In 2001, scientists announced they'd mapped the human genome—the string of genetic instructions woven into our DNA. That map has led scientists to buried treasures of understanding.

Now the same thing has happened for the chimp genome. The Chimpanzee Sequencing and Analysis Consortium, a huge international scientist cooperative, announced the sequence in the Sept. 1 issue of Nature. So we're about to know our closest cousins better.

And ourselves. This new map may help us answer one of the biggest of all questions: What makes us human?

Help us answer, mind you—not answer everything. Keep that in mind.

The common chimpanzee (Pan troglodytes) is our closest living evolutionary relative. Both Pan and Homo (our genus) are branches from a common ancestor, from which the two lines went different ways about 6 to 8 million years ago. Chimps have changed since then—and so have we, in spectacular fashion. The chimp genome now gives us a point of comparison. It's close: Between 95 and 98.5 percent of our genetic strings are identical.

True, that figure can be misleading. It's not the percent difference or the number of genes that counts—it's the specific genes that are different, the way they interact, and the differences they make. But within that 1.5 to 5 percent, we can narrow our search for the changes that kick-started humanity. Romancing those nuances will engross scientists for many years to come.

So many questions, so many mysteries about us: They're very hairy; we're not. They grow up fast; we retain adolescent traits into adulthood. Why are we so bipedal? Our brains are about three times the size of a chimp's—a huge difference that happened, it seems, pretty rapidly. Why did it happen for us and not Bonzo? Some scientists believe our capacity for language and symbolic thinking may be less than 250,000 years old—relatively recent evolutionarily. OK, so why did it happen?

The guess right now: A small number of mutations, having a huge effect, were responsible for the biggest changes. Our humanity resides in a few glistening gems of change. But that's only a guess.

So this new map will help us understand the origin of the functional differences that make us human and not chimp. But what of the human soul? Is what we call the soul a shard of the divine injected by God into us as we developed? Or is it simply the sum total of our subjective lives?

Science can't be the judge of that. For that, we must go to our churches, our poets, our thinkers, our friends, our own hearts. It's our capacity to embark on that kind of search that makes us most human.