The Wisdom of Nature: An Evolutionary Heuristic for Human Enhancement

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T h eW i s d o mo fN a t u r e :
An Evolutionary Heuristicfor Human Enhancement
Nick Bostrom and Anders Sandberg∗
Abstract
Human beings are a marvel of evolved complexity. Such systems can
be difﬁcult to enhance. When we manipulate complex evolved systems,which are poorly understood, our interventions often fail or backﬁre.It can appear as if there is a ‘‘wisdom of nature’’ which we ignore atour peril. Sometimes the belief in nature’s wisdom—and correspondingdoubts about the prudence of tampering with nature, especially humannature—manifest as diffusely moral objections against enhancement. Suchobjections may be expressed as intuitions about the superiority of thenatural or the troublesomeness of hubris, or as an evaluative bias infavor of the status quo. This chapter explores the extent to which suchprudence-derived anti-enhancement sentiments are justiﬁed. We developa heuristic, inspired by the ﬁeld of evolutionary medicine, for identifyingpromising human enhancement interve ntions. The heuristic incorporates
the grains of truth contained in ‘‘nature knows best’’ attitudes whileproviding criteria for the special cases where we have reason to believe
that it is feasible for us to improve on nature.
1.I n t r o d u c t i o n
1.1. The wisdom of nature, and the special problem of enhancement
We marvel at the complexity of the human organism, how its various parts
have evolved to solve intricate problems: the eye to collect and pre-process
∗Oxford Future of Humanity Institute, Faculty of Philosophy and James Martin 21st Century
School, Oxford University. Forthcoming in Enhancing Humans , ed. Julian Savulescu and Nick Bostrom
(Oxford: Oxford University Press)
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visual information, the immune system to ﬁght infection and cancer, the
lungs to oxygenate the blood. The human brain—the focus of many of
the most alluring proposed enhancements—is arguably the most complex
thing in the known universe. Given how rudimentary is our understanding
of the human organism, particularly the brain, how could we have any
realistic hope of enhancing such a system?
To enhance even a system like a car or a motorcycle—whose complexity
is trivial in comparison to that of the human organism—requires a fair bit
of understanding of how the thing works. Isn’t the challenge we face in
trying to enhance human beings so difﬁcult as to be hopelessly beyond our
reach, at least until the biological sciences and the general level of human
abilities have advanced vastly beyond their present state?
It is easier to see how therapeutic medicine should be feasible. Intuitively,
the explanation would go as follows: Even a very excellently designed
system will occasionally break. We might then be able to ﬁgure out what
has broken, and how to ﬁx it. This seems much less daunting than to take
a very excellently designed, unbroken system, and enhance it beyond its
normal functioning.
Yet we know that even therapeutic medicine is very difﬁcult. It has been
claimed that until circa 1900 , medicine did more harm than good. ¹And
various recent studies suggest that even much of contemporary medicine
is ineffectual or outright harmful. ²Iatrogenic deaths account for 2to4
percent of all deaths in the US (the third leading cause of death according
to one accounting ³) and may correspond to a loss of life expectancy by 6to
12months. ⁴We are all familiar with nutritional advice, drugs, and therapies
that were promoted by health authorities but later found to be damaging
to health. In many cases, the initial recommendations were informed by
large clinical trials. When even therapeutic medicine, based on fairly good
data from large clinical trials, is so hard to get right, it seems that a prudent
person has much reason to be wary of purported enhancements , especially
as the case for such enhancements is often based on much weaker data.
Evolution is a process powerful enough to have led to the development of
systems—such as human brains—that are far more complex and capablethan anything that human scientists or engineers have managed to design.
¹McKeown and Lowe 1974 .
²Newhouse and Group. 1993 ; Frech and Miller 1996 ; Kirsch, Moore, Scoboria, and Nicholls 2002 .
³Starﬁeld 2000 . ⁴Bunker 2001 .
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Surely it would be foolish, absent strong supporting evidence, to suppose
that we are currently likely to be able to do better than evolution, especially
when so far we have not even managed to understand the systems that
evolution has designed and when our attempts even just to repair what
evolution has built so often misﬁre!
We believe that these informal considerations contain a grain of truth.
Nonetheless, in many particular cases we believe it is practically feasibleto improve human nature. The evolution heuristic is our explanation of
why this is so. If the evolution heuristic works as we suggest, it shows that
there is some validity to the widespread intuition that nature often knows
best, especially in relation to proposals for human enhancement. But the
heuristic also demonstrates that the validity of this intuition is limited, by
revealing important exceptional cases in which we can hope to improve
on nature using even our present or near-future science and technology.
The evolution heuristic might be useful for scientists working to develop
enhancement technologies. It might also be useful in evaluating beliefs
and arguments about the ethics of human enhancement. This is because
intuitions about the wisdom of nature appear to play an important role
in the cognitive ecology of many anti-enhancement advocates. While
sophisticated bioconservatives (aware of the distinction between ‘‘is’’ and‘‘ought’’) may not explicitly base their arguments on the alleged wisdom
in nature, we believe that such intuitions inﬂuence their evaluation of the
plausibility of various empirical assum ptions and mid-level moral principles
that are invoked in the enhancement discourse; just as the opinions and
practical judgments of the pro-enhancement transhumanists look more
plausible if one assumes that nature is generally unwise. Addressing such
hidden empirical background assumptions may therefore help illuminate
important questions in applied ethics. ⁵
1.2. The evolution heuristic
The basic idea is simple. In order to decide whether we want to modify
some aspect of a system, it is helpful to consider why the system has
that aspect in the ﬁrst place. Similarly, if we propose to introduce some
new feature, we might ask why the system does not already possess it.
⁵On the role of mid-level principles in one area of applied ethics, see Beauchamp and Childress
1979 .
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The system of concern here is the human organism. The question why
the human organism has a certain property can be answered on at least
two different levels, ontogeny and phylogeny. Here the focus is on the
phylogeny of the human organism.
We can conceive of a proposed enhancement as an ordered pair ( α,A),
where αis some speciﬁc intervention (e.g., the administration of a drug)
andAis the trait that the intervention is intended to realize (e.g., improved
memory consolidation). We deﬁne an enhancement as an intervention that
causes either an improvement in the functioning of some subsystem (e.g.
long-term memory) beyond its normal healthy state in some individual or
the addition of a new capacity (e.g. magnetic sense).
On this deﬁnition, an enhancement is not necessarily desirable, either
for the enhanced individual or for society. For instance, we might have
no reason to value an enhancement of our sweat glands that increases
their ability to produce perspiration in response to heat stimuli. In other
instances, we might beneﬁt from increased functionality or a new capacity,
and yet not beneﬁt from the enhancement because the intervention also
causes unacceptable side-effects. ⁶The evolution heuristic is a tool to help
us think through whether some proposed enhancement is likely to yield a
net beneﬁt.
The starting point of the heuristic is to pose the evolutionary optimality
challenge :
(EOC) If the proposed intervention would result in an enhancement, why
have we not already evolved to be that way?
Suppose that we liken evolution to a surpassingly great engineer. (The
limitations of this metaphor are part of what makes it useful for our purposes.)
Using this metaphor, the EOC can be expressed as the question, ‘‘How
could we realistically hope to improve on evolution’s work?’’ We propose
that there are three main categories of possible answers, which can be
summarized as follows:
•Changed tradeoffs. Evolution ‘‘designed’’ the system for operation in
one type of environment, but now we wish to deploy it in a very
different type of environment. It is not surprising, then, that we might
⁶Which side-effects are acceptable depends, of c ourse, on the beneﬁts resulting from the enhance-
ment, and these may vary between subjects depending on their goals, life plans, and circumstances.
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be able to modify the system better to meet the demands imposed
on it by the new environment. Making such modiﬁcations need not
require engineering skills on a par with those of evolution: consider
that it is much harder to design and build a car from scratch than it
is to ﬁt an existing car with a new set of wheels or make some other
tweaks to improve functioning in some particular setting, such as icy
roads. Similarly, the human organism, whilst initially ‘‘designed’’ foroperation as a hunter-gatherer on the African savannah, must now
function in the modern world. We may well be capable of making
some enhancing tweaks and adjustments to the new environment
even though our engineering talent does not remotely approach that
of evolution.
•Value discordance. There is a discrepancy between the standards by
which evolution measured the quality of her work, and the standards
that we wish to apply. Even if evolution had managed to build the
ﬁnest reproduction-and-survival machine imaginable, we may still
have reason to change it because what we value is not primarily to
be maximally effective inclusive-ﬁtness optimizers. This discordance
in objectives is an important source of answers to the EOC. It is
not surprising that we can modify a system better to meet our goals,if these goals differ substantially from the ones that (metaphorically
might be seen as having) guided evolution in designing the system
the way she did. Again, this explanation does not presuppose that
our engineering talent exceeds evolution’s. Compare the case to that
of a mediocre technician, who would never be able to design a car,
let alone a good one; but who may well be capable of converting
the latest BMW model into a crude rain-collecting device, thereby
enhancing the system’s functionality as a water collecting device.
