Twenty years ago, bioengineers fiddled with plastic and
wires and transducers while building gizmos. Today, a
bioengineer is more likely to be tinkering with cells and
chromosomes and genes while deciphering the stuff of
 Gregory Stock's book "Redesigning Humans: Our Inevitable
Genetic Future" preaches the promise of bioengineering-longer life
and health spans, smarter children, better genes. The
question Stock addresses is not "Should we genetically redesign
humans?" or even "Are there limits to such molecular tinkering?"
but rather "How do we best get to our inevitable future?"
 Stock is well positioned to lead such a discussion.
Holding a doctorate in biophysics from Johns Hopkins University and
a MBA from Harvard University, Stock directs the Program on
Medicine, Technology, and Society at UCLA's School of Public
Health. His passion is the exploration of critical
technologies that are primed to have large impacts on humanity's
future and the character of medical science. "Redesigning
Humans: Our Inevitable Genetic Future" won the Kistler Book Prize
for science books and was nominated for a Wired Rave
 From page 1, Stock shows himself to be an enthusiastic
optimist, pragmatic about the redesigning of humans from the genes
up. He writes, "We know that Homo sapiens is not the final
word in primate evolution, but few have yet grasped that we are on
the cusp of profound biological change, poised to transcend our
current form and character on a journey to destinations of new
imagination." This is no Darwinian non-progressive
evolutionary process, but evolution as directed, conscious human
 Peppered throughout the book, bold claims about the
potential to manipulate our evolutionary trajectory challenge our
deepest values and push us towards a serious public debate on the
future of genetic medicine and bioinformatics. Although Stock
would happily lead us towards a broad-based acceptance of human
evolutionary control, the result may be more modest-an increase in
the reader's understanding of the science poised to bring in the
genetic future and a sense of incredible awe and healthy concern
about that future, inevitable or not.
 Stock realizes that as we understand how genes work to shape
who we are and to influence our health, we will want to make
decisions about our own genetic make-up and, more importantly, that
of our children. "Redesigning Humans" focuses on the
technology for and the implications of choosing certain genetically
influenced characteristics for our offspring in order to protect
them from disease, increase their intelligence, and give them other
desired attributes. Technologically, how might we go about
this? Genetic engineering? Inserting auxiliary
chromosomes? Reproductive cloning?
 Importantly, Stock sees the interest in human reproductive
cloning as the red herring that it is-a needless distraction from
the vital issues of embryo selection, genetic manipulation, and
genetic enhancement. Although the idea of a delayed genetic
twin is hauntingly strange, the birth of a "cloned child"-if and
when it occurs-will have little lasting impact on most of us, on
our values, or on our children.
 Human redesign and evolutionary control will come about
through germline genetic engineering-that is, specifically changing
the genetic complement of the fertilized egg so that the
alterations are passed to subsequent generations. Extensive
modifications of human hereditary material of the kind Stock
envisions will require safe and dependable methods for germline
intervention. Performing genetic surgery one person at a time
is simply unworkable. Germline technology will allow humanity
to rig the genetic lottery-ostensibly guaranteeing genetically
enhanced, disease-resistant future generations.
 In Stock's view, such "germline interventions" will involve
the addition of artificial chromosomes-for example, adding numbers
47 and 48 to the zygote's original 46. Since artificial human
chromosomes provide a stable platform for adding desired genetic
material to cells, they will provide the precision and reliability
that germline engineering requires.
 These artificial human chromosomes will be chemically
identical to those naturally occurring in our cells-twisted ladders
of DNA. Possessing packets of genes and their control
sequences, artificial chromosomes could become a universal genetic
delivery system. Since there is no manipulation of the 3
billion base pairs on a person's 46 naturally occurring
chromosomes, artificial chromosomes minimize the possibility of
derailing existing genetic interactions. In fact, modules of
genes could be delivered via such auxiliary chromosomes and turned
on and off with the flick of a chemical switch.
 According to Stock, the vast potential of human auxiliary
chromosomes to combat disease and to upgrade genes will become so
desired that "laboratory conception" will become obligatory in
order to avoid the potential harms of "natural conception."
If he is right, we will have arrived at the gates of the
genetically engineered world of the movie GATTACA.
 Stock engages the reader in a thought experiment.
Remembering that humans have 46 chromosomes, imagine that a future
father has chromosome 47, version 2.0, containing a dozen
therapeutic gene packets, injected into the fertilized egg that
nine months later is his daughter. However, when the daughter
is grown, she finds this version to be utterly prehistoric and
wants her son to get the upgraded version 5.9, which better
regulates gene expression and provides protection against many more
types of cancer with fewer side effects than version 2.0. The
daughter cannot imagine giving her son an outdated version of
chromosome 47 nor reverting to the old days of 46 naturally
occurring chromosomes. Wouldn't all parents choose version
5.9 as the daughter has done?
 Stock denies that scenarios such as this are impossible or
sheer fantasy. Our impulse is to do whatever we can to
benefit our children. Hence, we will intervene and, "[t]he
biggest challenge we will face from germline technology is not from
its failure . . . . Success is what will tax our wisdom,
because that would force us to come to grips with the medical,
social, political, and philosophical implications of self-directed
human evolution. The injection of artificial chromosomes
loaded with genetic supplements . . . may prove to be humanity's
best hope, and its worst fear."
