How worried should we be about the 'slippery slope to designer babies'?

Two recent news stories have provoked talk of 'designer babies': the government's decision to move towards allowing mitochondrial replacement therapy (MRT); and the announcement, at this month's ESHRE conference, that the first child has been born following the use of 'next-generation sequencing' (NGS). Both techniques have therapeutic goals. MRT aims to enable patients to have children free from mitochondrial disorders, many of which are fatal. NGS aims to increase success rates for IVF. So why are potentially positive developments like this greeted with talk of 'designer babies', and is such language justified?

The expression 'designer babies' is rarely defined with clarity. It evokes thoughts of parents unhealthily obsessed with their child's appearance or who want to enhance their children to create, as Heather Long puts it, 'a kind of demi-god race that will be taller, healthier [and] better-looking'. But 'designer babies' is at the same time applied much more widely to cases that have nothing to do with enhancement or with the way children look. Given this ambiguity, we should approach claims about 'designer babies' with considerable caution.

One of the main arguments lying behind people's concerns about 'designer babies' is the slippery slope. David King, talking about MRT, says: 'Once we've crossed this crucial ethical line, which says that we shouldn't create babies that have been genetically altered, it becomes very difficult to then stop when the next step is wanted and then the next step after that and we will eventually get to this future that everyone wants to avoid of designer babies.'

While Heather Long, reacting to NGS, says: 'It will likely be a progression from just wanting a child, to wanting one less likely to get certain diseases, to wanting one more likely to have traits associated with being taller or more artistic or athletic. From there, it's not too hard to imagine something akin to the Subway sandwich line where you select different traits a la carte.'

The basic idea behind the slippery slope argument is that even if X isn't itself wrong, we shouldn't accept or allow X because that would be to step onto the 'slippery slope' to Y — and Y really is wrong. Not all slippery slope arguments are defective. Some work; some don't. Whether they work depends on two questions. Is the slope as slippery as is claimed — will X inevitably lead to Y? And is Y as bad as it's made out to be?

Take MRT. The slippery slope argument is that anything short of a categorical prohibition on the genetic modification of human embryos will lead us 'down the slope' to unfettered modification ('designer babies'). Why? Because, so it's claimed, once the principle of 'no genetic modification' has been abandoned then we won't have any basis on which to object to genetic modification of any kind.

This, however, supposes that there aren't ethical principles that would allow us to draw a line between MRT and unfettered genetic modification — but there are some such principles. One is the idea that human genetic modification is permissible only when its purpose is to prevent illness. This seems plausible to many, such as those who regard using reproductive biology to avoid disease as good, but have reservations about its use for some other purposes. And a parallel principle can be found in existing UK law on embryo selection and testing, which is permitted only for a limited range of purposes, mostly to do with the health of the resultant child, or with increasing the chances of a live birth. So the possibility of operating with a principle like this, and of embedding it in law, casts doubt on this slippery slope argument. (There are of course other possible responses to this slippery slope argument. For example, it might be suggested that the distinction between mitochondrial and nucleur DNA is important, or that MRT is not really an instance of 'modification' in the relevant sense of the word.)

Then there's the question of just how bad a world containing 'designer babies' would be. Heather Long's worry seems in large part about NGS's effects on socio-economic inequality. Inequality is something we should all be concerned about, but whether it constitutes an objection specifically to MRT or NGS is far from clear.

First, concerns about unfair distribution can be raised about most new (and many old) technologies. Anything which gives the owner/user an advantage and can only be afforded by the rich can be objected to on this ground — be it smart phones, hospitals, motorways, refrigeration, or school books. Second, Long's worry about inequality seems only to apply to human enhancement, rather than 'designer babies' more widely, for parents who merely choose their children's eye and hair colours are unlikely to give them much of an advantage, especially in an age where contact lenses and dyes can achieve similar effects. Third, we can't just assume that new technologies have negative effects on social inequality. Indeed, one of the claims made for NGS is that it could make infertility treatment much cheaper by increasing success rates; it could therefore increase access to IVF for the less well-off.

How worried then should we be about the 'slippery slope to designer babies'? As I've said, we shouldn't automatically reject slippery slope arguments; some of them do work. But the ones presented so far in relation to MRT and NGS are unconvincing. This is partly because we need a clearer idea of what exactly a 'designer baby' is and what would be wrong with creating one; we need to know what's at the bottom of the 'slope' and why we should be afraid of it. And it's partly because there's reason to believe, based on other areas of policy and practice, that we're capable of distinguishing (albeit imperfectly) interventions that are genuine treatments for patients from those which merely satisfy people's trivial cosmetic preferences. Provided that we can make such distinctions then the 'slope' may not be anything like as 'slippery' as is sometimes supposed.