•Evolutionary restrictions. We have access to various tools, materials, and
techniques that were unavailable to evolution. Even if our engineering
talent is far inferior to evolution’s, we may nevertheless be able to
achieve certain things that stumped evolution, thanks to these novel
aids. We should be cautious in invoking this explanation, for evolutionoften managed to achieve with primitive means what we are unable to
do with state-of-the-art technology. But in some cases one can show
that it is practically impossible to create a certain feature without some
particular tool—no matter how ingenious the engineer—while the
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same feature can be achieved by any dimwit given access to the right
tool. In these special cases we might be able to overcome evolutionary
restrictions.
In the following three sections, we will explore each of these categories
of possible answers to the EOC in more detail, and show how they can
help us decide whether or not to go ahead with various potential human
enhancements.
Our ideas about enhancement in many ways parallel earlier work in
evolutionary medicine. Evolutionary medicine is based on using evolu-
tionary considerations to unde rstand aspects of human health. ⁷ Host s and
parasit es have adapted to one another, and analysis of the tradeoffs involved
can reveal adaptations that contributed to ﬁtness in the past but are mal-
adaptive today, or symptoms that have been misdiagnosed as harmful but
may actually aid recovery. Evolutionary medicine also helps explain the
incidence of genetic diseases, which can be maintained in the population
because of beneﬁcial effects in historically normal environments. Another
contribution of evolutionary medicine has been to draw attention to the
fact that our modern environment may not always ﬁt a biology designed
for Pleistocene conditions, and how this mismatch can cause disease. These
insights are recycled in our analysis of human enhancement.
Another strand of research relevant to our aims is evolutionary optim-
ization theory, which seeks to determine the abilities and limitations of
evolution in terms of producing efﬁcient biological functions. ⁸ While,
naively, evolution might be thought to maximize individual ﬁtness (the
expect ed lifetime number of surviving offspring), there are many contexts
in which this simpliﬁcation leads to error. Sometimes it is necessary to
focus on the concept of inclusive ﬁtness, which takes into account the
effects of a genotype on the ﬁtness of blood-relat ives other than direct
descendants. Sometimes a gene-cent ric perspective is needed, to account for
phenomena such as segregation distortion and junk DNA.⁹ There are also
many other ways in which evolution routinely falls short of ‘‘optimality’’,
some of which will be covered in later sections.
⁷Williams and Nesse 1991; Trevathan, Smith and McKenna 1999.
⁸Parker and Smith 1990. ⁹Dawkins 1976; Williams 1996/ 1966.
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2. Changed tradeoffs
2.1. General remarks on tradeoffs
Evolutionary adaptation often involves striking a tradeoff between com-
peting design criteria. Evolution has ﬁne-tuned us for life in the ancestral
environment, which, for the most part, was a life as a member of ahunter-gatherer tribe roaming the African savannah. Life in contemporary
society differs in many ways from life in the environment of evolutionary
adaptedness. Modern conditions are too recent for our species to have fully
adapted to them, which means that the tradeoffs evolution struck may no
longer be optimal today.
In evolutionary biology, the ‘‘environment of evolutionary adaptedness’’
(EEA) refers not to a particular time or place, but to the environment
in which a species evolved and to which it is adapted. ¹⁰It includes
both inanimate and animate aspects of the environment, such as climate,vegetation, prey, predators, pathogens, and the social environment of
conspeciﬁcs. We can also think of the EEA as the set of all evolutionary
pressures faced by the ancestors of the species over recent evolutionary
time—in the case of humans, at least 200,000years. ¹¹Hunting, gathering
of fruits and nuts, courtship, parasites, and hand-to-hand combat with wild
animals and enemy tribes were elements of the EEA; speeding cars, high
levels of trans fats, concrete ghettos, and tax return forms were not.
The import of this for the evolution heuristic is that even if the human
organism were a wonderfully well-designed system for life in the EEA,
it may not in all respects be well designed for life in contemporary
society. If we can identify speciﬁc changes to our environment that have
shifted the optimal tradeoff point between competing design desiderata in
a certain direction, we may be able to ﬁnd relatively easy interventions
that could ‘‘retune’’ the tradeoff to a point that is closer to its present
optimum. Such retuning interventions might be among the low-hanging
fruits on the enhancement tree, fruits within reach even in the absence of
super-advanced medical technology.
¹⁰Hagen 2002. ¹¹Hagen 2002.
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Proposed enhancements aiming to retune altered tradeoffs can often
meet the EOC. The new trait that the enhancement gives us might have
been maladaptive in the EEA even though it would be adaptive now.
Alternatively, the new trait might be intrinsically associated with another
trait that was maladaptive in the EEA but has become less disadvantageous
(or even beneﬁcial) in the modern environment, so that the terms of the
tradeoff have shifted. In either case, the enhancement could be adaptive inthe current environment without having been so in the EEA, which would
explain why we do not have that trait, allowing us to meet the EOC.
We can roughly distinguish two ways in which tradeoffs can change:
new resources may have become available that were absent, or available only
at great cost, in the EEA; or, the demands placed on one of the subsystems
of the human organism may have changed since we left the EEA. Let us
consider these two possibilities in turn and look at some examples.
2.2. Resources
One of the main differences between human life today (for most people
in developed countries) and life in the EEA is the abundant availability
of food independently of place and season. In the state of nature, food is
relatively scarce much of the time, making energy conservation paramount
and forcing difﬁcult energy expenditure tradeoffs between metabolically
costly tissues, processes, and behaviors. As we shall see, increased access
to nutrients suggests several promising enhancement opportunities. Wehave also gained access to important new non-dietary resources, including
improved protection against physical threats, obstetric assistance, better
temperature control, and increased availability of information. Let us
examine how these new resources are relevant to potential enhancements
of the brain and the immune system.
2.2.1.T h e b r a i n The human brain constitutes only 2per cent of body mass
yet accounts for about 20per cent of total energy expenditure. Combined,
the brain, heart, gastrointestinal tract, kidneys, and liver consume 70per cent
of basal metabolism. This forces tradeoffs between the size and capacity of
these organs, and between allocation of time and energy to activities other
than searching for food in greater quantity or quality. ¹²
¹²Aiello, Bates and Joffe 2001 ; Fish and Lockwood 2003 .
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Unsurprisingly, we ﬁnd that, in evolutionary lineages where nutritional
demands are high and cognitive demands low (such as bats hunting in
uncluttered environments), relative brain size is correspondingly smaller. ¹³
In humans, brain size correlates positively with cognitive capacity (. ≈
0.33).¹⁴
Holding brain mass constant, a greater level of mental activity might also
enable us to apply our brains more effectively to process information andsolve problems. The brain, however, requires extra energy when we exert
mental effort, reducing the normally tightly regulated blood glucose level
by about 5per cent ( 0.2mmol/l) for short ( <15min) efforts and more
for longer exertions. ¹⁵Conversely, increasing blood glucose levels has been
shown to improve cognitive performance in demanding tasks. ¹⁶
The metabolic problem is exacerbated during prenatal and early child-
hood growth where brain development requires extra energy. Brain
metabolism accounts for a staggering 60per cent of total metabolism
in newborns, ¹⁷exacerbating the competitive situation between mother and
child for nutritional resources—an unpleasant tradeoff. ¹⁸Children with
greater birth weight have a cognitive advantage. ¹⁹
Another constraint on prenatal cerebral development is the size of the
human birth canal (itself constrained by bipedalism), which historicallyplaced severe constraints on the head size of newborns. ²⁰These constraints
are partly obviated by modern obstetrics and the availability of caesarian
section. One way of reducing head size at birth and perinatal energy
demands would be to extend the period of postnatal maturation. However,
delayed maturation was vastly riskier in the EEA than it is now.
What all this suggests is that cognitive enhancements might be possible
if we can ﬁnd interventions that recalibrate these legacy tradeoffs in ways
that are more optimal in the contemporary world. For example, suppose
we could discover interventions that moderately increased brain growth
during gestation, or slightly prolonged the period of brain growth during
infancy, or that triggered an increase in available mental energy. Applying
the EOC to these hypothetical interventions, we get a green light. We can
¹³Niven 2005 . ¹⁴McDaniel 2005 .
¹⁵Scholey, Harper and Kennedy 2001 ; Fairclough and Houston 2004 .
¹⁶Korol and Gold 1998 ; Manning, Stone, Korol and Gold 1998 ; Martin and Benton 1999 ; Meikle,
Riby and Stollery 2005 . Increasing oxygen levels (another req uirement for metabolism) also improves
cognition (Winder and Borrill 1998 ).
¹⁷Holliday 1986 . ¹⁸Martin 1996 . ¹⁹Matte 2001 . ²⁰Trevathan 1987 .
