On Human Cloning
Dr. Lee Silver, a molecular biologist at Princeton University, is author of Remaking Eden: How Genetic Engineering and Cloning Will Transform the American Family (Avon, 1998). In this interview, Silver argues why we should not only not fear human cloning but should embrace it for the many benefits it will bring.
NOVA: Why is the idea of human cloning so frightening?
Silver: In 1997 when Dolly was announced to the world, the word clone
already existed in almost every language in the world, and to people it meant
xeroxing, making a copy of something or somebody. There was a very popular
movie called Multiplicity, in which a man had too much to do in his
life, so he stamped out extra copies of himself. So when people heard the word
cloning, they thought that it was now possible to replicate a human
being, including maybe the human soul. People were frightened to death that
scientists somehow had gained control over human life.
Most people who answered a survey in which 95 percent of them said they were
against human cloning didn't understand what cloning was to scientists. The
word means something very different to scientists than it does to the lay
public. To a scientist, the only thing that a clone is is an organism that has
the same genetic information as another organism. So people eat clones all the
time. We eat bananas. Bananas are produced by cloning, seedless grapes must be
produced by cloning, and there are millions of human clones walking the face of
the Earth right now. We call them identical twins. They are clones. They have
the same genetic information, and yet we know they are different people, and
they have no problem with their individuality.
NOVA: So what can cloning really do?
"There are millions
of human clones walking the face of the Earth right now. We call them identical
Silver: The only thing that human cloning could ever do reproductively is allow
the birth of a child who would be genetically equivalent only in genes to
somebody else who already existed. It would be like a later-born identical
twin, except the social relationship would be different, because the child
would probably be born to a person who would want to treat it as a child,
rather than as a twin.
So instead of having your genetic material come from two people, you have your
genetic material come from one person. But nobody is going to know that child
is a clone, unless the mother tells someone, because all babies look just like
babies, and even as the child is growing up, you'll never know the child is a
clone. Because it just might look like the mother by chance, and it might
behave like the father by chance. So there's no way you'll ever know a child is
a human clone, rather than just a kid who happens to be like the parent by
NOVA: I was going to ask you what a cloned child would be like.
Silver: Genetic information provides a framework for human life. It provides us
with our potential to grow to a certain height, our predisposition to certain
diseases, and even predispositions to certain behaviors. But the environment
acts upon and modifies the genetic endowment, and there's a third component,
our own consciousness, which allows us to go against both our genes and our
So a child born by cloning, what I would call a mono-parental child, would have
some similarities to the parent, but it would be his or her own person. A lot
of people say it's horrible that egomaniac men are going to want to cheat
mortality by cloning themselves. I say to them, "Well do you know what an
egomaniac man is going to get from this process? First, he's going to have to
find a surrogate mother to gestate the embryo and fetus. Then this child is
going to be born. It's going to be a little boy, who grows up into a big boy,
who doesn't listen to his father."
"There's no other reason to use
cloning technology, except to allow infertile people to have babies. It doesn't
serve any other purpose."
That's because every child is ultimately unpredictable and uncontrollable. So
who wants an unpredictable, uncontrollable child? Well, every adult who has
ever decided to have children does it, knowing they're going to have an
unpredictable, uncontrollable child. There's no other reason to use cloning
technology, except to allow infertile people to have babies. It doesn't serve
any other purpose.
NOVA: What I keep hearing everybody say is the only thing holding everyone back
are the safety issues.
Silver: That's correct.
NOVA: So what are some of those?
Silver: It's perfectly clear that if cloning works in every other mammal in
which it's been tried, it will work in human beings. But at the moment, there
is a pretty high frequency of birth defects in these other animals. There are a
large number of cloned calves that are born too big and have health problems.
As long as that frequency of birth defects is high, and we can't control it,
then it would be unethical to use this technology to try to bring about the
birth of a child.
"It's perfectly clear that if cloning
works in every other mammal in which it's been tried, it will work in human
But there's a way around this problem. If we understand what the cause of the
birth defect is, you should be able to select embryos at the outset that are
not going to have the birth defect and start the process with an embryo that
you know is going to avoid this birth defect. Once that happens, the safety
issues will probably go away.
NOVA: Another doctor said to me, "Look, it took them so many tries. It's such
an inefficient process."
Silver: Well, there was a reproductive technology in which the doctors who
developed this technology went through the first 103 women without a single
success, and, finally, on the 104th time, they got a success. That technology
was in vitro fertilization, and it took Patrick Steptoe and Robert
Edwards [who, in 1978, brought about the birth of Louise Brown, the first
baby conceived outside her mother's womb] 104 times to get one baby, that's a
success rate of less than one percent.
