The empirical embryo

Laws cannot produce scientific facts, and yet lawmakers, regulators and judges commonly attempt to do so when defining terms. Inattentive to the methods of Francis Bacon (who was Lord Chancellor of England in addition to being a pioneer of the scientific method), their efforts are doomed.

The special status of the human embryo, the Warnock Report proposed, should be recognised in law. However, defining 'embryo' has proved oddly fraught. With the advent of human stem-cell-based embryo models (SCBEMs), some are calling for a more meaningful legal definition of the embryo under the Human Fertilisation and Embryology (HFE) Act 1990. But far from needing additional detail, today's definition would be better curtailed.

In its original definition in the HFE Act 1990, Parliament declared 'embryos' to be products of fertilisation, thereby creating an unnecessary precondition of embryodom. Parliament's statutory hypothesis was inevitably disproved by cell nuclear replacement, necessitating court intervention to vanish away Parliament's unequivocal words (see BioNews 199). Eighteen years after enacting those words, Parliament deleted them (see BioNews 484).

It's not a lone example. Although European and UK patent statutes wisely avoid defining 'human embryo' (they also avoid defining 'invention'), the Court of Justice of the EU – having ruled the term to mean an organism 'commencing the process of development of a human being' – declared that for this reason, parthenotes are 'human embryos' and consequently unpatentable (see BioNews 630, 684 and 686).

The Court had assumed that parthenotes could develop into human beings, oblivious to the necessity of parental imprinting for onward development, and set its erroneous conjecture in legal concrete so that – yet again – law-made science was undermined by the inconvenience of empirical fact. This required exorbitant redlining, in this case by different judges of the same Court, who conceded that parthenotes are not 'human embryos' because – unlike human embryos – they lack the 'inherent capacity of developing into a human being' (see BioNews 763, 765 and 785). If, however, a parthenote's genes were imprinted, then that parthenote might be a 'human embryo'.

Correction is not inevitable. Australia's Embryo Research Licensing Committee recently decreed SCBEMs to be 'embryos'. Consequently, those who use such (non-) embryos without an embryo licence, or who intentionally develop them in vitro beyond 14 days of (imaginary) fertilisation, face long-term imprisonment. No matter that these 'embryos' cannot develop into human beings, nor (in the vast majority of cases) do they even have 'the potential to develop up to, or beyond, the stage at which the primitive streak appears', in the words of Australia's statutory definition. Thanks to a committee, Australia SCBEMs now gastrulate in law, if not in fact.

This isn't to say that Australia's 'embryo' definition is unscientific. Far from it – it positively sparkles with expressions such as 'mitotic', 'oocyte', 'nuclear genome', and 'potential to develop... the primitive streak'. It's striking, however, that all of these are (among the) characteristics that an embryologist would recognise anyway, by empirical assessment of a live human embryo formed by the union of egg and sperm. In which case, why bother?

Still, we might admire the scientifically 'refined' legal definition of the embryo proposed last year (see BioNews 1203). If dubbing an embryo test a SCBEM 'Turing test' appears grandiloquent, it nevertheless highlights the fact that empirical comparison with the human benchmark is fundamental. The inclusion of extraembryonic and uterine functions seems especially pertinent, the accent on function capturing models that substitute tissue with physicochemical cues.

However, resting the test on the unqualified 'similarity' of extraembryonic and uterine functions of nonhuman SCBEMs to those of human embryos seems incompatible with a Turing test. Among primates, only in humans, great apes and gibbons is the blastocyst pulled into and embedded by the endometrium. But at six to eight million years, the genomic gap between humans and chimpanzees is still immense, with significant differences of placentation and development. Cynomulgus monkeys provide a useful model, but the genomic gap is wider still. A human is not a crab-eating macaque. The fact that something is ethically significant does not make it a human embryo.

Viewed like this, the definition that remains in the UK Act following deletion of the fertilisation gaffe appears more than adequate – an 'embryo' means a 'live human embryo', irrespective of how it was made. Apart from excluding non-living and non-human embryos, an embryo is just an embryo. It's simply a question of fact, not law. No definitional issue arises outside the research provisions of the Act, and research is precisely directed to generating empirical data about what embryos are and what they are not. Data, not words, provide the best definition of a human embryo.

Those exasperated by the UK's circular definition should recall that in his Dictionary, Samuel Johnson defined a cow as the female of a bull, and a bull as the male of a cow. He wasn't being facetious. It's true that a cow is a mammal with four legs, horns and a tail, but so is a goat. Dr Johnson's definition is preferable simply because, to paraphrase Lord Millet in the leading judgment on the meaning of 'embryo', it assumes that the reader knows what a bull or cow is.

In the preface to his Dictionary, Johnson warned lawyers that words are 'too volatile and subtile for legal restraints'. Johnson's caveat is borne out by courts having to interpret old statutory expressions to reflect newer understandings, with 'bodily harm' now capturing psychological harm, and 'cruel and unusual punishment' penalties less draconian than thumb-screwing. Technical terms age particularly rapidly, with courts having to construe expressions like 'telegraph' to include telephones, and 'documents' to include tape recordings. But, defining objects of scientific research is uniquely challenging.

As research characterises defined objects such as 'embryo' in ever-greater detail, it also distinguishes objects falling outside them. Some of these objects – for example, some SCBEMs – may be ethically consequential, but the rule of law forbids construing statutory terms beyond Parliamentary intent.

This is the governance dilemma of scientific research. Drafting all-encompassing definitions invokes disproportionate regulation, but over-particular definitions miss consequential subject matter. To reconcile the principles of scientific doubt with statutory certainty, we should – in a Baconian spirit – incorporate the fewest possible presumptions into scientific definitions. The regulations in which those definitions function then require formal systems to accommodate change, a calculus for governing undefined things to the highest standards.

Such a regulatory calculus necessitates anticipation of key ethical concerns for a class of objects, delegation to a competent oversight body responsible for that class, engagement of researchers and overseers with anticipated ethical concerns and proportionate transition of jurisprudence to statute.

Julian Hitchcock is a member of the Working Group that produced the Code of Practice for the Generation and Use of Human Stem Cell-Based Embryo Models, published jointly by Cambridge Reproduction and PET.