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see why these enhancements would have been maladaptive in the EEA,
and why they may nevertheless have become entirely beneﬁcial now that
the underlying tradeoffs have changed as a result of the availability of new
resources. If the ‘‘downside’’ of getting more mental energy is that we
would burn more calories, many of us would pounce at the opportunity.
Not all cognitive enhancement interventions get an immediate green
light from the above argument. Stimulants like caffeine and Modaﬁnilenable increased wakefulness and control over sleep patterns. ²¹But sleep
serves various (poorly understood) functions other than to conserve
energy. ²²If the explanation for why we do not sleep less than we do
has to do with these other functions, then reducing sleep might well have
more problematic side-effects than increasing the amount of calories we
need to consume. For any particular intervention, such as the administra-
tion of some drug, we also of course need to consider the possibility of
contingent side-effects, i.e. that the drug might have effects on the body
other than simply retuning the target tradeoff.
2.2.2. The immune system While the immune system serves an essential
function by protecting us from infection and cancer, it also consumes
signiﬁcant amounts of energy. ²³Experiments have found direct energetic
costs of immune activation. ²⁴In birds immune activation corresponded to a
29per cent rise of resting metabolic rate ²⁵and in humans the rate increases
by13per cent per degree centigrade of fever. ²⁶In addition, the protein
synthesis demands of the immune system are sizeable yet prioritized, as
evidenced by a 70per cent increase in protein turnover in children during
infection despite a condition of malnourishment. ²⁷One would expect the
immune system to have evolved a level of activity that strikes a tradeoff
between these and other requirements—a level optimized for life in the
EEA but perhaps no longer ideal.
Such a tradeoff has been proposed as part of an explanation of the placebo
effect. ²⁸The placebo effect is puzzling because it apparently involves getting
something (accelerated recovery from disease or injury) for nothing (merely
²¹Caldwell 2001 . ²²Siegel 2005 . ²³McDade 2003 .
²⁴Demas, Chefer, Talan and Nelson 1997 ; Moret and Schmid-Hempel 2000 ; Ots, Kerimov,
Ivankina, Ilyina and Horak 2001 .
²⁵Martin, Scheuerlein and Wikelski 2003 . ²⁶Elia 1992 .
²⁷Waterlow 1984 ;M c D a d e 2003 . ²⁸Humphrey 2000 .
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having a belief). If the subjective experience of being treated causes a health-
promoting response, why are we not always responding that way? Studies
have shown that it is possible chemically to modulate the placebo response
down ²⁹or up. ³⁰
One possible explanation is that mobilizing the placebo effect consumes
resources, perhaps through activation of the immune system or other
forms of physiological health investment. Also, to the extent that theplacebo response reduces defensive reactions (such as pain, stiffness, and
inﬂammation), it might increase our vulnerability to future injury and
microbial assaults. If so, one might expect that natural selection would
have made us such that the placebo response would be triggered by signals
indicating that in the near future we will (a) recover from our current
injury or disease (in which case there is no need to conserve resources to
ﬁght a drawn-out infection and less need to maintain defensive reactions),
(b) have good access to nutrients (in which case, again, there is no need to
conserve resources), and (c) be protected from external threats (in which
case there is less need to keep resources in reserve for immediate action
readiness). Consistent with this model, the evidence does indeed show that
the healing system is activated not only by the expectation that we will
get well soon but also by the impression that external circumstances aregenerally favorable. For example, social status, ³¹success, having somebody
looking after us, ³²sunshine, and regular meals might all indicate that we are
in circumstances where it is optimal for the body to invest in healing and
long-term health, and they do seem to prompt the body to do just that. By
contrast, conﬂict, ³³stress, anxiety, uncertainty, ³⁴rejection, isolation, and
despair appear to shift resources towards immediate readiness to face crises
and away from building long-term health.
If this model of the placebo response is correct, several potential avenues
of enhancement are worth exploring. One is that since physical safety
and reliable access to food are much improved compared to the EEA, it
might now be beneﬁcial to invest more in biological processes that build
long-term health than was usually optimal in the EEA. We might thus
inquire whether the placebo effect and other evolved responses are ﬂexible
²⁹Sauro and Greenberg 2005 . ³⁰Colloca and Benedetti 2005 .
³¹Sapolsky 2005 . ³²House, Landis and Umberson 1988 .
³³Kiecolt, Glaser, Cacioppo, MacCallum, Snydersmith, Kim and Malarkey 1997 .
³⁴McDade 2002 .
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enough to have adjusted the level of health investment to a level that
is optimal under modern conditions. If not, we could beneﬁt from an
intervention that triggers a placebo-like response or otherwise increases the
body’s health investment.
However, while external stresses and resource constraints are reduced in
the modern environment, the danger of auto-immune reactions remains.
We would therefore have to be careful not to overshoot the target. It ispossible that we would beneﬁt from a lower baseline immune activity in
some parts of the immune system since we are now less at risk of dying
from infectious diseases. As an example, the hygiene theory of allergic
diseases claims that the reduction in immunological challenge in particular
from helminth parasites during early life increases the risk of allergic disease
later in life. ³⁵If true, then a down-regulation of a particular dendritic cell
subpopulation (DC 2) sensitive to helminths, but causing allergic reactions,
might be desirable. Alternatively, an up-regulation of regulatory (DCreg)
cells that tend to be lost in unstimulated immune systems might be used to
control the DC 2cells.
The evolution heuristic also leads us to consider other potential immune
system enhancements. Even if the average activation level of our immune
systems were still optimal in the modern era, we now possess moreinformation (a new resource) about the detailed requirements in speciﬁc
situations. We can use this information to override our bodies’ natural
response tendencies. For example, recipients of donated organs can beneﬁt
from immunosuppressant drugs. Conv ersely, a patient with early-stage
cancer might be better off if her immune system could be induced to
mount an immediate all-out assault on the incipient tumor instead of
conserving resources for hypothetical future challenges. ³⁶
A more radical enhancement would be to improve DNA repair, which
would reduce cancer-causing mutations and improve radiation resistance, at
the price of increasing metabolic needs. The modiﬁcation could be achieved
through overexpression of existing DNA repair genes ³⁷or perhaps even by
transgenic incorporation of the unique abilities of Deinococcus radiodurans. ³⁸
³⁵Yazdanbakhsh, Kremsner and van Ree 2002 ;M a i z e l s 2005 .
³⁶Boon and van Baren 2003 ; Dunn, Old and Schreiber 2004 .
³⁷Wood, Mitchell, Sgouros and Lindahl 2001 .
³⁸Battista, Earl and Park 1999 ; Venkateswaran, McFarlan, Ghosal , Minton, Vasilenko, Makarova,
Wackett and Daly 2000 .
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Increased repair would have to be balanced with apoptosis and replacement
of irreparably damaged cells (another energy cost). Until recently, increased
DNA repair activity might have been too metabolically costly and mutation-
prone for evolution to consider it a worthwhile bargain. One of the most
well-studied pathways, the PARP- 1pathway, protects the genome from
damage but requires so much energy that it can damage cells through
energy depletion. ³⁹
Since the objective of the interventions suggested above is to restore
health, one could argue that they should be regarded as therapeutic rather
than enhancing. But these classiﬁcations are not necessarily incompatible.
We could regard the interventions as therapeutic for the subsystems whose
functioning has been deteriorated by disease, yet enhancing for the immune
system, whose functioning is improved beyond its normal state. ⁴⁰
2.3.D e m a n d s
Just as we have many resources that were denied our hunter-gatherer
ancestors, we also face a different set of demands than they did. This
suggests further opportunities for enhancement.
Changes in demands on the human organism occur when old demands
disappear or are reduced (e.g. less need for long treks to get food;
hygienic surroundings reducing demands on the immune system), and
when demands grow in strength or new demands arise (e.g. greater need to
be able to concentrate on abstract material for long periods; new pathogens
spreading in larger societies). The source and nature of a particular demand
may also change. For instance, exercise is no longer necessary to gain
sustenance, but is instead needed to maintain the body in good shape.
Many ‘‘diseases of civilization’’ are due to these changed demands. For
example, our ancestors needed to exert themselves physically to secure
adequate nutrition, whereas our easy access to abundant food can lead
to obesity. People working indoors do not get the sun exposure that
our ancestors had, leading to vitamin D deﬁciency; ⁴¹yet we risk skin
cancer when we expose pale skin to the sun during occasional recreational
³⁹de Murcia and Shall 2000 ; Skaper 2003 .
⁴⁰In like manner, we can view vaccinations as both th erapeutic (or more accurately, prophylactic)
and as enhancing.
⁴¹Thomas, Lloyd-Jones, Thadhani, Shaw, Deraska, Kitch, Vamvakas, Dick, Prince and Finkelstein
1998 .
