by CARL ZIMMER
From Zimmer and Emlen, Evolution: Making Sense of Life
There’s a unity to life. Sometimes it’s plain to see, but very often it lurks underneath a distraction of differences. And a new study shows that there’s even a hidden unity between our slipped disks and the muscles in a squirming worm.
Scientists call this unity “homology.” The British anatomist Richard Owen coined the term in 1843, sixteen years before Charles Darwin published The Origin of Species. Owen defined homology as “the same organ in different animals under every variety of form and function.” For example, a human arm, a seal flipper, and a bat wing all have the same basic skeletal layout. They consist of a single long bone, a bending joint, two more long bones, a cluster of small bones, and a set of five digits. The size and shape of each bone may differ, but the pattern is the same regardless of how mammals use their limbs–to swim, to fly, or to wield a hammer.
Darwin argued that homology was the result of evolution. The common ancestor of humans, seals, bats, and other mammals had a limb which became stretched and squashed in various contortions. And over the past 150 years, paleontologists have found a wealth of fossils that help document how the tiny paws of Mesozoic mammals diversified into the many forms found in mammals today.
Phenomena:The Loom for more
via 3 Quarks Daily