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The Evolutionary Link Between Fins and Hands

Today’s scientists are continuing the work started by Charles Darwin in the Victorian Age. He was limited to a simple microscope, they have biological tools.

Darwin suggested that there were similarities in the limbs that humans, moles, horses, porpoises, and bats use for everyday utility and movement.

Carl Zimmer’s article in the New York Times, From Fins Into Hands: Scientists Discover a Deep Evolutionary Link, says that “a team of researchers at the University of Chicago reported that our hands share a deep evolutionary connection not only to bat wings or horse hooves, but also to fish fins.”

But, how could a fin that’s ideal for getting around in the water transform into something more suitable for land-based movement?

Zimmer uses the fin of a goldfish and a human hand as an example. Obviously at first glance there does not appear to be any similarity.

A human hand has tissue called endochondral bones which are “bones that develop from cartilage and contain blood vessels.”

Conversely, a goldfish fin has only a “tiny cluster of endochondral bones at the base of its fin” while the remainder of the fin contains a different type of tissue called dermal bone that “does not start out as cartilage and does not contain blood vessels.”

The difference in tissue has caused some head scratching among scientists.

Afterall, fossils show that goldfish and humans “share a common aquatic ancestor with ray-finned fish” called tetrapods who had four limbs, spines, and were eventually able to navigate and breathe on land.

Evolutionary biologist, Dr. Neil H. Shubin, has been comparing the embryos of present day tetrapods (mice) to fish in his lab at the University of Chicago.

The embryos start out the same until one develops fins and the other develops limbs.

When recent technology became available, Dr. Shubin was able to modify the genes in both types of embryos. It was discovered then that fins and limbs follow the same molecular process of development. Fish end up with dermal bones in their fins while tetrapods, humans for example, develop endochondral bones in their hands and feet.

This is helping to solve the mystery around “fish with limb-like fins.”

Now that researchers know that bone tissue starts out the same for different animals they are better able to understand how fins could be transformed into limbs.

Just think, millions of years ago those hands of yours, capable of complex fine motor skills, could have been fins, elegantly slicing through the water.

For additional background on these studies, click here to read another Carl Zimmer article, Turning Fins Into Hands, from Discover Magazine.

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