"The goal is to answer the basic question: What makes us humans?" said Eichler.
Eichler and his colleagues found that the human and chimp sequences differ by only 1.2 percent in terms of single-nucleotide changes to the genetic code.
But 2.7 percent of the genetic difference between humans and chimps are duplications, in which segments of genetic code are copied many times in the genome.
"If genetic code is a book, what we found is that entire pages of the book duplicated in one species but not the other," said Eichler. "This gives us some insight into the genetic diversity that's going on between chimp and human and identifies regions that contain genes that have undergone very rapid genomic changes."
Humans and chimps originate from a common ancestor, and scientists believe they diverged some six million years ago.
Given this relatively short time since the split, it's likely that a few important mutations are responsible for the differences between the two species, according to Wen-Hsiung Li, a molecular evolutionist at the University of Chicago in Illinois.
"If you look at two species of frogs over 10 million years, you probably won't see a lot of the morphological or behavioral differences that you see between humans and chimps," said Li, who wrote an accompanying commentary on the chimp genome sequencing for Nature.
There are several hypotheses that account for the evolution of human traits. Li believes these traits come from changes in the parts of the genome that regulate other gene activity.
Scientists agree that many questions remain unanswered but the chimp genome provides important clues to understanding what makes us human.
"We're in a very nice intermediate stage of understanding human-chimp differences," said Eichler. "We can't say, This is the difference that makes us human, but we can say, These are the regions of the genome that show a lot of potential and are excellent candidates to do further work on."
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