This is the full version of my article on mitochondrial transfer, published last month in the International New York Times under the headline ‘The Three-Parent Baby’s First Step’.

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The British Parliament can be an archaic, backward-looking institution, wedded to tradition, and not known for taking a revolutionary stance. Yet its members have just made a groundbreaking decision, one that no other legislature has so far been willing to contemplate. They approved legislation that makes Britain the first country formally to allow the creation of what many call ‘three-parent babies’. Supporters say the procedure will enable women to avoid passing on certain severe and even deadly genetically inherited diseases. But many regard the new law as an unwise, even immoral, move — the first step toward the creation of ‘designer babies’. Some even see it as a new experiment in eugenics.

‘Three-parent babies’ is a sensationalized term to describe a special form of in vitro fertilization, or IVF, that is better labeled ‘mitochondrial transfer’ or ‘mitochondrial donation’. Every human cell comprises two main parts: the nucleus and the cytoplasm. The nucleus contains the DNA, the genetic code that helps shape inherited traits. The cytoplasm is the workshop of the cell, where most day-to-day functions occur. Among its constituent parts are mitochondria, tiny organelles whose job it is to provide energy. Each mitochondrion contains tiny amounts of its own DNA, some 37 genes compared with the 20,000 or so in the nucleus. (It is thought that way back in evolutionary history, a free living bacterium became trapped in a host cell, where it boosted the cell’s capacity to produce energy; over time, it evolved into an organelle, an intimate part of the cell, but retained its own DNA.)

Mitochondrial DNA plays no part in determining an individual’s inherited traits, such as those that shape appearance or talents. But if it malfunctions, it can cause terrible conditions like muscle weakness, seizures, blindness, deafness, organ failure and even death. There are more than 50 mitochondrial diseases, affecting at least one in every 8,000 children (some suggest the figure is much higher). There are currently no cures.

In mitochondrial transfer, the healthy nucleus of an egg with damaged mitochondria is transferred into the body of a healthy donor egg from which the nucleus has been removed. When that egg is fertilized, it will have its normal complement of genes from the mother and father, together with a tiny amount of mitochondrial DNA from the healthy third-party egg into which the nucleus was transferred. (The new British law also permits a more complex alternate technique, in which both eggs are first fertilized in vitro, and then the nucleus of the egg with defective mitochondria is transferred to the healthy donor egg, from which the nucleus has been removed.)

Hence the notion of a ‘three-parent baby’ — misleading though the term is. None of the socially or ethically important characteristics of the child will derive from the ‘third parent’.What makes you ‘you’ depends upon far more than your genes, of course, but insofar as genes play a role in personality or talent or physical attributes, they all derive from the nucleus. In the case of mitochondrial transfer, such genes will come, not from the woman who donated the egg with working mitochondria, but from the nucleus of the woman with faulty mitochondria and from the sperm of her partner. Those two are truly the child’s only parents.

The best analogy for mitochondrial transfer is that of an organ transplant. Transplanting healthy mitochondria is little different from transplanting a healthy kidney or heart into a person with a diseased organ — and should be no more ethically troubling.

If the term ‘three-parent baby’ does not describe the reality of the process, it does raise the spectre of scientists ‘playing God’ and of championing supposedly unnatural methods. The belief that scientists or doctors should not play God has always struck me as odd. Playing God — in the sense of interfering in the natural course of events so as to improve human lives — is precisely what doctors are required to do every day of the year. Whether transplanting naturally faulty hearts, or delivering a baby by cesarean section when natural birth may be impossible or dangerous, the very essence of medicine is to right the wrongs of nature.

Even less tenable is the claim that the process creates ‘designer babies’. A designer baby is one whose genes have been altered to change, or improve, certain characteristics. Today, we can perform in vitro screening of embryos for certain genetic defects or characteristics such as sex. But we are a long way from the kind of genetic modification implied by the notion of designer babies. Whatever the moral arguments about the desirability or otherwise of such modifications, these are irrelevant to the issue of mitochondrial transfer. There is no genetic interference or ‘redesign’.

It is true that the donor’s mitochondrial DNA will (if the child is a girl) be passed on to the next generation. That should make us cautious to ensure that no problems are passed down the generations by the process. But the need for caution does not necessarily make the process ethically problematic.

Imagine a situation in which a woman with mitochondrial abnormalities conceives naturally, rather than through mitochondrial transfer. In this case, too, mitochondrial DNA would be passed down the generation. The only difference is that future generations would inherit faulty, rather than working, DNA. Why should it be ‘ethical’ to pass on faulty DNA, but ‘unethical’ to impart healthy DNA?

The critics of mitochondrial transfer turn the ethical issues on their head. There are no reasons to regard mitochondrial transfer as unethical. There is, though, something deeply immoral about the attempt to block techniques that could alleviate the suffering of thousands of babies born every year with mitochondrial abnormalities.

The opponents like to cast the debate as one between amoral scientists, hellbent on progress at any cost, and those who seek to place scientific advancement within a moral framework. But what is moral about causing unnecessary misery by preventing medical advance? And what could be more ethical than seeking to reduce such suffering through the development of medical techniques? For once, Britain’s Parliament embraced the future and made the ethical decision.