The Longtermist Case Against Genetic Selection

Biomedical Ethics, Dec 8 2025

Introduction

In 2018, the Chinese scientist He Jiankui was the first person to successfully create genetically edited babies. Using CRISPR-Cas9 technology, he introduced a mutation into a gene called CCR5 which provides resistance to HIV infection. While he initially was praised for advancing scientific knowledge, he was soon sentenced to several years in prison for his actions. This sudden shift in public and governmental opinion has sparked a conversation on the ethics of genetic modification. Many people support the use of gene-editing to cure potentially fatal genetic conditions such as sickle cell anemia, but some question the consequences of editing genes to make improvements from a person’s baseline, also known as genetic enhancement. From changing eye color to improving physical fitness, gene-editing technology could provide parents the ability to create ‘designer babies’ with traits that they consider ideal. 

In this paper I will argue that enhancing people through germline genetic editing or genetic selection should remain legally prohibited for the foreseeable future because of its long term risks to the human population. In order to strengthen my argument I will not rely on the social implications of gene-editing, including eugenics and increasing social inequality, despite their significance in regards to this issue. Instead, by drawing on longtermism, I will focus on the effects of genetic modification on the population and survival of the human species. Genetic enhancement poses risks that outweigh the benefits because it threatens genetic diversity, which is essential for resilience of a population in the face of potential pandemics or other environmental disasters. 

Ethical Risk of Medical Treatment

Two of the main principles guiding biomedical ethics are beneficence (obligation to do good) and non-malficence (obligation to avoid doing harm.) These principles often come into conflict with each other in a medical setting because treating any condition usually accompanies some risk of harm. Medical treatments are justified when the expected benefits outweigh the risks. In their book Know Your Chances: Understanding Health Statistics, Woolshin and Schwartz emphasize that “benefit is only half of the story.” When considering genetic enhancement, the potential benefit is hard to ignore. However, the long-term consequences of technology like CRISPR is unknown. There is a potential risk for causing harm to both the individual and the population overall, which violates the principle of non-maleficence. 

Advocates for genetic enhancement such as Julian Savulescu and Guy Kahane argue for the principle of procreative beneficence. According to this principle, parents have a moral obligation to select a child who will have the best expected life. They argue that selecting children with desirable traits – such as greater strength or intelligence – will improve the child’s life and is therefore a parent’s duty. Their argument focuses on one of the principles: beneficence, without thoroughly considering the risk of harm. The principle of procreative beneficence, while useful, is insufficient for evaluating treatment that has irreversible, generational consequences. 

There is an important distinction between somatic gene editing, and the germline editing or genetic selection that Savulescu and Kahane argue for. Postnatal genetic enhancement targets somatic cells. It does not change the germline cells (sperm and egg) and therefore cannot be inherited. Prenatal genetic selection or enhancement does not just affect the individual. Editing the genome of an embryo or selecting an embryo based on genetic screening involves changes to the germline. Any traits that are selected for will be inherited by future generations. While modifications to maximize the wellbeing of a single child may seem desirable, it raises serious risks to the whole population. The question is not simply whether a trait is beneficial today, but whether altering our genetic baseline is a threat to the survival of our species in the face of a changing climate and novel viruses. 

An Argument for Preserving Genetic Diversity

Humans already have relatively low genetic diversity compared to the other primates most similar to us. Our genomes are upwards of 99.9% identical and we have a lower median genetic diversity than all but 15 of 233 primates studied (Kuderna et. al.) Genetic selection for ‘optimal’ traits would further homogenize the population and decrease genetic diversity. Selecting traits that are most beneficial now eliminates traits that could not only be beneficial in the future, but essential to the survival of our species. Therefore, it is reasonable to argue that the vulnerability to our population introduced by genetic selection outweighs the individual benefits. 

Other species that show even less genetic diversity than ourselves are susceptible to extinction from environmental or biological threats. For example, the Channel Island fox has very low genetic diversity because of their isolated location. This species has been close to extinction on multiple occasions due to outbreaks of disease and a changing climate. A single outbreak of canine distemper in 1998 killed approximately 90% of the entire population on one island. In the wake of the COVID-19 pandemic that killed millions, it is reasonable to consider the risk of extinction due to decreased genetic diversity. 

As a positive example of genetic diversity, consider the story of the peppered moth . This moth species originally had a light-colored wing pattern because it helped them blend in with the lichen on trees. However, the English industrial revolution polluted the atmosphere and killed most of the lichen. When this happened, the light colored moths died because they were easily seen by predators and moths with a darker coloration thrived. If the dark-colored wing trait had been completely eliminated, the peppered moth could have faced extinction. Traits that are not desirable at one moment in time can quickly become evolutionarily desirable due to environmental changes that we can’t predict. 

Long-term Effects of Inheritable Change

Despite how much we now know, our understanding of the genome is still in its infancy. The human genome was not fully sequenced until 2003 – less than 25 years ago. Given the opportunity to select a child’s traits, parents will not make their decisions with genetic variation in mind. The determination of desirable traits may be shaped by class or dominant cultural values, leading to erasure of minority genetic traits. Cultural forces will drive a convergence towards a list of optimal traits. 

Additionally, we may eliminate traits that we do not yet understand. There are complex relationships between genes, and most traits are polygenic, meaning they are determined by the combined effect of more than one gene. Evolutionarily undesirable traits are already selected against at the population level through natural selection. It is reasonable to assume that some traits persist because they provide a benefit in certain conditions. 

Cystic fibrosis is a well-known example of such a trait. Having two copies of a mutated CFTR gene causes cystic fibrosis, which is a condition that causes illness and even death. Having one copy of a mutated CFTR gene provides protection against Mycobacterium tuberculosis, the bacteria that causes tuberculosis (Bosch et al.) In areas where tuberculosis is endemic, this trait persists because it is beneficial for survival. Not only could we underestimate the significance of certain genes for protection against diseases that already exist, we are completely unable to predict the importance of genes in the cases of novel viruses that do not exist yet. Homogenizing the population could leave us vulnerable to extinction. 

From a longtermist perspective, this outcome is ethically troubling. Longtermism, as described by William MacAskill, is the argument that future people matter just as much as people who are alive now. Since they will exist in the future, we must consider their interests. If our species survives as long as the average mammalian species, there will be billions or even trillions of future people. Decisions we make, such as editing the human genome, must be made in consideration of those future people. Germline editing could limit their survival. Therefore, it is not morally permissible to consider our own interests, like having enhanced intelligence or strength, over the lives of people who will exist in the future. 

Addressing Objections

One may argue that the idea of genetic homogenization overlooks the complexity of human culture. For example, some societies may value traits like height, while others find them undesirable. Cultural norms surrounding intelligence, athleticism or skin tone vary widely throughout the world. If genetic enhancement or selection became the norm, it is plausible that parents from different cultures may select different traits. 

The concept of genetic drift complicates this objection. Genetic drift refers to the random loss of alleles in a population over time, regardless of whether those alleles are beneficial. When a population is sufficiently large, genetic drift eliminates alleles slower and the population stays at equilibrium. In smaller populations, there is increased genetic drift because the gene pool is smaller and random events have a greater impact. If one considers each culture a separate population due to their different selection preferences, each will experience accelerated loss of diversity within the population due to their smaller population sizes. Even if different cultures initially value different traits, each group’s genome will become homogenized, effectively reducing diversity within groups. Perhaps in this case one culture loses an allele that protects them against a novel virus. Although other cultures may survive and avoid extinction, loss of an entire culture is also not desirable. 

Furthermore, while cultures might choose different traits today, preferences shift over time. