BYU Today

Assembling the “Tree of Life”


There is a growing movement among biologists to devote increasing resources to the ambitious goal of cataloging and organizing all species on Earth into a vast “Tree of Life.” Understanding how seagulls are related to eagles, determining who are the crocodile’s cousins, and finding where koalas come from have countless implications for conservation, medicine, and environmental science.

In a commentary in the Nov. 12 issue of this country’s premier scientific journal, Science, Keith A. Crandall, associate professor of biology, endorses tapping vast computing power to fill in missing branches of the tree before species extinctions make it too late.

Crandall, a population genetics expert, writing with one of his PhD candidates, Jennifer E. Buhay, ’06, advocates the methods of some California researchers who mined various public databases for genetic information about 100,000 species and compared the DNA sequences to determine relationships. Although no complete genomes were included, the group’s computer analysis still yielded a viable outline of the “tree.”

The consequence, say Crandall and Buhay, is that scientists need not spend extensive time and resources defining the “trunk” and “thick branches” of the tree, but instead should seek to gather genetic information from all the “leaves,” or individual species. The trunk and branches can be filled in by computer analysis of the leaves.

“While we are busily trying to figure out these big branches, the leaves are dropping off of the tree in the sense that species are going extinct,” Crandall says. “And we aren’t going to be able to study these leaves if we don’t get out there and figure out what they are right now.”

Simply looking at animals and plants and documenting their physical differences isn’t enough, the researchers say. Only through cataloging and comparing their DNA signatures can relationships be established throughout the entire treeā€”DNA provides the universal character set.

“It’s just amazing our lack of knowledge of species on the planet Earth,” Crandall says. “We spend billions of dollars a year to go to Mars to search for life when we can’t even articulate the life that’s here on our own planet. The estimates range from four million existing species to a hundred million species, and we are losing about 20,000 species a year.”