How Your Hand Evolved: Modern Genetics Reveal Link Between Fins and Hands

Paleontologists may have documented the ancient relationship between fins and hands. Paleontologists have found the origins of the evolutionary adaptations necessary for ancient lobe-finned fish to transform pectoral fins used underwater into strong, bony structures, such as hands.

"Fossils show that the wrist and digits clearly have an aquatic origin," said Neil Shubin, one of the researchers, in a news release. "But fins and limbs have different purposes. They have evolved in different directions since they diverged. We wanted to explore, and better understand, their connections by adding genetic and molecular data to what we already know from the fossil record."

In this case, the researchers examined the genetics underlying the link based on shape comparisons of fin and limb bones. Yet first attempts were largely unsuccessful; the wrist is composed of a series of small nodular bones, followed by longer thin bones that make up the digits. The bones of living fish fins look much different, however, with a set of longer bones ending in small circular bones called radials.

The primary genes that shape these bones are known as HoxD and HoxA clusters; yet these also differ. The scientists tested the ability of genetic "switches" that control HoxD and HoxA genes from teleosts-bony, ray-finned fish-to shape the limbs of developing transgenic mice. The fish control switches, however, didn't trigger any activity in the autopod, which is the modern structure comprising wrists, fingers or ankles and toes.

In the end, the researchers traced the shift between fins and limbs to a radical change in the genetics of teleost fish, more than 300 million years ago, after the fish-like creatures split off from other bony fish. They found that a common ancestor of the teleost lineage went through a whole-genome duplication (WGD), a phenomenon that has occurred multiple times in evolution.

The findings reveal a bit more about the evolution of hands and limbs. This, in turn, gives scientists a better glimpse of evolution in general.

The findings are published in the journal Proceedings of the National Academy of Sciences.

For more great science stories and general news, please visit our sister site, Headlines and Global News (HNGN).