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Key points
- Few people realize just how powerful embryo selection will become in the near future.
- Over the past two decades, the human genome has been decoded, and genetic testing has become ubiquitous.
- We will still have sex. And we will still have children. But the link between the two will grow more tenuous.
Sex is fun because people who found it boring died without descendants.
But the link between having sex and having kids has been severed since the sexual revolution of the late 1960s. Cheap contraception allowed women to decide when to have children. Social norms also changed—abortion became easier to access in case contraception failed.
Whatever you think of these developments, contraception and abortion have led many people see sex as an activity we do for pleasure (or for bonding between couples), and having kids as an active choice to create a life.
Not long after the pill enabled the sexual revolution, a new technology emerged that allowed gay and infertile couples, as well as single people, to have children: in vitro fertilization. IVF is a simple medical procedure that extracts eggs from women and combines them with sperm from men to create embryos. Couples can then decide which of the embryos to implant.
While IVF was considered controversial at first, as soon as it proved viable in England and the U.S., attitudes quickly changed from skepticism to acceptance. In Japan, for example, about 5 percent of all births now come from IVF. In Denmark, the number is 10 percent, though that is partly because Denmark is a popular destination for women seeking sperm donors and fertility treatments.
Since couples using IVF usually produce several embryos, and sometimes dozens, it is commonplace to use a simple genetic test to determine whether any of those embryos have “aneuploidy.” Aneuploidy occurs when an embryo has too few or too many chromosomes. The most common version of aneuploidy results in Down syndrome, and it is no surprise that couples will generally pick an embryo without chromosomal abnormalities when given the choice.
Polygenic prediction
Over the past two decades, the human genome has been decoded, and genetic testing has become ubiquitous. People get genetic tests to reveal their ancestry, to predict disease susceptibility, or to find out who the biological father of a child is in contested cases.
But a new kind of genetic testing has entered the fertility clinic. Preimplantation Genetic Testing (PGT) can now be done not only for aneuploidy, or for monogenic traits such as Tay-Sachs disease; it can also be done for polygenic traits which involve many genetic variants, each of which has a small effect. Most of the traits we care about—ranging from height and weight, to cancer or schizophrenia—are highly polygenic.
A few companies already offer polygenic risk scores that predict the likelihood that an embryo will develop a specific disease like diabetes. It is inevitable that some will apply these tests in ways that enable couples to select for aesthetic and cognitive traits. The more embryos couples can produce, the greater genetic variability there will be from which couples can choose. Mate choice will constrain the possibilities, but more embryos means more options.
It is important to distinguish embryo selection using polygenic risk scores from gene editing. Selecting one embryo from a set of embryos is as old as IVF. It can be done at random, or it can be guided using polygenic scores. Embryo selection using polygenic scores is very different from gene editing since it involves selecting among whole embryos.
Gene editing is still too dangerous to use on embryos, since it frequently produces off-target mutations that can have harmful effects on a developing fetus. It is possible that at some point in the future, CRISPR, the most common genetic editing techinique, will be used to “spell check” the genome, and maybe even rewrite it in fundamental ways, but we are a long way from that possibility. Few people realize, however, just how powerful embryo selection will become in the near future.
In vitro gametogenesis
IVF will become more potent as our understanding of genetics improves. And IVF will likely become more common as people around the world delay reproduction longer. Having children later raises the chances of infertility, but it also increases the risks to children since older parents pass along more de novo mutations. This means more couples will either need to use IVF to have children, or will use IVF electively in order to minimize disease risks to the children they have.
Polygenic risk scores will become more accurate as the data from genome-wide association studies accumulates. But the game-changer right around the corner is in vitro gametogenesis (IVG). IVG allows scientists to take an adult cell, such as blood or skin cell, and turn it into a pluripotent stem cell (the kind that can become any cell, including a sperm or egg cell).
When IVG becomes a reality for people (it’s already been done for animals), menopause and mutation accumulation will become less important, and couples will be able to create many embryos from which to select without the need for IVF. This means that the genetic variety of a couple’s embryos will be large enough that two short people could select a tall child, or two people at high risk of diabetes or schizophrenia will likely be able to select an embryo at low risk for both.
We will still have sex. And we will still have children. But the link between the two will grow more tenuous. The prospect of artificial wombs is likely to increase this gap even more. An obvious risk is that both sex and babies will be thought of in more instrumental and less romantic terms. An obvious benefit is that our children will have lower risks of disease.
In a series of forthcoming posts I’ll tackle some of the moral questions raised by these new technologies. I also hope to explore how these technologies will alter the way we live.
