SCI-KIDS: Scientists shake roots of Tree of Life

Tree of Life" is a metaphor for the idea that all life on the planet is related. It conjures a variety of visions.

We see the beauty of a branching tree. Being connected to other life forms evokes personal ties to environmental stewardship for some, and Biblical responsibilities for others.

The mystical roots of "Tree of Life" began to give way to the scientific idea of the connectedness of life in the 1800s.

Charles Darwin sketched a Tree of Life in his "Notebook B," saying, "I think Case must be that one generation then should be as many living as now. To do this & to have many species in same genus (as is) requires extinction. Thus between A & B immense gap of relation. C & B the finest gradation, B & D rather greater distinction. Thus genera would be formed. -- bearing relation to ancient types."

From "Origin of the Species" until fairly recently, the Tree of Life formed a central theme of how life on the planet is connected.

Ancient species divided and branched continuously over time, with some branches dying off (leaving only the fossil record) while other branches survived over time, resulting in the plants and animals we see today.

The Tree of Life concept was a strong suspicion on Darwin's part, without genuine scientific evidence.

Today, however, DNA testing documents the relatedness of plants and animals, and helps determine the order of branching, and how closely related individual organisms are.

Close cousins, such as mice and rats, are living twigs at the outer end of a long branch. More distant cousins, such as mice and rabbits, branched at a point closer to the trunk, and further back in time.

Even more distant cousins, such as birds and dinosaurs, branched a very long time ago (and the dinosaur branch died off).

DNA testing, by counting the number of similar genes and base pairs, identifies how close the branching relationship is between any two life forms.

The most modern of laboratory analyses have vindicated Darwin's suspicions about a Tree of Life. Trees of Life have been drawn many times since Darwin's sketch.

The Tree of Life gives us a clear picture of how closely humans are related to other primates, to elephants, and to sponges.

In a surprise to some, and a contradiction to Darwin's suspicions, scientists have found the overall picture more complex than once thought. In addition to genetic material passing from two parents to one child, it also passes horizontally.

Bacteria routinely exchange DNA in an important process called Horizontal Gene Transfer. Our Tree of Life picture still holds considerable validity, and is a valuable metaphor. Our young scientists-to-be, however, can search for a new metaphor for the way all life on the planet is unified.

In Virginia's science Standards of Learning, life process units begin in K.6, 1.4, and 1.5, and begin their focus on the interconnectedness of life in 5.5.