Humans Have Primordial Gene That Helped First Mammal Eat Bugs, Scientists Find

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Ladybug on a stem with water drops
Ladybug: We have the fossil gene that, in our ancestors, could have digested the shell of this pretty insect.Credit: Sven Hoppe/AP
Ruth Schuster
Ruth Schuster
Ruth Schuster
Ruth Schuster

Humans possess a primordial gene in their DNA that originated in the ancestor of all mammals, helping the small rat-like animal digest and draw nutrients from the insects it ate, researchers reported in Science Advances on Wednesday. To this day we are among the few higher species blessed with an active copy of the gene, which helps us enjoy and digest insects to this day.

The new genomic study of 107 mammalian species extant today shows that all have the CHIA gene, in one of five forms. The gene codes for an enzyme necessary to degrade chitin, which makes up the hard external shell of insects.

Placental mammals from primates to dolphins and rhinos have the primordial gene, though it isn't active in many. Ergo, we all had to have inherited this gene from a common ancestor, deduce researchers at Montpellier’s Institute of Evolutionary Sciences and University of California, Berkeley.

This primordial mammalian ancestor, a rat-like being that lived over 100 million years ago when dinosaurs were running riot, was insectivorous, they conclude: it ate and could digest insects, with this gene being responsible for digesting the chitin exoskeleton. We can assume this because the species arising from that ancestor all have CHIA genes, explain the scientists.

Also, we can assume that since the mother of all mammals looked like a rat and was about the size of one, it wasn't hunting velociraptors. But it could have dined on plants. And maybe it did scavenge dead dinosaurs and flossed its fangs with plant fibers too, but what it definitely ate was insects.

Over the eons, the CHIA gene gradually became inactive in the mammals that moved onto eating other creatures. "Mammals gradually abandoned an insectivorous diet after the disappearance of the dinosaurs," write the scientists.

In animals today, insect-eating species have active CHIA genes and can digest the whole insect, shell included, just fine. In others the ability ranges.

Among the primates, smaller monkeys that eat insects have more active copies of the CHIA gene; some monkeys have none; the tarsius, uniquely, has five; and we have one, a separate paper, in Molecular Biology and Evolution, reported in March.

In a warming world, insects are likely to proliferate even more than they already do, while cows and sheep and other animals that people like to eat are likely to suffer. Maybe in the future we may wish to resort to genetic engineering not to clone our dog. but to reactivate that useful primordial gene.