Human Hair Linked to Lizard and Dinosaur Claws

Nov. 11, 2008 -- The origins of hair date back 310-330 million years ago to the last common ancestor of mammals, birds and lizards, according to a new study that discovered genes associated with hair production in living green anole lizards and chickens.

While lizards and chickens are not hairy, their claws contain proteins nearly identical to those found in the human hair shaft, fingernails and toenails, on the surface of the tongue and within the thymus gland.

Since the last common ancestor of mammals, birds and lizards lived before the first true dinosaurs emerged, both dinosaurs and humans appear to have inherited the genes responsible for human hair and animal claws. In short, the structure of our hair and nails may add to the evidence that we are distantly related to dinosaurs and many other creatures, both extinct and living.

"Our hypothesis is that the common ancestor evolved claw proteins because claws were helpful in climbing," lead author Leopold Eckhart told Discovery News. "Later in evolution, but only in mammals, the same proteins were also produced at other sites of the skin and were used to build hair."

Eckhart, a researcher in the Department of Dermatology at the Medical University of Vienna, and his team built their research upon prior work by the Broad Institute in Boston, which unraveled the complete genome of the green anole lizard, a popular terrarium reptile.

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Comparison of the Broad Institute data with the genomes of humans and chickens -- representing all birds -- allowed Eckhart and his colleagues to identify hair proteins, known as hair keratin, in all three test groups: chicken, lizard and human.

Eckhart explained that the genes responsible for hair keratin production stand out from other genes due to certain unique properties. These characteristics were present in the three seemingly diverse studied animal groups.

The findings are published in this week's Proceedings of the National Academy of Sciences.

"Genes are arranged on chromosomes like pearls on a string," he said. "The arrangement of most genes has not changed during evolution. Mammalian hair keratins and the hair keratins of the lizard are flanked by the same genes."