Human Cloning and Stem Cells

Of the countless interviews I have conducted with scientists over the years, only once has a question prompted something of a striptease. In December of 1999, I found myself in the elegant parlor of the Union Club in New York City, chatting with a biologist named Leonard Hayflick. Although hardly a household name to the general public, Hayflick is that rare scientist whose name is permanently attached to a biological phenomenon. It is known as the “Hayflick limit,” and it derives from experiments he did in the late 19505 and early 19605 showing that human cells grown in Petri dishes will predictably replicate for a certain number of cell divisions, but then hit a wall and stop dividing. This has obvious implications for cell biology, aging, and immortality (of the in vitro sort), and indeed the Hayflick limit has been the seed around which a spirited biological debate about the biology of aging has swirled, without definitive resolution, for about four decades now. Because of this history, Hayflick has closely followed the recent work on the biology of aging and regenerative medicine, which in turn has made him a front-row spectator in the more recent controversies involving human embryonic stem cell research and “therapeutic cloning.” At the time of my conversation with Hayflick, his longtime friend Michael West was attempting to obtain human embryonic stem cells through cloning—in a particularly controversial way, by putting human cells into egg cells from ... cows. Almost as an aside, I asked Hayflick what he thought about West's experiments. Hayflick replied by rolling up his pants leg. He bared enough skin to be able to point out a tiny dimple on his right knee. “The human cells he's using for the cow work came from here,” he said. I had to stand up and lean over to see it, but there was undeniably a tiny divot in Hayflick's skin. The implications were stunning: Leonard Hayflick, the father of cellular senescence and one of the elder statesmen of gerontology, was allowing himself, in a manner of speaking, to be cloned. In addition to making the obvious point that even the most innocuous question can elicit a startling answer, Hayflick's reply offered another lesson, too: that colorful characters can provide a narrative thread for bringing a controversy to life.