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Question

2 | VARIE TIES O F P REC AUTIONARY
PRINCIPLES
It is difficult to offer a precise definition of the precautionary principle
as many different versions of it exist. The differences between these
versions can be radical. The precautionary principle has been conceptualized
as a rule of choice intended to help us select the best course of
action, as an epistemic rule intended to guide only our beliefs and as a
procedural requirement specifying processes that policymakers should
follow when making risky decisions.16 We treat the precautionary
principle as a rule of choice. This is consistent with how the precautionary
principle tends to be applied in the bioethics literature.17 This
is also the version of the precautionary principle that is most relevant
to the motivating question of this article; i.e. how should we weigh the
risks and benefits of human germline interventions?
Even restricting our analysis to the precautionary principle as a
rule of choice, the precautionary principle can take many different
forms. A distinction is commonly drawn between weak and strong
forms of the precautionary principle. We draw a parallel distinction
between negative and positive precautionary principles.18 This distinction
runs as follows:
Negative precautionary principle. When an activity
may cause harm we should not abstain from taking
precautionary action because we lack certainty that
the activity in question would cause harm. Positive precautionary principle. We should take
(some form of) precautionary action against activities
that may cause (some kinds of) harm.
Negative versions of the precautionary principle do not make positive
claims about when precautionary action should be taken; they merely reject
one possible reason against taking precautionary action. By contrast,
positive precautionary principles require decision‐makers to take certain
kinds of precautionary measures against certain kinds of threats. Positive
versions of the precautionary principle can range from being extremely
demanding to being extremely undemanding, depending on what kinds of
threats are thought to trigger the principle, what kinds of remedies are prescribed
and how strongly these remedies are recommended.19 Consider
the following two hypothetical positive precautionary principles:
Strong positive precautionary principle. One must
take extensive precautionary action to eliminate fully
any potential threats to human well‐being, regardless
of the costs of the precautionary action, the likelihood
that the threat would eventuate and the degree
of harm posed by the threat.
Weak positive precautionary principle. One should
consider taking some minimal precautionary actions
against catastrophic threats to human well‐being that
are highly likely to eventuate. 20
Both the above precautionary principles are positive. However,
where the first demands that extensive precautionary measures be
taken under an extremely broad range of conditions, the second
lightly recommends taking undemanding precautionary measures
against only the most serious of hazards (as we presumably already
do as a matter of course). The first positive precautionary principle
is implausibly strong, whereas the second is unhelpfully weak. It is
nonetheless possible that some moderate positive precautionary
principle may provide a useful guide to decision‐making.
Some – although not all – forms of the precautionary principle
also make explicit reference to the burden of proof.21 Such versions
of the precautionary principle generally require those advocating
potentially hazardous activities to prove that the activity is (sufficiently) safe to be allowed; the corollary is that advocates of
precautionary measures need not prove the activity is hazardous before
implementing precautionary measures. We do not specifically
address burden of proof requirements in this article. On one view,
which we find convincing, burden of proof requirements are merely
an instrumental means of achieving the precautionary principle’s underlying
normative goals – for example, to place greater weight on
avoiding some kinds of outcomes than on others.22
In what follows, we consider whether negative and positive versions
of the precautionary principle should influence how we weigh
the risks and benefits of GGE. We conclude that the precautionary
principle does have a legitimate role to play in ethical analyses of
GGE, although this role is less straightforward than many might expect.
We reach two main conclusions: that no plausible version of
the precautionary principle entails that we should reject outright the
use GGE in human reproduction and that the precautionary principle
can nonetheless help shape the developmental trajectory of GGE by
encouraging some applications over others.

Answer 1

2 | VARIATIONS OF PRECAUTIONARY PRINCIPLES

Defining the precautionary principle precisely is challenging due to its various interpretations, which can differ significantly. It can be seen as a guideline for choosing the optimal course of action, a rule influencing our beliefs, or a procedural standard that policymakers should adhere to when making decisions involving risks. In this article, we focus on the precautionary principle as a rule of choice, aligning with its typical application in bioethics. This perspective is particularly relevant to our key inquiry: how should we assess the risks and benefits of interventions in the human germline?

Even when limiting our focus to the precautionary principle as a rule of choice, it remains multifaceted. A common differentiation exists between weak and strong forms of the precautionary principle. We parallel this with negative and positive precautionary principles. This distinction is outlined as follows:

• Negative precautionary principle: We should not refrain from taking precautionary measures because we lack certainty that an activity will cause harm.

• Positive precautionary principle: We should implement some form of precautionary action against activities that could potentially cause harm.

Negative versions do not explicitly indicate when precautionary actions should be taken; they simply reject one rationale against such actions. In contrast, positive precautionary principles mandate decision-makers to adopt precautionary steps against specific threats. These positive principles can vary widely in their demands, based on the perceived threats, the recommended remedies, and the strength of these recommendations.

For instance, consider these two hypothetical positive precautionary principles:

• Strong positive precautionary principle: Extensive precautionary actions must be taken to completely eliminate any possible threats to human well-being, regardless of associated costs, the likelihood of the threat occurring, or the potential harm it may cause.

• Weak positive precautionary principle: Minimal precautionary measures should be considered against catastrophic threats to human well-being that are highly likely to happen.

Both principles are positive; however, the first advocates for extensive measures across broad conditions, while the second suggests only basic precautions against the most severe risks. The first principle is overly stringent, while the second is insufficiently demanding. Yet, it's possible that a moderate positive precautionary principle could offer a practical framework for decision-making.

Certain interpretations of the precautionary principle explicitly address the burden of proof, requiring those proposing potentially risky activities to demonstrate their safety. In such cases, proponents of precautionary measures are not obligated to show that the activity is harmful before implementing precautions. While this article does not delve into burden of proof considerations, we maintain that such requirements are tools to further the goal of the precautionary principle—namely, to prioritize the avoidance of certain negative outcomes.

Next, we analyze whether negative and positive versions of the precautionary principle should influence our evaluation of the risks and benefits of germline gene editing (GGE). We conclude that while the precautionary principle plays a valid role in the ethical considerations of GGE, its application is not as clear-cut as some might believe. Our conclusions are twofold: no reasonable version of the precautionary principle suggests that we should completely reject GGE in human reproduction, and it can still guide the development of GGE by prioritizing certain applications over others.