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Defining the human embryo: A way with words?

5 July 2006
By Professor Martin H Johnson
Professor of Reproductive Sciences, University of Cambridge
Appeared in BioNews 366
In February this year, the Australian National Health and Medical Research Council (1) published a discussion paper entitled: 'Human Embryo - A biological definition'. This publication provides an authoritative and comprehensive summary of the scientific arguments and experiments that bear on our understanding of what a human embryo is and is not. The paper clearly documents the difficulties that scientists have had when failing to reach agreement on a definition, but nonetheless, and perhaps unwisely, presses on to produce one. Why? Ever since the first successful IVF (2), the human embryo has been problematic, not least because, despite scientific disagreement on a definition, many people seem to want one. In Australia, a commission reviewing national legislation on human embryo research and cloning headed by Justice Lockhart (3) explicitly stated: ' is essential that the terminology used in the legislation is biologically accurate, clearly understandable by all stakeholders, and unambiguous to regulators, scientists and the public'. The NHMRC responded to this judicial statement with the following definition:

'A human embryo is a discrete entity that has arisen from either:

(a) the first mitotic division when fertilisation of a human oocyte (egg) by a human sperm is complete; or

(b) any other process that initiates organised development of a biological entity with a human nuclear genome or altered nuclear genome that has the potential to develop up to, or beyond, the stage at which the primitive streak appears;

(c) and has not yet reached eight weeks of development since the first mitotic division'.

Readers will decide for themselves whether this definition will prove any more agreeable, durable or useful than previous ones. However, I suspect that even this valiant attempt to forge consensus will not succeed. There are various reasons for my pessimism, which are discussed in detail in a recent paper (4), but at their heart are two core considerations. First, just because politicians, lawyers, regulators, philosophers, theologians or the public want a definition from scientists, it doesn't automatically follow that scientists should give one. One must consider first whether the request is an appropriate one to make? I would argue that it is not.

Development is a continuous process, but the question assumes the embryo to be categorical - to have a beginning and an end. A scientist would not answer the question: 'Tell me exactly when humankind came into existence?' - the sort of question a creationist might ask. So why should a scientist answer an inappropriate question about when an embryo first exists (and ceases to)? The second consideration arises from this latter rhetorical question, a possible answer to which might be: 'Because by agreeing a definition, I can at best tailor it to the purposes for which I want to be able to use the embryo and at worst, I know where I stand with regard to the law'. This answer may seem somewhat cynical, but, as Christine Hauskeller (5) has shown using case studies in Germany and the UK, that is effectively what has been happening, whether consciously or otherwise, in the scientific-legal discourse on embryo definition since the 1980s. Moreover, acquiescing to a definition hasn't even achieved the hoped for objective of legal certainty (4, 5)!  

The reason for this extra-ordinary dance of words is due, at least in part, to the fact that the early legislative responses to fertilisation of human eggs in vitro exaggerated the protection of the embryo at the expense of the interests of other parties, especially of the parents and intended children. Pressure groups on both sides of the debate tended to conflate the embryo with babies - either 'genetically engineered monsters' or 'healthy bouncing ones'.  In the process, the embryo itself was pushed into the limelight as the central player and its prominence distorted legal thinking. Perhaps it is time to relax this embryonic grip and bring proportionality to the political and legal approaches to embryo regulation?

As a stimulus to discussion, I have explored (4) a reframed legislative approach to the regulation of assisted reproductive technology (ART) that attempts (i) to align more closely the legal and biological understandings of the earliest stages of human development; (ii) to place the legislative focus on objective, intent and measurable outcome rather than process; and in doing so (iii) to disentangle legally and conceptually the status of the embryo from that of the potential child. In this exploration, the requirement for human embryo definition evaporates. So can we agree: 'Away with words of definition and let the words say what they mean - truly a way with words?'

Biology and Philosophy 20, 815-835 (2005)
5) Hauskeller C: Science in touch: functions of biomedical terminology |  20 May 2022
Human Reproduction (2006)
4) Johnson MH: Escaping the tyranny of the embryo? A new approach to ART regulation based on UK and Australian experiences |  20 May 2022
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