388     
activities. Rapid blood coagulation was beneﬁcial in the past, when there
was a high risk of wounding. The increased risk for cardiovascular problems
and embolisms was an acceptable tradeoff. Today, the risk of wounding
has sharply decreased, making the downsides relatively more important.
Reducing coagulation, e.g. by taking low-dose aspirin, can be beneﬁcial
given these changed demands, ⁴²although we risk incidental side-effects
such as stomach irritation.
While the change in demands can cause or exacerbate problems, it can
also alleviate them. The recent emergence of the IT industry appears to
have produced a refuge for people with Asperger’s syndrome where their
preference for structure and detail becomes a virtue and their problems with
face-to-face communication less of a disadvantage. ⁴³Deliberate ﬁtting of
environments to human evolutionary adaptations and individual idiosyn-
crasies is a promising adjunct to direc t human enhancement for improving
human performance and wellbeing.
2.3.1. Literacy and numeracy Intellectual capacity, or at least some speciﬁc
forms of it, seem to have become more rewarded in contemporary society
than they were in the EEA. There is a positive correlation in Western
society between IQ and income. ⁴⁴Higher levels of general cognitive ability
are important not just for highly demanding, high status jobs, but also for
success in everyday life, such as being able to ﬁll out forms, understand news,
and maintain health. As society becomes more complex, these demandsincrease, placing people of low cognitive ability at a greater disadvantage. ⁴⁵
While general cognitive ability may have been advantageous (and selected
for) in our evolutionary past, ⁴⁶
,⁴⁷numeracy and literacy represent more
speciﬁc abilities whose utility has increased dramatically in recent times.
Before the invention of writing, the human brain faced no pressure to
be literate. In the current age, however, literacy is in very high demand.
Failing to meet this demand places an individual at a severe disadvantage
⁴²Force 2002 . ⁴³Silberman 2001 .
⁴⁴Neisser, Boodoo, Bouchard, Boykin, Brody, Ceci, Halpern, Loehlin, Perloff, Sternberg and
Urbina 1996 ; Gottfredson 1997 ; Bersaglieri, Sabeti, Patterson, Vand erploeg, Schaffner, Drake, Rhodes,
Reich and Hirschhorn 2004 .
⁴⁵Gottfredson 1997 ; Gottfredson 2004 . ⁴⁶Gottfredson 2007 .
⁴⁷It should be noted that IQ correlates negatively with fertility in many modern societies (Udry
1978 ; Vancourt and Bean 1985 ; Vining, Bygren, Hattori, Nystrom and Tamura 1988 ). This might be
an example of value discordance betw een human values and evolutionary ﬁtness.
    389
in modern society. Since writing is a relatively recent invention ( 3,500
), and since it is even more recently that written language has become
such a dominant mode of communication, it is plausible that the human
brain is not optimized for modern conditions. The fact that the neural
machinery needed for writing and reading largely overlaps with that needed
to produce and interpret oral communication means that the mismatch
between evolved capacity and present demands is not as great as it mighthave been. Nevertheless, as the phe nomenon of dyslexia demonstrates, it
is possible to have deﬁcits in language processing that are relatively speciﬁc
to written language, possibly arising from minor variations in phonological
processing. ⁴⁸Dyslexia also appears to be linked to enhanced or atypical
visuospatial abilities. ⁴⁹These abilities might have been useful in the EEA,
but today literacy is usually more important for achieving life goals. If our
species had been using written language for a couple of million years and
reproductive ﬁtness had depended on literacy, dyslexia might have been
much rarer than it is.
Modern society also places much greater demands on advanced numerical
skills than we faced in the EEA. In hunter-gatherer societies, numeracy
demands appear to have been limited to being able to count to ﬁve or
ten.⁵⁰In the modern world, one is at a major disadvantage if one cannot
understand at least basic arithmetic. Many occupations require a grasp of
statistics, calculus, geometry, or higher mathematics. Programming skills
open up additional employment possibilities. Good logical and analytical
skills create further opportunities in our information-dense, technology-
mediated, and generally formalized modern society. These skills were much
less useful in the Pleistocene.
The altered nature of the demands we face suggests opportunities for
enhancement by readjusting tradeoffs that are no longer optimal. For
example, number relations appear to be handled by brain circuits closely
linked to spatial cognition of external objects, and affected by spatial
attention abilities. ⁵¹Hence enhancement of this type of spatial attention, ⁵²
possibly at the expense of remote or peripheral attention, could be a
useful enhancement. Similarly, enhancements in reading ability at the
⁴⁸Goulandris, Snowling and Walker 2000 .
⁴⁹von Karolyi, Winner, Gray and Sherman 2003 ; Brunswick, Martin, Marzano and Savill 2007 .
⁵⁰Pica, Lemer, Izard and Dehaene 2004 .
⁵¹McCord 2000 ; Hubbard, Piazza, Pinel and Dehaene 2005 . ⁵²Green and Bavelier 2006 .
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expense of the dyslexia-related visuospatial abilities might gain support
from the EOC.
2.3.2. Concentration The importance of being able to concentrate on
abstract thinking and tasks with little sensory feedback has increased
signiﬁcantly in modern times relative to the importance of peripheral
awareness. In the EEA, peripheral awareness was crucial for detect ing
predators and enemies, while an ability to exclude other stimuli had few
applicat ions. We may hence have evolved attention systems with a tendency
to be too easily distract ed in a modern setting. It has been suggeste d that
ADHD is a form of ‘‘response-readiness’’ that was more adaptive in past
environment s.⁵³ Concentration enhancers may therefore be feasible and
promising in modern settings, enabling users to meet high demands for
sustained attention. Drugs such as methylphenidate (Ritalin) are already
used to treat ADHD and occasionally also for enhancement purposes.⁵⁴
2.3.3. Dietary preferences and fat storage One tradeoff involving food avail-
ability relates to the question of how much nutrition the body should
store in fatty deposits. If high-calorie foods are scarce and food availability
highly variable , it is optimal for an individual to crave high-calorie foods
and to store lots of energy in fat deposit s as insurance against lean times.
We still need an appetite today, and we still need fat deposits, but—at least
in the developed world—they are much less important now than in the
past. Many people’s natural set-points of appet ite and body fat are higher
than optimal, leading to increased morbidity. In wealthy modern societies,
where a Mars bar is never far away, the risks of obesity and diabetes
outweigh the risk of under-nutrition, ⁵⁵ and a sweet tooth is maladapt ive.
This suggests that it might be possible to enhance human health by
ﬁnding effective ways to down-regulate our cravings for fat and sugar, or
by reducing the absorption and storage of these calories in fatty tissues.
Such an enhanceme nt might take various forms: nutritional advice, diet
pills, artiﬁcial sweeteners, indigestible substances that taste like fat, weight-
loss clubs, hypnotherapy, and, in the future, gene therapy. The evolution
heuristic suggests that our natural proclivities to consume and store nutrients
⁵³Jensen, Mrazek, Knapp, Steinberg, Pfeffer, Schowalter and Shapiro 1997.
⁵⁴Farah, Illes, Cook-Deegan, Gardner, Kandel, King, Parens, Sahakian and Wolpe 2004.
⁵⁵Fontaine, Redden, Wang, Westfall and Allison 2003.
    391
might be a case where we could beneﬁt from going against the wisdom
of nature. Independent considerations and possibly further research would
be needed to determine the most effective way of doing this, given that
weight loss itself is a longevity risk factor ⁵⁶and that those who are mildly
overweight have lower mortality than those who are underweight or
obese. ⁵⁷Possibly an aversion to unhealthy foods and eating habits would be
more effective and safer than a general down-regulation of appetite. Theheuristic tells us only that there are no general ‘‘wisdom of nature’’ reasons
to retain our current bodyweight set-points; it does not by itself tell us
which approaches to changing them would be safest.
2.4. The interplay between resources and demands
The picture is complicated by the fact that some phenomena zigzag
across the two subcategories of changed tradeoffs (resources and demands).
Transport vehicles and machinery are new resources that reduce the
demand for physical exertion. The effect is that most of us get less exercise
in the course of our daily routines. Yet our bodies appear to be designed
for physical activity, so a sedentary life causes a variety of health problems.
New resources (gyms, exercise equipment, parks, jogging clubs) have beendeveloped to help us overcome the problems of a sedentary lifestyle. But
now a new demand arises: we need the energy and self-motivation to make
use of these resources—a demand that many ﬁnd it difﬁcult to meet.
In a case like this, there are multiple potential intervention points where
a change could result in an improvement of our lives. One approach
would be to design our environment in such a way as to force us to
be more physically active. Elevators could be removed, motor vehicles
banned from certain areas, and so forth. Another approach would be to
attempt to redesign our bodies so that they would not be dependent on
frequent physical exertion to remain healthy. On this approach, we might
try to develop pharmaceuticals that trigger effects in the body similar to
those normally caused by exercise (such as the IGF- 1/MGF signaling path-
ways, which are stimulated by exercise or muscle damage). ⁵⁸Yet another
approach would be to attempt interventions that increase our energy and
self-motivation, thereby making it easier for us to exercise on our own
⁵⁶Gaesser 1999 . ⁵⁷Flegal, Graubard, Williamson and Gail 2005 .
