Evolution quiz

"Tree of Life" concept
by Brent Mishler,
Deep Green Project.
Photos (left to right):
courtesy of WHOI
- D. Anderson lab
and The Harmful
P. Rogers Sweets
and the Diatom
Home Page; Chimps
Incorporated.

Tree of life, 1999 edition.
We've said it again and again: Molecular similarities on DNA, the genetic memory molecule, indicate a common heritage. Since chimps and humans share about 99 percent of their DNA, we know we shared an ancestor in the fairly recent past.

Delving much further back in time, molecular evolutionists have constructed the new tree of life seen here.

The ongoing reanalysis of genetic lineages stems from the observation of German entomologist Willi Hennig. In the 1960s, Hennig argued that life should be classified not by overall similarities among organisms, but rather by "homologies," or similarities among specific structures.

Homologies, notes Brent Mishler, a professor of integrative biology at the University of California at Berkeley, can arise in anatomical structures, such as the three-part body of the insect, or in the "lettering" of the genetic code. The goal of using homologies is to classify organisms by their family trees -- so all members of a group share a common ancestor in the relatively recent past. (Here's another take on new evolutionary trees.)

Spineless critters
The overall-similarity method, in contrast, produced general groups whose members did not necessarily share a common ancestor. Most notorious was the squishy category "invertebrates," including jellyfish, insects, clams and spiders -- whose only resemblance was their very spinelessness.

Mishler, who helped lead a revision of the evolutionary relationship among green plants, called Deep Green, says the first flowering plant resembled Arborella, a genus of small, cream-colored plants from the South Pacific (see "Rearranging the Branches on..." in the bibliography).

Once molecular techniques became available for detailed examination of tiny specimens, analysis by homologies began revolutionizing the classification of life, says Mishler. Some categories, like insects, still make sense, he adds, but others, like reptiles, have been ditched as based on general resemblances rather than descent from a common ancestor. While the "reptiles" lizards and crocodiles look alike, Mishler says their similarities are "primitive, and not indicative of a recent common ancestor."

The use of molecular techniques has lead to "a total revolution" in classification, says Goodenough. "This has completely replaced Linnaeus (the founder of modern species classification). It's huge."

Beyond indicating who's related to whom, molecular techniques have provided yet another foundation for believing in evolution through natural selection, Goodenough says. "The robust conclusion of all of this is that organisms evolved from each other."

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©1999, University of Wisconsin, Board of Regents.