Ever since Richard Leakey and Roger Lewin published The Sixth Extinction in 1995, we have known that humanity is extirpating species at a rate unmatched since the demise of the dinosaurs 65 million years ago. Hunting, deforestation, the introduction of nonnative organisms and diseases, and now climate change have increased the rate of species loss to the point that scientists fear for the functioning of entire ecosystems, and even the stability of the earth’s self-regulatory mechanisms. Until recently it seemed that once a species went extinct, there was little we could do. Extinction truly was forever. But recent developments in genetics have given researchers some hope that extinct species might be brought back to life.

Extinction, of course, involves more than a loss of genes. The cellular environment in which the nuclear genes operate is also lost when a species goes extinct, as are learned behaviors, which can be vital for survival. Undaunted by the formidable complexity of the task, small groups of researchers are working on various aspects of the science increasingly known as de-extinction, and many remarkable advances have been made. In March 2013, for example, a group of Australian scientists funded through a philanthropic donation, and collaborating on what they called “The Lazarus Project,” announced that they had brought a long-extinct species back to life.1

Australia’s southern gastric brooding frog was a very distinctive amphibian that had a unique method of reproduction: the female swallowed her eggs shortly after they were laid, somehow transforming her stomach from an organ of digestion into a brood chamber. Months later, fully formed froglets would leap from their mother’s mouth. Medical researchers hoped that the species’ ability to transform its stomach might hold the key to curing various digestive ailments. But just eleven years after it was discovered, and before medical researchers could study it, the southern gastric brooding frog became extinct.

Between 1982 and 2013 no living individuals existed. But then, for three days early in 2013, the species was again counted among the living. The body of a gastric brooding frog had been kept in a deep freeze at an Australian university. Cell nuclei were taken from the frozen corpse and placed in eggs from one of its living relatives, the great barred frog, from which the original nuclei had been removed. The eggs transformed into embryos, and grew for three days before dying. The leader of the project team, the paleontologist Mike Archer, proclaimed that “we are watching Lazarus arise from the dead, step by exciting step.”2

This is not a new approach. Researchers first successfully transferred a nucleus into a denucleated frog’s egg in 1952, and it’s been known since that…