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How swimming fish evolved into land-traveling, four-limbed vertebrates is a longstanding mystery.

Twelve years ago,��of the University of Chicago unearthed a 370-million-year-old����that was hailed as a “missing link” from sea to land animals.

But how, exactly, can a fin turn into a limb?

This week in��,��Shubin and colleagues report on work initiated at the Marine Biological Laboratory (��Ůֱ������) that provides major insight into the game-changing fin-to-limb transition. Led by Tetsuya Nakamura, the team showed that a set of genes, called��Hox,��plays a surprisingly similar role in patterning the rays of fins and the digits of tetrapod limbs.����calls it the discovery of�� “a deep evolutionary connection” between fins and hands and feet.

This work was launched in the ��Ůֱ������’s��Whitman Center��in 2014, when Nakamura began studying the role of��Hox��genes in embryonic skates and sharks. With subsequent training in gene editing (CRISPr–Cas9) at the��National Xenopus Resource��at ��Ůֱ������, Nakamura created zebrafish mutants to further study��Hox.

“This extraordinary study highlights the scientific convening power of the MBLand provides an elegant example of the unique opportunities the laboratory continues to provide to young scientists to take risks and drive forward major questions in biology,” says MBLDirector of Research Jonathan Gitlin.