⁵⁸Baldwin and Haddad 2002 ; Goldspink 2005 .
392     
initiative. For instance, there might be pharmaceuticals that would give us
more energy or strengthen our willpower, or perhaps a habit of regular
workouts instilled in childhood would carry over into adult life.
Whether any of these interventions will work, and, if so, which one
would be the most effective and have the best balance of beneﬁts over
burdens, cannot be determined a priori. This is an empirical question,
whose answer may depend on changing social circumstances, levels oftechnology, personal preferences, and other factors. One should note that it
is not only biological interventions which can have undesirable side-effects.
Removing elevators might cause some health beneﬁts for people forced
to climb the stairs, but it may also deny access for people with mobility
impairments and cause unnecessary inconvenience to others. Encouraging
high levels of physical activity in children might have overall health beneﬁts
but it might also lead to more injuries, more worn-out knees and hip joints
later in life, and less time for non-physical activities.
Another illustration of the complex interplay between new resources
and new demands is offered by the case of addictive drugs. Alcohol, heroin,
and crack cocaine are comparatively novel resources. The availability of
these resources create a new demand on the human organism: the ability
to avoid becoming addicted to harmful drugs that hijack the brain’s rewardsystem. Individuals vary in how they metabolize these drugs and how
their brains react to exposure. Again, the solution might be to develop
new resources (e.g. detox clinics), temporary pharmacological interventions
(methadone), permanent biological modiﬁcations (vaccines), educational
initiatives (drug awareness program s), or social policies (criminalization).
Alternatively, one might attempt to develop safer, non-addictive substitutes
for harmful drugs. ⁵⁹There are many possible ways to defy or to work
around the wisdom of nature.
3. Value discordance
3.1. General remarks on value discordance
We have discussed opportunities for enhancement arising from the changed
tradeoffs we face in the modern world compared to those of the EEA. (A
⁵⁹Nutt 2006 .
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great engineer built a system for use in a certain environment; we adapt it for
use in a different environment.) In this section, we discuss another source of
enhancement opportunities: the discordance between evolutionary ﬁtness
and human values. (A great engineer built a system that efﬁciently serves
one purpose; we tinker with it to make it serve a different purpose.)
While our goals are not identical to those of evolution, there is con-
siderable overlap. We value health, and health increases inclusive ﬁtness.We value good eyesight, and good eyesight is useful for survival. We value
musicality and artistic creativity, and these talents helped to attract mates
in the EEA. If we are hoping to enhance some attribute for which the
concordance in objectives is perfect, the present category will not give any
help in meeting the EOC. We then either have to ﬁnd an answer from
one of the other categories or else suspect that what appears to be an easy
enhancement will in fact come at a large hidden cost.
Whilst some of our traits are both valuable to us and conducive to
ﬁtness, many attributes that we value would either not have promoted
inclusive ﬁtness in our natural environment, or else would not have been
ﬁtness-promoting to a sufﬁcient extent to result in a proﬁle of traits that
is optimal from the perspective of our own values. There is a plethora of
capacities or characteristics to which we assign a value that exceeds thecontribution these characteristics made to survival and reproduction.
One obvious example is contraceptive technology. Vasectomy, birth
control pills, and other contraceptive methods enhance our control over
our reproductive systems, severing the link between sex and reproduction.
We may value such enhancements because they make family planning
easier and increase choice. But evolution would frown on these practices.
The great engineer would not regard the absence of an easy reproductive
off-switch as a defect. When our goals differ from hers, it is unsurprising
that we are able to modify her design in ways that make it better (by our
lights) even if our design skills fall far short of hers. ⁶⁰
We can distinguish (at least) two distinct sources of such value discord-
ance. The ﬁrst is that the characteristics that would maximize an individual’s
inclusive ﬁtness are nor always identical to the characteristics that wouldbe best for her. The other is that the characteristics that would maximize
⁶⁰Evolution might still have the last laugh if in the long run she redesigns our species to directly
desire to have as many children as possible, or to ha ve an aversion against contraceptives. Cultural
‘‘evolution’’ might beat biological evolution to the punch.
394     
an individual’s inclusive ﬁtness are not always identical to those that would
be best for society, or impersonally best. If our goal is to identify potential
interventions that individuals would have prudential reasons for wanting,
then we may perhaps set aside the second source of value discordance. If,
however, we are interested in addressing ethical and public policy matters,
then it is relevant to consider value discordance arising from either of these
two sources. Let us consider each in turn.
3.2. Good for the individual
What characteristics promote individual well-being? There is a vast ethical
and empirical literature on this question, which we shall not attemptto review here. For our purposes, it will sufﬁce to list (Table 1) some
candidate characteristics, ones which may with some plausibility be taken
to be among those that contribute to individual well-being in a wide
range of circumstances. This list is for illustration only. Other lists could be
substituted without affecting the structure of our argument. ⁶¹
Table 1. Some traits that may promote individual well-being
•Emotional well-being
•Freedom from severe or chronic pain
•Friendship and love
•Long-term memory
•Mathematical ability
•Awareness and consciousness
•Musicality
•Artistic appreciation and creativity
•Literary appreciation
•Conﬁdence and self-esteem
•Healthy pleasures
•Mental energy
•Ability to concentrate
•Abstract thinking
•Longevity
•Social skills
⁶¹The items in the list need not be ﬁnal goods. Characteristics that are mere means to more
fundamental goods can be included. For example, even if one thinks that musicality or musical
appreciation is not intrinsically good, one can still include them in the list if one believes that they
tend—as a matter of empirical fact—to promote well-being (for example, by creating opportunitiesfor enjoyment).
    395
To illustrate the idea, take mathematical ability. Suppose that we believe
that having greater mathematical ability would tend to make our lives go
better—perhaps because it would give us competitive advantages in the
job market, perhaps because appreciating mathematical beauty is a value in
itself, or perhaps because we believe that mathematical ability is linked to
other abilities that would increase our well-being. We then pose the EOC:
Why has evolution not already endowed us with more mathematical abilitythan we have?
It is possible that answers to this EOC may be found in the other
categories we discuss in this chapter (changed tradeoffs or evolutionary
restrictions). Yet suppose that is not so. We may then appeal to an answer
in the value discordance category. Even if greater mathematical capacity
would have been maladaptive in the EEA and even if it would still be
maladaptive today, it may nevertheless be good for us, because the good
for humans is different from what maximizes our ﬁtness.
But we are not yet done. What the evolution heuristic teaches us in
this case is that we must expect that the intervention will have some
effect that reduces ﬁtness. If we cannot form any plausible idea of what
sort of effect the intervention might produce that would reduce ﬁtness,
then we must suspect that the intervention will have important effects thatwe have not understood. That should give us pause. A ﬁtness-reducing
effect that we have not anticipated might be something very bad, such as a
serious medical side-effect. The EOC hoists a warning ﬂag. If, however, we
can give a plausible account of why the proposed intervention to increase
mathematical ability would reduce ﬁtness, and yet we judge this ﬁtness-reducing
effect as desirable or at least worth enduring for the sake of the beneﬁt ,t h e nw e
have met the EOC.
This does not guarantee that the enhancement will succeed. It is still
possible that the intervention will fail to produce the desired result or that
it would have some unforeseen side-effect. There might be more than one
sufﬁcient reason why evolution did not already make this intervention to
enhance mathematical ability. But once we have identiﬁed at least one
sufﬁcient reason, the warning ﬂag raised by the EOC comes down. Wehave shown that one potential reason for thinking that the enhancement
will fail (the ‘‘wisdom of nature’’ reason) does not apply to the present case.
As an example, evolution has not optimized us for happiness and has
instead led to a number of adaptations that cause psychological distress and
396     
frustration. ⁶²The ‘‘hedonic-treadmill’’ causes us quickly to adapt to positive
experiences and to seek more, as goods we have gained become taken for
granted as a new status quo. ⁶³Sexual jealousy, romantic heartaches, status
envy, competitiveness, anxiety, bor edom, sadness and despair may have
been essential for survival and reproductive success in the EEA, but they take
a toll in terms of human suffering and may substantially reduce our well-
being. An intervention that caused an upward shift in hedonic set-point, orthat down-regulated some of these negative emotions, would hence meet
the EOC: we can see why the effect would have been maladaptive in the
EEA, and yet believe that we would beneﬁt from these effects because of
a discordance between inclusive ﬁtness and individual well-being.
3.3. Good for society
Many characteristics that promote individual well-being also promote the
social good, but the two lists are unlikely to be identical. Table 2lists some
candidate traits that might contribute to the good of society.
