The natural world is rife with leftovers. Over the course of evolution, body parts that no longer benefit their owners eventually waste, away leaving behind shrivelled and useless anatomical remnants. The human tailbone is one such example. Others include the sightless eyes of cavefish that live in total darkness, the tiny spurs on boas and pythons that hint at the legs of their ancestors, and the withered wings of the Galapagos cormorant, an animal that dispensed with flight on an island bereft of land predators.
Animal genomes contain similar remains. Just like organs, genes also waste away if they stop being useful. They accumulate crippling mutations that kill their ability to make proteins and turn them into functionless “pseudogenes“. They have no useful role other than to tell inquisitive geneticists about their histories.
So organs can degenerate and genes can decay. The two processes should clearly run in parallel, but there are few documented examples of this. Robert Meredith from the University of California Riverside, has uncovered just such an example, a beautiful case study where the decay of a gene called enamelin clearly parallels the loss of a body part – tooth enamel.
Enamel is an extremely tough material that coats the outside of our teeth. Many proteins are essential for making it, including the aptly named enamelin, which is produced by a gene of the same name. Meredith’s team sequenced the enamelin gene (ENAM) in 20 species of mammals that either have teeth without enamel caps (like aardvarks, sloths and armadillos) or that lack teeth altogether (like anteaters, pangolins and several whales).
Today, every single one of these species has a broken version of enamelin. Mutations have crept into these genes, which stop the production of the protein before it’s fully formed. The result is a busted gene that produces a runty, useless protein. Other mammals don’t suffer from this problem; Meredith found that ENAM is fully functional in 29 other toothed mammals, including cats, cows and dolphins.
This is exactly what you’d expect, but the clear link between the lack of enamel and a broken enamel-producing gene is exciting nonetheless. It’s a tale that, in Meredith’s own words, provides “manifest evidence for the predictive power of Darwin’s theory”.
On the fifth day of this year, I found myself sitting in the living room of the legendary Sir David Attenborough, drinking coffee and talking to him about wildlife, filmmaking and his career for the better part of an hour. It was a truly memorable experience, not just for his eloquence and storytelling skills, but because Sir David has been a hero of mine since I first popped Life on Earth into my VCR at the wee age of 8. His clarity and passion have inspired me to become a better communicator of science and it was a privilege to speak to the man in person.
He was no less of a superb raconteur in the flesh than he is on screen, and incredibly down-to-earth regarding his fame and status. His house was beautiful, furnsihed by the expected paintings of wildlife and tribal artifacts, a collection of beautiful fossils on a shelf behind his sofa, and more incongruously, an absolutely massive plasma-screen telly.
So now, as 2008 comes to close, I felt it fitting to repost the interview that began the year on such a high. It’s long, but Attenborough has so much that’s worth listening to. I hope you enjoy it as much as I did.