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.
Recently, Detlev Arendt, a biologist at the European Molecular Biology Laboratory, and his colleagues investigated the evolution of an important but overlooked feature in our bodies, known as the notochord. It’s a stiff rod of cartilage that develops in human embryos, running down their back. Later, as the spine develops, the notochord transforms into the disks that cushion the vertebrae (and sometimes slip later in life, causing much grief).
Arendt and his colleagues wondered how the notochord first evolved. Squid don’t have a notochord. Neither do clams, or cockroaches, or tarantulas. The notochord, in other words, seems to be unique to chordates. So where did it come from? Did it emerge right at the dawn of chordates, or did it have deeper origins?
Read the full, original story: What slipped disks tell us about 700 million Years of Evolution