As with the list for individual well-being, this one is for illustration only.
One could create alternative lists for various related questions, such as
traits that are good for humanity as a whole, or for sentient life, or for
Table 2. Some traits that may promote the social good
•Extended altruism
•Conscientiousness and honesty
•Modesty and self-deprecation
•Originality, inventiveness, and independent thinking
•Civil courage
•Knowledge and good judgment about public affairs
•Empathy and compassion
•Nurturing emotions and caring behavior
•Just admiration and appreciation
•Self-control, ability to control violent impulses
•Strong sense of fairness
•Lack of racial prejudice
•Lack of tendency to abuse drugs
•Taking joy in others’ successes and ﬂourishing
•Useful forms of economic productivity
•Healthy longevity
⁶²Buss 2000 . ⁶³Diener, Suh, Lucas and Smith 1999 .
    397
a particular community, or traits that speciﬁcally help us become better
moral agents. While the lists may overlap, they will likely disagree about
some characteristics or their relative importance. The evolution heuristic
can be applied using any such list as input.
To use such a list with the EOC, we proceed in the same way as with
the ‘‘good for the individual’’ source of value discordance. For example,
we might have a drug that appears to make those who take it morecompassionate. This might seem like a good thing, but why has evolution
not already made us more compassionate? Presumably, evolution could
easily have produced an endogenous substance with similar effects to the
drug; so the likely explanation is that a higher level of compassionateness
would not have increased inclusive ﬁtness in the EEA. We may press on and
askwhyit is that greater compassionateness would have been maladaptive
in the EEA. One may surmise that such a trait would have been associated
with evolutionary downsides—such as reduced ability credibly to threaten
savage retaliation, a tendency to spare the lives of enemies allowing them
to come back another day and reverse their defeat, an increased propensity
to offer help to those in need beyond what is useful for reciprocity and
social acceptance, and so forth. But these very effects, which would have
made heightened compassionateness maladaptive for an individual in theEEA, are precisely the kinds of effects which we might believe would be
beneﬁcial for the common good today. We do not have to assume that
the relevant trade-offs have changed since the EEA. Even in the EEA, it
might have had net good effects for a local population of hunter-gatherers
if one person was born with a mutation causing an unusually high level of
compassionateness, even though that individual himself might have suffered
a ﬁtness penalty. If we accept these premises, then the hypothetical drug
that increases compassionateness would pass the EOC. It would be a case
where we have reason to think that the wisdom of nature has not achieved
what would be best for society and that we could feasibly do better.
4. Evolutionary restrictions
4.1. General remarks on evolutionary restrictions
The ﬁnal category of answers to the EOC focuses on the fact that there are
certain limitations in what evolution can do. Using the ‘‘great engineer’’
398     
metaphor, we may say that we can hope to achieve certain things with our
ham-handed tinkering that stumped Evolution, because we have access to
tools, materials, and techniques that the great ingenious engineer lacked.
Metaphors aside, we can identify several restrictions of evolution’s ability
to achieve ﬁtness-maximizing phenotypes even in the EEA. These are
important, because in some cases they will indicate clear limitations in the
‘‘wisdom of nature’’, and a fortiori cases where there is room for potentiallyeasy improvements. At a high level of abstraction, we can divide these
restrictions into three classes:
•Fundamental inability : evolution is fundamentally incapable of produ-
cing a trait A.
•Entrapment in local optimum : evolution is stuck in a local optimum that
excludes trait A.
•Evolutionary lag : evolution of trait Atakes so many generations that
there has not yet been enough time for it to develop.
These three classes, which are discussed in more detail in the following
three subsections, are not sharply separate. For example, one reason why
a trait may take a vast number of generations to develop is that it requires
escaping from one or more local optima. And given truly astronomical
time scales, even some traits that we shall regard as fundamentally beyond
evolution’s reach might conceivably have evolved. However, the three
classes are distinct enough to deserve individualized attention.
4.2. Fundamental inability
Biology is limited in what it can build. DNA can only code for proteins,
which have to act on moieties in a water-based cellular environment usingthe relatively weak chemical forces that a protein can muster. This makes
it very unlikely that any terrestrial organism could produce diamond, for
instance, since the synthesis of diamondoid structures requires signiﬁcant
energy. ⁶⁴And while bacteria can produce microscopic metal crystals, ⁶⁵
there is no way to unite them into contiguous metal. Hence evolution
⁶⁴Adding a carbon dimer to a diamond surface using a nanotechnological tool would take more than
6.1eV (Merkle and Freitas 2003 ), about 20times more energy than is released by the ATP hydrolysis
that powers most enzymatic actions.
⁶⁵Klaus, Joerger, Olsson and Granqvist 1999 .
    399
cannot achieve diamond tooth enamel or a titanium skeleton, even if these
traits would have improved ﬁtness.
Examples can be multiplied. It is unlikely that evolution could have
evolved high-performance silicon chips to augment neural computation,
even though such augmentations might have provided important beneﬁts. A
theoretical design of artiﬁcial red blood cells has been published, calculating
the performance of a potentially feasible physical structure for transportingoxygen and carbon dioxide in the blood. ⁶⁶This design, which is not limited
by the materials and pressures that can be achieved using biology, would
enable performance far outside the range of natural red blood cells.
Radical departures from nature are apt to raise a host of separate questions
regarding biocompatibility and functional integration with evolved systems.
But at least there is no mystery as to why we would not already have evolved
these enhancements even if they would have increased inclusive ﬁtness in
the EEA.
Enhancements that evolution is fundamentally incapable of producing
can therefore meet the EOC. When invoking ‘‘fundamental inability’’, it
is important to determine that the inability does not pertain merely to the
speciﬁc means one intends to use to effect the enhancement. If evolution
would have been able to employ some different means to achieve thesame effect, the challenge would remain to explain why evolution has not
achieved the enhancement using that alternative route.
4.3. Entrapment in local optimum
Evolution sometimes gets stuck on solutions that are locally but not globally
optimal. A locally optimal solution is one where any small change wouldmake the solution worse, even if some big changes might make it better.
Being trapped in a local optimum is especially likely to account for failure
to evolve polygenic traits that are adaptive only once fully developed and
incur a ﬁtness penalty in their intermediary stages of evolution. In some
cases, the evolution of such traits may require an improbable coincidence
of several simultaneous mutations that might simply not have occurred
among our ﬁnite number of ancestors. A crafty genetic engineer may be
able to solve some of the problems that were intractable to blind evolution.
⁶⁶Freitas 1998 .
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A human engineer can think backwards, starting with a goal in mind,
working out what genetic modiﬁcations are necessary for its attainment.
The human appendix, a vestigial remnant of the caecum in other
mammals, whilst having some limited immunological function, ⁶⁷easily
becomes infected. In the natural state appendicitis is a life-threatening
condition, and is especially likely to occur at a young age. There is also
evidence that surgical removal of the appendix reduces the risk of ulcerativecolitis. ⁶⁸It appears that removal of the appendix would have increased ﬁtness
in the EEA. However, a smaller appendix increases the risk of appendicitis.
Carriers of genes predisposing for small appendices have higher risks of
appendicitis than non-carriers, and, presumably, lower ﬁtness. ⁶⁹Therefore,
unless evolution could ﬁnd a way of doing away with the appendix entirely
in one fell swoop, it might be unable to get rid of the organ; whence it
remains. An intervention that safely and conveniently removed it might be
an enhancement, increasing both ﬁtness and quality of life.
Another source of evolutionary lock-in is antagonistic pleiotropy, refer-
ring to a situation in which a gene affects multiple traits in both beneﬁcial
and harmful ways. If one trait is strongly ﬁtness-increasing and the other
mildly ﬁtness-decreasing, the overall effect is positive selection for the
gene. ⁷⁰One example is the ε4allele of apolipoprotein E. Having one or
two copies of the allele increases the risk of Alzheimer disease in middle age
but lowers the incidence of childhood diarrhea and may protect cognitive
development. ⁷¹Antagonistic pleiotropy has also been discussed in relation
to theories of ageing. The local optimum here is to retain the genes in
question, but the global optimum would be to eliminate the antagonistic
pleiotropy by evolving genes that speciﬁcally produced the beneﬁcial traits
without detrimental effects on other traits. Over longer timescales, evolu-
tion usually gets around antagonistic pleiotropy, for example by evolving
modiﬁer genes that counteract the negative effects, ⁷²but such developments
can take a long time and in the meanwhile a species remains trapped in a
local optimum.
⁶⁷Fisher 2000 .
⁶⁸Koutroubakis and Vlachonikolis 2000 ; Andersson, Olaison, Tysk and Ekbom 2001 .
⁶⁹Nesse and Williams 1998 .
⁷⁰Leroi, Bartke, De Benedictis, Franceschi, Gartner, Gonos, Fedei, Kivisild, Lee, Kartaf-Ozer,
Schumacher, Sikora, Slagboom, Tatar, Yashin, Vijg and Zwaan 2005 .
