Lizards, Birds Have Hair Genes
for National Geographic News
|November 10, 2008|
Our hair is rooted in reptilian claws, according to a new study that revealed hair genes in both lizards and birds.
Previously, scientists thought hair first appeared in mammals.
Hair, which provides insulation and protection, is seen as one of the main evolutionary innovations that led to the rise of mammals.
But the origins of hair date back to an unknown reptile ancestor that lived more than 300 million years ago, in the Paleozoic era, the new study says.
(Explore geologic time.)
A team led by Leopold Eckhart of the Medical University of Vienna in Austria made the discovery by comparing human, chicken, and green anole lizard genomes.
The genome of the lizard was found to contain six different genes for hair keratin, the protein from which mammal hair is made.
The genes were expressed most strongly in the lizard's toes, indicating that the first hair genes played a role in claw formation, the study team reports in tomorrow's issue of the Proceedings of the National Academy of Sciences.
"At least two of these hair protein keratins are formed in the growth zones of the claws," Eckhart said.
While the role of the anole lizard's four other hair genes remains unclear, they were likely related to the growth of scales, the study team said.
The chicken genome revealed a single hair gene. It's unclear what that gene is for, if anything.
The finding suggests that modern birds, reptiles, and mammals—as well as dinosaurs—shared an early common ancestor that had claws built from hair keratin, Eckhart said.
"Actually, it may be more appropriate to call these proteins claw keratins, which later acquired an additional role in hair," he said.
(Related: "New Dinosaur Discovered: T. Rex Cousin Had Feathers" [October 6, 2004].)
Eckhart speculates that hair evolution began with claw keratins that were later adapted to form scales, from which the earliest hairs then developed.
The very first whiskery hairs may even have sprouted on reptiles, Eckhart said.
"However, I don't think it very likely," he added.
"If they were present, I wonder why modern reptiles don't have them any more. If hairs were useful, they wouldn't have lost them."
Günter Wagner, a professor of evolutionary biology at Yale University, said the new study shows that that hair growth wasn't just a matter of having keratin genes.
Only in mammals, however, did keratin evolve into strands.
"The standard theory was that you get hair when you get the hair-specific keratin, but the problem was [actually] how to pack those keratins into very long and thin structures," Wagner said.
Similarly, he said, a recent study showed that birds shared feather-making keratins with an ancient, featherless ancestor of crocodiles.
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