotrochozoans.
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So you disagree with the author’s conclusion?

Not at all. Great article. It didn’t say any of those things, though.

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Chris Emerling’s blog has lots of other great articles along these same lines, e.g.

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Notice, by the way, that the baleen whales in that article have chitinase pseudogenes despite their diets of crustaceans. Pseudogenization tracks phylogeny better than it tracks current habits.

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Do crustaceans have chitin? Turns out they do. Insects of the sea it seems.

Actually, insects are crustaceans of the land. Crustacea, in other words, is paraphyletic to Hexapoda.

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