⁷¹Oria, Patrick, Zhang, Lorntz, Costa, Brito, Barrett, Lima and Guerrant 2005 .
⁷²Hammerstein 1996 .
    401
Yet another way in which evolution can get locked into a suboptimal state
is exempliﬁed by the phenomenon of heterozygote advantage. This refers
to the common situation where individuals who are heterozygous for a
particular gene (i.e. have two different alleles of that gene) have an advantage
over homozygote individuals (who have two identical copies of the gene).
Heterozygote advantage is responsible for many cases of potentially harmful
genes being maintained at a ﬁnite frequency in a population.
The classic example of heterozygote advantage is sickle-cell gene, where
homozygote individuals suffer anemia while heterozygote individuals bene-
ﬁt from improved malaria resistance. ⁷³Heterozygotes have greater ﬁtness
than both types of homozygote (those lacking the sickle-cell allele and
those having two copies of it). Balancing selection preserves the sickle-cell
gene in populations (at a frequency that varies geographically with the
prevalence of malaria). The ‘‘optimum’’ that evolution selects is one in
which, by chance, some individuals will be born homozygous for the gene,
resulting in sickle-cell anemia, a potentially fatal blood disease. The ‘‘ideal
optimum’’—everybody being heterozygous for the gene—is unattainable
by natural selection because of Mendelian inheritance, which gives each
child born to heterozygote parents a 25per cent chance of being born
homozygous for the sickle-cell allele.
Heterozygote advantage suggests an obvious enhancement opportunity.
If possible, the variant allele could be removed and its gene product
administered as medication. Alternatively, genetic screening could be used
to guarantee heterozygosity, enabling us to reach the ideal optimum that
eluded natural selection.
The phenomenon of heterozygote advantage points to potential
enhancements beyond reducing susceptibility to diseases such as malaria
and sickle-cell anemia. For instance, there is some indirect evidence that
at least Type I Gaucher’s Disease (and possibly other sphingolipid storage
diseases) is linked to improved cognition, given the signiﬁcantly higher
proportion of sufferers in occupations correlated with high IQ. ⁷⁴This, and
other circumstantial evidence, is used by the authors of the cited study
to argue that heterozygote advantage can explain the high IQ test scoresand the high prevalence of Type I Gaucher’s Disease among Ashkenazi
⁷³Allison 1954 ; Cavalli-Sforza and Bodmer 1999 .
⁷⁴Cochran, Hardy and Harpending 2006 .
402     
Jews. Should this prediction be borne out by ﬁnding an IQ advantage for
heterozygote carriers of the diseases, it would suggest that screening to
promote heterozygosity, or genetic interventions to induce it, would be
viable forms of cognition enhancement that meet the EOC.
One other kind of evolutionary entrapment is worth noting here, that
of an evolutionarily stable strategy (ESS), ‘‘a strategy such that, if all the
members of a population adopt it, no mutant strategy can invade’’. ⁷⁵One
way in which a species can become trapped in an ESS is through sexual
selection. In order to be successful at wooing peahens, peacocks have
to produce extravagant tails which serve to advertise the male’s genetic
quality. Only healthy peacocks can afford to produce and carry top-notch
tails. It is adaptive for peahens to prefer to mate with peacocks that sport
an impressive tail; and given this fact, it is also adaptive for peacocks to
invest heavily in their plumage. It is likely that the species would have
been better off if it had evolved some less costly way for males to signal
ﬁtness. Yet no individual peacock or peahen is able to defect from the
ESS without thereby removing themselves from the gene pool. If there
had been a United Nations of the peafowl, through which the birds
could have adopted a coordinated millennium plan to overcome their
species’ vanity, the peacocks would surely soon be wearing a more casualoutﬁt.
The concept of an ESS can be generalized to that of an evolutionarily
stable state. A population is said to be in an evolutionarily stable state
if its genetic composition is restored by selection after a disturbance,
provided the disturbance is not too large. ⁷⁶Such a population can be
genetically monomorphic or polymorphic. Thus, while ESS refers to a
speciﬁc strategy that is stable if everybody adopts it, an evolutionary stable
state can encompass a set of strategies whose distribution is stable under
small perturbations. It has been suggested that the human population has
been in a stable state in the EEA with regard to sociopathy, which can be
seen as a defector strategy which can prosper when it is rare but becomes
maladaptive when it is more common. ⁷⁷
Another way in which evolution can fail to produce solutions that
are ﬁtness-maximizing for organisms is intragenomic conﬂict, in which
phenomena such as meiotic drive, transposons, homing endonuclease
⁷⁵Smith 1982 . ⁷⁶Ibid. ⁷⁷Mealey 1995 .
    403
genes, B-chromosomes, and plasmids result from natural selection among
lower-level units such as individual genes. ⁷⁸In cases where we can identify
intragenomic conﬂict as responsible for a suboptimal outcome, there
is an opportunity for enhancement that can meet the EOC (provided
we have the technological means to make the requisite interventions).
Genes or traits that would not have evolved, or which would not have
been stable against intragenomic competition, could be inserted, possiblysupported by interventions removing some of the competing genetic
elements.
4.4. Evolutionary lag
Evolution takes time—often, a long time. If conditions change rapidly,
the genome will lag. Given that conditions for humanoid ancestors werequite variable—due to migration into new regions, climate change, social
dynamics, advances in tool use, and adaptation in pathogens, parasites,
predators, and prey—our species has never been perfectly adapted to
its environment. Evolution is running up ﬁtness slopes, but when the
ﬁtness landscape keeps changing under its feet, it may never reach a
peak. Even if beneﬁcial alleles or allele combinations exist, they may
not have had the time to diffuse across human populations. For some
proposed enhancements, evolutionary lag can therefore provide an answer
to the EOC.
This source of answers to the EOC is related to the changed tradeoffs
category, but with the difference that here we are focusing on ways
in which even during the EEA we were not perfectly adapted to our
environment. Even if we set aside the dramatic ways in which resourcesand demands have changed since the introduction of agriculture, there
may still be instances of earlier evolutionary lags that have not yet been
truncated and which may point to opportunities for enhancement.
There are many factors limiting the speed of evolution. ⁷⁹Some are
inherent in the process itself, such as the mutation rate, the need for
sufﬁcient genetic diversity, and the constraint that selection can only
encode a few bits into the genome per generation. ⁸⁰A recessive beneﬁcial
mutation will spread to an appreciable fraction of a ﬁxed well-mixed
population in time inversely proportional to its selective advantage. For
⁷⁸Burt and Trivers 2006 . ⁷⁹Barton and Partridge 2000 . ⁸⁰Worden 1995 .
404     
example, if the mutation gives a 0.1per cent increase in ﬁtness, it will
take 9,200generations ( 230,000years assuming 25years per generation) to
reach 50per cent of the population from a starting level of 0.01per cent.
For a 10per cent ﬁtness-advantage, just 92generations ( 2,300years) are
needed. ⁸¹Population structure and especially low-population bottlenecks
can accelerate the spread signiﬁcantly.
In nature, the strength of selection for a trait is generally quite weak. A
review of published studies ⁸²found the distribution of selection strengths
across species to be exponential, with a small median magnitude: for most
traits and in most systems directional selection is fairly weak. Selection via
survival appears to be weaker than selection through mating success, making
sexual selection a big factor. Quadratic selection gradients, indicating
the ‘‘sharpness’’ of ﬁtness peaks, were also found to be exponentially
distributed and with small median. This implies that stabilizing selection
(reducing genetic diversity once a population has reached a local ﬁtness
peak) is often fairly weak. Indirect selection (where trait ﬁtness depends
on another correlated trait) also appears to be playing only a minor
role.⁸³These results suggest that beneﬁcial new traits are likely to spread
slowly.
A population living in a heterogeneous or changeable environment may
not be able to converge on a single ﬁtness peak but will be spread out
around it. This might reduce extinction risks for the lineage, since there
will always be some individuals that are well adapted if the conditions
change and the lineage will survive more easily than if a less dispersed
population had to ascend the current gradient towards the top through a
region of low survivability.
It is possible to detect empirically the presence of genetic variations
under positive ﬁtness pressure through their signatures. ⁸⁴These signatures
range from multimillion-year timescale changes in gene sequence (mostly
useful to point out ongoing or recurrent selection), to changes in genetic
diversity caused by the rapid spread of a beneﬁcial mutation in the past
250,000years, to the differences between human populations which can
⁸¹Cavalli-Sforza and Bodmer 1999 .
⁸²Hoekstra, Hoekstra, Berrigan, Vignieri, Hoang, Hill, Beerli and Kingsolver 2001 .
⁸³Ibid.
⁸⁴Sabeti, Schaffner, Fry, Lohmueller, Varilly, Shamov sky, Palma, Mikkelsen, Altshuler and Lander
2006 .
