Axing the Family Tree
Dateline: 07/01/99
Forget what you've read in high school biology books: new evidence suggests that the animal family tree is about to change. By studying genes, scientists have shown that almost all animals fit within a simple, three-limb tree of life.
The researchers studied the Hox genes, which help cells organize into different body parts during development. Three disparate animals were studied: an unsegmented marine worm, a lamp shell, and a segmented worm. Based on the traditional animal family tree, these organisms are seemingly unrelated.
The findings were astounding! Looking at the genes, scientists found support for the three-limb theory. The Hox genes in each of the animals studied were very similar but with small (and significant) differences. Those differences point to a common ancestor that eventually diverged into the three different paths. The genetic analysis suggests that these three branches diverged some 550 million years ago from a common ancestor.
Through anatomical comparison, scientists had previously developed the many offshoots on part of the tree. By comparing the morphological characteristics of different animals, they were able to place them within the family tree. These comparisons suggested many pathways on one of the branches of the tree.
On the other hand, this new molecular comparison strongly suggests that part of the tree can be simplified into one limb yielding the three-limb structure. This common molecular and genetic evidence places almost all animals except sponges and jellyfish, and including humans, in the three limbs. It supports the three-pronged version of the animal family tree that has been advanced in the last several years. Interestingly enough, based on this molecular evidence, similar anatomical characteristics do not necessarily denote a close lineage as was previously thought.
The animal family tree has seen both major and minor revisions over the last decade. Scientists are continually updating and modifying the tree in an attempt to accurately determine the course of evolution.
What do you think? Is this three-limb version of the animal family tree cogent? If not, why? Come over to the Biology Forum and share your thoughts, opinions, and feelings.
For other information see:
Animal Tree
A look at the morphological and molecular based trees of animal relationships.
Evolution Net Links
Links and information pertaining to evolution.
