Mastering our own evolution

They couldn’t find one.

So they decided to make one. If they had another baby, the Nashes reasoned, one with an ideal genetic makeup, they could harvest stem cells from the umbilical cord and restore Molly’s ability to make healthy blood.

Doctors harvested some of Lisa’s eggs and fertilized them with her husband’s sperm. They grew the resulting embryos for three days, plucked a cell from each, and screened those cells both for Molly’s disease and their transplantability.

Four times they installed a promising embryo inside Lisa’s uterus. Four times she failed to get pregnant. But on the fifth try, the implantation worked.

Nine months later, Lisa gave birth to a healthy son, Adam. The stem cells from Adam’s umbilical cord saved Molly’s life.

Ten years after Adam’s birth, preimplantation genetic diagnosis is performed regularly, primarily to make sure embryos are missing the gene variants that cause debilitating diseases like Molly’s.

But the curve of technological change sweeps ever higher. Soon we’re going to be able to screen embryos for a lot more than genetic diseases.

“We are on the verge of an incredible explosion of understanding of the functions of different forms of genes,” declares Steven Potter, a researcher at the Children’s Hospital Medical Center in Cincinnati, in his succinct new book “Designer Genes.’’

What will it mean for the future of our species, Potter wonders, when parents can look at a whole spreadsheet of genetic probabilities for their embryos? What will it mean when parents select embryos on the basis of, say, looks, or intelligence, or longevity?

“For the first time in the history of the planet,” he concludes, “we now have a species able to control its own evolution.”

It took the Human Genome Project 13 years and more than $3 billion to map the sequences of chemical base pairs in human DNA. Now, says Potter, we can “sequence a person’s DNA in just one week at a cost of about $10,000.” In the not too distant future, we’ll be able to do it in hours, for hundreds of dollars.

Once we have the DNA sequences for millions of people, even slight variations in populations will show through the data. And once we know that certain gene combinations increase the likelihood for a long, healthy life, who isn’t going to want to bequeath that combination to their children?

Other barriers are toppling. Nowadays a woman stimulated with synthetic hormones can produce a few dozen eggs. But someday we may be able collect her skin cells, transform them into stem cells, and convert those into eggs. Once we improve sequencing and cell-transformation technologies, a well-to-do couple hoping to have a child could potentially create tens of thousands of embryos. Screen them all, select the strongest, smartest, prettiest, and — bingo — designer children.

What comes after that, Potter says, with uncharacteristic bluster, will be akin to “a thermonuclear explosion in the evolution of the human species.”

Will our grandchildren live in a world free of genetic disease? Or will they live in a world of high-tech eugenics, in which governments regulate how populations are engineered?

Potter’s book swiftly explores the ramifications of these brave new possibilities. His prose is steady and unadorned and he regularly makes thorny jargon penetrable. “Designer Genes’’ may not become the definitive text on the genetics revolution, but it’s a competent and hair-raising start.

In “Almost Chimpanzee,’’ journalist Jon Cohen approaches the question of what makes us human by looking at chimpanzees.

Previous studies like Jane Goodall’s, says Cohen, focus on ways chimps seem almost human: tool-use, emotions, social structures, and so on. Cohen believes it’s time to emphasize the ways we differ from our evolutionary cousins.

“Chimpanzees are hairier, sleep in trees, and don’t run long distances or swim,” he writes. “They do not dance with each other, paint on walls of caves, naturally live outside Africa, have blue eyes, make jewelry, or store food.” He goes on to elegantly poke holes in the misleading genetic similarities — the famous truism that chimps and humans share 99 percent of our DNA.

Indeed, after a couple hundred pages of Cohen’s wide-ranging book, I began to doubt that we had any similarities to chimpanzees.

At the end of the book, which includes his visits to chimp-whisperers, chimp-defenders, and experts on chimp fertility, Cohen finally visits wild chimpanzees in Uganda’s Kibale National Park. It’s here that the book finds its emotional power. By the end of “Almost Chimpanzee’’ a reader cannot forget that not only are our cousins in danger of being eradicated entirely from the wild, but that we’re the ones eradicating them.

“Humans will determine the fate of chimpanzees,” writes Cohen. “Chimpanzees of course will have no say in the fate of humans. And that may be the single most conspicuous difference between the two species.”

Anthony Doerr is the author, most recently, of a collection of stories titled “Memory Wall.’’ He can be reached at adoerr@cableone.net.