The experiment was an attempt to turn ordinary cells
obtained from human adults into fully functional gametes—
that is, sperm or egg cells. No one has done it yet, but scientists
say they are on the cusp of proving it is possible. If they can
develop a technology for manufacturing eggs and sperm in the
lab, it could bring an end to the problem of infertility for many.
But it would also present a fundamental and, to some, troubling advance toward reducing the creation of life to a procedure in a laboratory.
It’s part of an explosion of research into how cells make
decisions about their fate. To be a neuron or a beating heart
cell? From the moment an egg is fertilized, a flurry of biochemical signals orchestrate its division, growth, and specialization as a complete new life is formed. The ambition of
biologists who study development is to understand each step
and, if they can, copy it in their laboratories.
And no type of cell made in the laboratory would have a
bigger scientific and social impact than a sperm or an egg. Re-
creating these would give scientists access to the chamber of
secrets where the links between the generations are forged. “Is
there anything more interesting than that? It’s so amazing,”
says Renee Reijo Pera, the scientist who carried out the experi-
ment with B.D.’s cells. “I know people who study how did life
begin on Earth, or work on finding the edges of the universe.
And I think none of that beats the fact that the sperm and the
egg come together and you get a human. And mostly we get
two arms and two legs. It is amazingly accurate.”
Progress toward making “artificial gametes” has been
accelerating. In Japan, mice were born from eggs scientists
had manufactured in a dish from a tail cell. Chinese scien-
tists later claimed they had determined the exact sequence
of molecular signals required to make mouse sperm. So far,
the exact biochemical formula for prompting a stem cell to
mature into functional human eggs or sperm remains out of
reach. No human skin cell has been turned into a bona fide
human reproductive cell. But many scientists believe it’s only
a matter of time—maybe only a year or two—before they get
the right recipe. Recent advances have been “absolutely clear,
and breathtaking” says George Daley, a stem-cell biologist
who recently became dean of Harvard’s medical school.
As control over the fundamental units of reproduction
advances, the work is drawing the attention of entrepreneurs,
legal experts, bioethicists, and specialists in in vitro fertilization.
Some believe that artificial gametes could be the biggest leap
forward since IVF itself was first tried, in 1977. Many millions
of people can’t reproduce, whether because of cancer, accidents,
age, or genetics. “You’d be saying that if you have skin, which
you do if you are even alive, then you can have sperm,” says B.D.
The technology could carry socially disruptive consequences. Women might have children regardless of age. Just
grab some skin and poof, young eggs. And if eggs and sperm
can be produced in the lab, why not also make embryos by the
dozens and test them to pick those with the least disease risk
or the best chance of a high IQ? Henry Greely, a member of
Stanford University’s law faculty and one of the most influential bioethical thinkers in the U.S., finds that scenario likely.
Last year, in a book titled The End of Sex, he predicted half of
couples would stop reproducing naturally by 2040, instead
relying on synthetic reproduction using skin or blood as a
Others say it’s possible, even probable, that lab-made
gametes could be genetically engineered to remove disease
risks. And still more speculative possibilities are on the horizon. For instance, scientists believe it will be possible to
make eggs from a man’s skin cell and sperm from a woman’s
skin cell, though the latter would be more di;cult because
women lack Y chromosomes. This process, termed “sex reversal,” in theory could allow reproduction between two people
of the same sex. And then there is what Greely terms the
“uni-parent—his own sperm, his own egg, his own ‘unibaby.’”
Such bizarre possibilities have dominated news coverage of
recent advances. The episode of All Things Considered that
B.D. heard on the radio asked whether it would be possible to
steal a hair from George Clooney’s head and create a clandestine Hollywood sperm bank.
Reijo Pera, now vice president for research at Montana
State University, thinks such speculation is misleading and
harmful. “I don’t view something like in vitro gametogenesis as something scary. I see a group of people that is hurting,” she says. She also doubts people will go out of their way
to obtain a lab-made baby if they don’t need to. “I think that
it would grieve people who are infertile to hear those questions,” she says. “Because people who can reproduce the natural way—well, that’s what they do. I might be naïve, but I
think the way to have a healthy child is still two people get
together and you have wine and dinner.”
As a postdoctoral fellow in the 1990s, Reijo Pera helped to
identify genes that cause total loss of sperm in men. One no-sperm gene, called DAZ, was particularly interesting because
it exists only in primates. It means that in addition to our
thumbs and our intellect, there are details of human reproduction that are also unique.
The problem for scientists is that many of these details
are hidden from view. Scientists are allowed to keep embryos