Humans And Acorn Worms Have Common Ancestry

Posted: Nov 20 2015, 5:02am CST | by , Updated: Nov 20 2015, 10:21pm CST, in Latest Science News


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Humans and Acorn Worms have Common Ancestry
The acorn worm Saccoglossus kowalevskii is common in brackish, shallow water on the Atlantic coast. Its newly sequenced genome is telling biologists about the genes responsible for pharyngeal gills in the hemichordates and chordate structures such as the pharynx, which in humans includes the jaws, tongue, voicebox and various glands and muscles between the mouth and throat. Credit: Chris Lowe, Stanford University

Acorn worms were found to share 70 percent of their genetic makeup with the human beings making them the long lost cousin of humans.

A research group including scientists from UC Berkeley; the Okinawa Institute of Science and Technology Graduate University in Onna, Okinawa, Japan; Stanford University's Hopkins Marine Station; the Baylor College of Medicine in Texas and the United Kingdom have recently published their findings in the Nov. 19 issue of the journal Nature.

Rokhsar, who heads OIST's Molecular Genetics Unit as a visiting professor, and Nori Satoh, head of OIST's Marine Genomics Unit, led the project in which they found the newly sequenced genomes of two marine worms shedding light on the 570 million-year evolution of gills into the pharynx that today gives humans the ability to bite, chew, swallow and speak.

The genome sequence revealed that two species of acorn worm, are the first genomes of hemichordates. That means that they retain similarities to the first animals to evolve pharyngeal or "gill" slits.

The common ancestry eventually gave rise to chordates: animals with backbones and hollow nerve cords, like humans and other vertebrates. The project implies that acorn worms and the human lineage diverged 570 million years ago.

The pharyngeal slits for filtering food evolved into gills for extracting oxygen, and later into today's human upper and lower jaw and pharynx, which encompasses the thyroid gland, tongue, larynx (voice box) and various glands and muscles between the mouth and the throat.

"The presence of these slits in acorn worms and vertebrates tells us that our last common ancestor also had them, and was likely a filter feeder like acorn worms today," said Daniel Rokhsar, one of the leaders of the sequencing effort and a UC Berkeley professor of molecular and cell biology and of physics. "Acorn worms are marine invertebrates that, despite their decidedly non-vertebrate form, are nevertheless among our closest invertebrate relatives."

"It's an ugly beast," acknowledged John Gerhart, senior author of the report and a professor of the graduate school at UC Berkeley. "Acorn worms look very different from chordates, which makes it especially surprising that they and chordates, like humans, are so similar on the genomic, developmental and cell biological levels."

They live in U-shaped burrows in shallow, brackish water on the ocean floor. They swallow sand full of microorganisms and decaying organic matter to get their nutrients, and then let out long "casings," also known as poop, into the ocean.

The common ancestor of today's slimy marine worms shared some 70 percent of human genes which is a huge thing. Our closest biological cousins, the chimps share 98 percent of our genome. 30 percent leaves a lot of room for evolutionary explanations but the similarities have brought us closer to understanding of the development of human biology.

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