    405
indicate genetic selection over the last 50,000–75,000years. Such long-
term selection evidence is mainly useful for understanding the selection
pressures in the EEA.
There is evidence for recent positive selection in humans. ⁸⁵Some of
it may be in response to climate variations, producing a wide range of
variation in salt-regulating genes in populations far from the equator. ⁸⁶
Genes involved in brain development have also been shown to have beenunder strong positive selection with new variants emerging over the last
37,000years ⁸⁷and5,800years. ⁸⁸
There is evidence that genes related to the brain have evolved more
quickly in the human lineage than in other primates and rodents. ⁸⁹The
rapid growth of the brain in the human lineage also suggests that its size
must be controlled by relatively simple genetic mechanisms. ⁹⁰Despite this,
it should be noted that the selection differential per generation for human
brain weight during the Pleistocene was only 0.0004 per generation: ⁹¹even
under fast evolution brain size was limited by tradeoffs.
If we ﬁnd a gene that has a desirable effect, and that evolved recently
and has not yet spread far despite showing evidence of positive selection,
interventions that insert it into the genome or mimic its effects would
likely meet the EOC. A simple example would be lactose tolerance. Whiledevelopment of lactose intolerance is adaptive for mammals since it makes
weaning easier, dairy products have stimulated selection for lactase in
humans over the last 5,000–10,000years. ⁹²This is so recent that there has
not been time for the trait to diffuse to all human populations. (Populations
that have domesticated cattle but do not have lactose tolerance instead
make use of fermented milk or cheese.) Taking lactase pills enables lactose-
intolerant people to digest lactose, widening the range of food they can
enjoy. This enhancement clearly passes the EOC.
⁸⁵Voight, Kudaravalli, Wen and Pritchard 2006 .
⁸⁶Thompson, Kuttab-Boulos, Witonsky, Yang, Roe and Di Rienzo 2004 .
⁸⁷Evans, Gilbert, Mekel-Bobrov, Vallender, And erson, Vaez-Azizi, Tishkoff, Hudson and Lahn
2005 .
⁸⁸Mekel-Bobrov, Gilbert, Evans, Vallender, Anderson, Hudson, Tishkoff and Lahn 2005 .
⁸⁹Dorus, Vallender, Evans, Anderson, Gilb ert, Mahowald, Wyckoff, Malcom and Lahn 2004 .
⁹⁰Roth and Dicke 2005 .
⁹¹Cavalli-Sforza and Bodmer 1999 ,692.
⁹²Bersaglieri, Sabeti, Patterson, Vanderploeg, Schaffner, Drake, Rhodes, Reich and Hirschhorn
2004 ; Tishkoff, Reed, Ranciaro, Voight, Babbitt, Silverman, Powell, Mortensen, Hirbo, Osman,
Ibrahim, Omar, Lema, Nyambo, Ghori, Bumpstead, Pritchard, Wray and Deloukas 2007 .
406     
5. Discussion
The evolution heuristic instructs us to consider, for an apparently attractive
enhancement, why we have not already evolved the intended trait ifit is really such a good idea. We called this question the Evolutionary
Optimality Challenge, and we have described three broad categories of
possible answers, and given some examples of particular enhancements
for which it is possible to meet the EOC, and which, therefore, seem
comparatively promising as intervention targets that may be feasible in the
relatively near term and which may have on balance beneﬁcial effects.
In general, when we pose the EOC for some particular proposed
enhancement, we might discover one of several things:
1. Current ignorance prevents us from forming any plausible idea about
the evolutionary factors at play.
2. We come up with a plausible idea about the relevant evolutionary
factors, and this reveals that the proposed modiﬁcation would likely not
be a net beneﬁt.
3. We come up with a plausible idea about the relevant evolutionary
factors, and this reveals why we would not already have evolved to have
the enhanced capacity even if it would be a net beneﬁt.
4. We come up with several plausible but mutually inconsistent ideas about
the relevant evolutionary factors.
The ﬁrst possibility means that we have no clear idea about why, from
a phylogenetic perspective, the trait that is the target of the proposed
enhancement is the way it is. This should give us pause. If we do not
understand why a very complex evolved system has a certain property,
there is a considerable risk that something will go wrong if we try to modify
it. The case might be one of those where nature does know best. Like an
over-ambitious tinkerer with merely superﬁcial understanding of what he
is doing while he is making changes to the design of a master craftsman,
the potential for damage is considerable and the chances of producing an
all-things-considered improvement are small.
We are not claiming that it is always inadvisable to try an intervention
when we have no adequate understanding of the subsystem we intend
to enhance. We might have other sources of evidence that afford us
    407
sufﬁcient assurance that the intervention will work and will not cause
unacceptable side-effects, even without understanding the evolutionary
functions involved. For example, we might have used the intervention
many times before and found that it works well. Alternatively, we might
have evidence from a closely analogous subsystem, such as an animal
model, that suggests that the intervention should work in humans too. In
such cases, the evolution heuristic delivers only a weak recommendation:that absent any good answer to the EOC, we should proceed only with
great caution. In particular, we should be alert to the possibility that the
proposed intervention will turn out to have signiﬁcant (but perhaps subtle)
side-effects.
The second possibility is that we succeed in developing a plausible
understanding of the pertinent evolutionary factors, and, having done so,
we ﬁnd our initial hopes about the proposed modiﬁcation undermined.
None of the three categories we have described yields a satisfactory answer
to the EOC: the relevant tradeoffs have not changed since the EOC, there
is no relevant value discordance, and no evolutionary restriction would
have prevented the modiﬁcation from already having evolved by now.
In this case we have strong reason for thinking that the enhancement
intervention will fail or backﬁre. If we proceed, the wisdom of nature willbite us.
The fourth possibility is that we come up with two or more plausible
but incompatible evolutionary accounts of the evolutionary factors at play.
In this case, we can consider the implications of each of the different
evolutionary accounts separately according to the above criteria. If all yield
green lights, we are encouraged to proceed. If some of the evolutionary
accounts yield green lights but others yield red lights, then we face a
situation of uncertainty. We can use standard decision-theory to determine
how to proceed—we can take a gamble if we feel that the balance of
probabilities sufﬁciently favor the green lights; if not, we can attempt to
acquire more information in order to reduce the uncertainty, or forgo the
potential enhancement and try something else.
The evolution heuristic is not a rival method to the more obvious way of
determining whether some enhancement intervention works: testing it in
well-designed clinical trials. Instead, the heuristic is complementary. It helps
us ask some useful questions. By posing the EOC, and carefully searching for
and evaluating possible answers in each of the three categories we described,
408     
we can (a) identify promising candidate enhancement interventions, to be
explored further in laboratory and clinical studies, and (b) better evaluate
the likelihood that some intervention which has shown seemingly positive
results in clinical studies will actually work as advertised and will not have
unacceptable side-effects of a hidden, subtle, or long-term nature.
6. Conclusion
There is a widespread belief in some kind of ‘‘wisdom of nature’’. Many
people prefer ‘‘natural’’ remedies, ‘‘natural’’ food supplements, and ‘‘nat-
ural’’ ways of improving human capacities such as training, diet, and
grooming. ‘‘Unnatural’’ interventions are often viewed with suspicion, and
this attitude seems to be especially pronounced in relation to unnatural ways
of enhancing human capacities, which are viewed as unwise, short-sighted,
and hubristic. We believe that such attitudes also exert an inﬂuence on
beliefs about the kind of matters that arise in bioethical discussions of
human enhancement.
While it is tempting to dismiss intuitions about the wisdom of nature as
vulgar prejudice, we have suggested that these intuitions contain a grain of
truth, especially as they pertain to human enhancement. We have attempted
to explicate this grain of truth as the Evolutionary Optimality Challenge.
After posing this challenge, the evolution heuristic instructs us to examine
three broad categories of potential ways of meeting the challenge: changed
tradeoffs, value discordance, and evolutionary restrictions. These categories
correspond to systematic limitations in the wisdom of nature idea. For
some potential enhancement interventions, the challenge can be met with
an answer from one of these categories; for other potential interventions,
the challenge cannot be met. The latter interventions merit suspicion, and
attempting them may indeed be unwise, short-sighted, and hubristic. The
former interventions, in contrast, do not defy the wisdom of nature and
have a better chance of working.
By understanding both the sense in which there is validity in the idea
that nature is wise and the limits beyond which the idea ceases to be valid,
we are in a better position to identify promising human enhancements andto evaluate the risk–beneﬁt ratio of extant enhancements. If we are right in
supposing that intuitions about the wisdom of nature exert an inarticulate
    409
inﬂuence on opinion in contemporary bioethics of human enhancement,
then the evolution heuristic—while primarily a method for addressing
empirical questions—may also help to inform our assessments of more
normatively loaded items of dispute. ⁹³
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