Ian Wilmut [who orchestrated the birth of Dolly] put cloned embryos into 13
surrogate mothers, and one got pregnant and had offspring. So the success rate
of cloning was much greater in the very first experiment than the original
success rate of IVF, and the success rate of cloning has become much, much,
much better as the technology has become optimized, just like the IVF success
rate has become better with optimization of the technology.
NOVA: At first wasn't there a fear that cloned animals like Dolly were going to
be prematurely aged?
"The success rate of cloning has become much, much, much
better as the technology has become optimized."
Silver: During the normal process of aging, our cells' chromosomes' tips become
shorter and shorter. When the tips of our chromosomes become too short, the
cell dies and, in fact, the body containing those cells dies with it. So there
was a worry that if you take a cell from an adult animal, whose chromosome tips
have already begun to become shortened, and you took that cell and brought into
existence a new animal, that cloned animal would start its life at a higher
level in the aging process.
So people feared that Dolly was prematurely aged. And when Dolly's chromosomes
were looked at, the tips of her chromosomes were a little bit shorter than one
would expect for animals her age. So everybody said, "Oh, Dolly is prematurely
Now, if you actually look at the animal, she is not prematurely aging. She is
exactly the way you would expect for animals her age. It turns out that her
chromosome tips were just a little bit shorter than expected and probably
within the range of normality for her age.
NOVA: The newest research is showing that these animals are not aging, but, in
fact, they might even be younger?
Silver: New research has come out that shows that contrary to what people
thought originally, the cloning process rejuvenates cells. We can understand
why that happens, because during the normal process of embryogenesis, when the
embryo is normally developing, the chromosome tips get longer. That's the
reason we can exist as a species generation after generation after generation.
It's during embryogenesis that chromosomes are rejuvenated. And, in fact,
cloning rejuvenates the chromosomes of the cell that the chromosomes came
NOVA: So besides helping infertile couples have babies, how else could cloning
help people? One thing you mention in your book is how cloning could bypass
certain genetic disabilities that could be passed on.
Silver: I think the best example I'll give you is the following: In the normal
course of reproduction by sexual intercourse about four percent of children are
born with birth defects. A major cause of birth defects is that when the sperm
and eggs are being made, their genetic material is being divided in half, and
in that process, sometimes the division doesn't work exactly right, and
sometimes eggs or sperm end up with one too many chromosomes, and that causes
"Cloning bypasses the process of
dividing the DNA in half, so you would expect animals produced by cloning to
have fewer chromosomal problems."
Cloning bypasses the process of dividing the DNA in half, so you would expect
animals produced by cloning to have fewer chromosomal problems, and you'd
reduce that cause of birth defect.
The other birth defect problem is caused when two parents unknowingly are
carriers for a disease like sickle-cell anemia or cystic fibrosis, and then 25
percent of their children are going to have that awful disease. With cloning
you bypass that. Because if the adult doesn't have sickle-cell anemia or some
disease like that, the child won't have that disease either. Now, cloning may
cause other kinds of birth defects, which will need to be controlled before the
technology could be used for human reproduction.
NOVA: You also mention advantages that cloning could have that have nothing to
do with reproduction.
Silver: Let me give you an example. If you have leukemia, you will die unless
you can find a bone-marrow transplant. The problem is, if you take a random
person off the street and use that person's bone marrow to put into your body,
there will be a rejection. Your body will recognize that bone marrow as foreign
and will reject it. Ideally, you'd like to have an identical twin, because you
could take the bone marrow from your identical twin and put it into you, and
your body wouldn't see it as foreign, because genetically it's the same.
What cloning will allow scientists to do in the future is to take a cell from
your body and reprogram it—like rebooting a computer back to the embryonic
state—and guide that cell to develop into a particular tissue or organ. So
you could guide that embryonic cell into bone marrow, and then you can put the
bone marrow back into that person, who actually donated the cell in the first
place, so you're giving that person his or her own bone marrow.
"All kinds of tissues could be regenerated through the cloning process to allow
people to survive pretty awful diseases."