 Indeed, Stock's longed-for, inevitable genetic future ought
to tax our wisdom, but not in the way he imagines. His
overarching theme is that selecting and altering embryos through
germline modifications-the most promising method for human
redesign-will "write a new page in the history of life, allowing us
to seize control of our evolutionary future." Bold
technological advances in the understanding of human genetics and
reproduction as well as animal transgenics will allow humans to
make fundamental choices about the genetic make-up of their
children and their children's children. Such selective
reproduction is much more efficient at spreading successful genes
that traditional procreation. The future human will,
according to Stock, be "much more than simply human."
 But is our proper goal to be "much more than simply human"
or to be "simply human" in the best way possible? As any
viewer of GATTACA 's predictable world of genetic "valids" and
"in-valids" knows, there's much more to being simply human than
"successful genes." And, even if we could steer human
evolution, toward what end would-or should-we aim?
 Stock does not ignore consequences; indeed his thinking is
all about the future. He thoughtfully raises ethical concerns
arguing that the moral crux is not the potential for abuse of
genetic technology but that we do not know the long-term effects of
its use. However, rather than appealing to the precautionary
principle-that in instances of profound uncertainty and sizable
risk, it is best to err on the side of caution-Stock insists that
slowing down and devising an appropriate course of action is "a
mirage." We simply cannot find the brakes.
 Seemingly, nothing can thwart our drive to manipulate human
heredity. The title's mantra of "inevitability" permeates the
book. For Stock, "[r]emaking ourselves is the ultimate
expression of our humanity." There is really nothing to be
done, as genetic and reproductive technologies will be "impossible
to control." And to those who hesitate, who not only
acknowledge but worry about consequences, both predictable and
unforeseen, he simply says, "If biological manipulation is indeed a
slippery slope, then we are already sliding down that slope now and
may as well enjoy the ride."
 I am no fan of traditional slippery slope arguments as they
often leave us paralyzed by the fear of slipping into the ethical
abyss. I am less a fan of Stock's reverse slippery slope
argument that leaves us no choice about taking the plunge.
Nonetheless, confronting the slippery slope reveals something
important about our humanity-that we are apt to be carried away
with ourselves. Since we cannot be trusted to stop,
traditional arguments would have us avoid the slope
altogether. Since we cannot be trusted to go, Stock would
give us a shove.
 Most of us travel through life traversing slippery
slopes. The first time we fib, we set foot on a slippery
slope that can lead to fraud-yet few of us inevitably go from white
lies to jail time. Our daily ethical practice involves
walking down and stopping on slippery slopes. The ethical
task is to erect carefully considered barriers below which we
refuse to fall.
 Ethics is about setting limits, and Stock's argument from
inevitability neither does us justice nor does justice to us.
"Is" does not equal "ought" and "can" does not imply
"should." Because any and all germline interventions impact
future generations, it is the responsibility of the present
generation to choose wisely. That we will face such choice is
"inevitable"; a particular choice, or a particular future, is
 Despite the sense of "inevitability" or perhaps because of
it, "Redesigning Humans" helps set the stage for personal and
public deliberation on the genetic future. Stock has penned a
real page-turner, a book written with a clarity that can be
appreciated by scientists and genetic novices alike. Although
one can-and should-question his lavish predictions regarding
genetic diversity and evolution, Stock's use of real-life examples
and thought experiments grounds the cutting-edge science.
Whether you agree with his thought-provoking vision of humanity's
future or not, you will develop an appreciation for genetic science
and its potential applications to alleviate human suffering and to
control human evolution.
 Although more modest than Stock's intent, in my view,
"Redesigning Humans" makes two important contributions to our
thinking about the genetic future. The first is his leading
the reader through the "small step" approach to germline
modification by demonstrating that there are merely a series of
small steps from in vitro fertilization to embryo screening-both of
which are done today-to germline engineering. He
writes, "Direct germline intervention is the logical
conclusion of our ongoing progress in reproductive biology and the
ultimate expression of it, and its realm will likely be human
enhancement." In fact, all science works by increments.
What appears to be a giant leap is really a series of small
steps-each of which can raise ethical and theological
 The second notable contribution is that biotechnology in
general and genetics in particular are currently governed by an
ethics of free choice and free markets. Stock accepts market
controls but few other limits. "A major safeguard that
capitalism offers against questionable reproductive technologies is
that unless they appeal to a significant number of people, the
procedures have no profit potential and fade away or are not even
developed. . . . [T]he reproductive and genetic technologies
. . . we see first will likely be those with large potential
markets." What determines right from wrong seems to be the
desire of parents to pay for particular traits and not for
others. Emphasizing the role of financial interests in
science, Stock cedes the ethical ground to the marketplace.
Although I find Stock's position in this regard troubling-how do
markets assure safety and guard against discrimination, for
example-it is crucial to realize the role that financial incentives
and profit play in 21st century medicine.