Or for Parkinson's disease patients, you're giving the person his or her own
neurons, not somebody else's neurons. And all kinds of tissues could be
regenerated through the cloning process to allow people to survive pretty awful
diseases, by giving them their own cells back into their bodies. So this is a
very, very powerful use of the technology, which could overcome disease and
suffering. And most scientists think this is a perfectly valid use of the
NOVA: So you're never allowing these cloned cells to develop into a
Silver: I think it's important to understand that we understand the process of
development so well that you could take a one-cell embryo, which is not
differentiated yet, and by putting certain proteins on that embryo, you can
make that embryo grow into bone marrow. Not a fetus, not a child, just a mass
of tissue. And so you can turn an embryo into a mass of tissue that has no kind
of conscious ability or anything like that. Then you can take this tissue and
give it back to the person who produced the cell in the first place. I think
this is a perfectly legitimate use of cloning technology that everybody should
be able to accept.
NOVA: And you would argue that, when and if it happens, using cloning to
produce human babies is not something we should worry about?
Silver: People are upset about human cloning, when I'm quite confident that
human cloning will never have an impact on society, because most people want to
have children with their partners.
At the moment, cloning provides a way for sterile people to have biological
offspring. But we're going to go beyond cloning, where it's possible to take a
skin cell, and turn a skin cell into an egg or turn a skin cell into sperm.
This means that we will be able to overcome the worst cases of sterility and
then allow people to do what they always wanted to do, which is to have
children with their partner.
"I'm quite confident that human
cloning will never have an impact on society, because most people want to have
children with their partners."
There will be very, very few cases in which people really are going to want to
have children by themselves. The only legitimate case I can think of is a 35-
or 40-year-old woman who doesn't have a partner and who wants to have a baby by
herself. She won't need a sperm donor, who can bring in all sorts of terrible
diseases. She'll just say, "Well, why do I need a sperm donor? I'm just going
to use my own genetic material to have a child, since I'm going to raise it
For most other people, for 99 percent of the population, they'll use new
reproductive technologies to have babies that have two parents, and we're back
to where we began.
NOVA: You've stated, in fact, that genetic engineering could have a much
greater impact on society than human cloning.
Silver: Genetic engineering is so much bigger than cloning, and people don't
realize it. Genetic engineering has been with us for 20 years, and when it
first came out in 1980, people didn't understand it enough to be able to be
afraid of it, when, in fact, genetic engineering is much more scary than
Silver: Genetical engineering is already perfected in animals, and it can
produce incredible outcomes. We can produce mice that have been engineered not
to get cancer. We can produce mice that have much, much greater learning and
memory ability. In theory, we can use the same technology on human embryos to
provide all sorts of health advantages to the children that emerge from those
embryos. And we can go beyond that. Once we understand the genes behind
personality behavior and cognitive traits, parents are going to be able to give
their kids all sorts of cognitive advantages in life.
There's no question this technology can be used in this way. Most scientists
are afraid to talk about it in public, because they're afraid of the reaction,
but there's no geneticist today who will tell you this can't be done. They will
tell you it won't be done; people won't want to do this. And I disagree,
because I think that once the technology is usable in a safe way, parents will
jump at the chance to give advantages to their children.
"Genetic engineering is much more scary
NOVA: What's so scary about that?
Silver: The scary part is the ethical dilemma that arises between the rights of
individual parents who want to advantage their child and the good of society as
a whole. Here those two notions come into severe conflict with each other,
because genetic engineering will allow the affluent part of Western society,
which will eventually include the middle class, it will allow this large group
of Americans and people in other Western societies to jump ahead in terms of
the advantages their children start life with. It will increase the gap between
those who have money—countries with money, people with money—and those
who don't. It will cause a permanent division potentially between these two
groups of people, and that would be pretty bad for humanity.
NOVA: What do you mean by permanent? Do you mean they would reach a point where
they would be genetically incompatible?
Silver: Let me tell you the two problems with this. Today, genes are handed out
randomly, which means that even in the worst ghetto in the worst city in the
world, there are children being born who have the potential to succeed as much
as any child coming out of an upper-class neighborhood, because at the level of
birth, there is the same kind of genetic diversity across the entire world. So
that's kind of good. There's a limit to how far people who are in the upper
socioeconomic class can go relative to people in the lower socioeconomic class.
In theory, people can jump from the bottom class to the top class in every
"It could reach the point where people in the upper
genetic class could no longer breed with people who were not genetically
With genetic engineering, it might stop that process, because if the upper
class is able to give its children, grandchildren, and great-grandchildren more
and more and more genetic advantages, they will move the class so far away from
the people who are naturally born that the people in the natural class will
have no way of jumping into this upper class, and that would be a permanent
divide in society.
Eventually, if this went on long enough, it could reach the point where people
in the upper genetic class could no longer breed with people who were not
genetically engineered, which would lead to a division of our species into two
or more separate species.
Back to On Human Cloning
Interview conducted by Sarah Holt, producer, "18 Ways to Make a Baby"
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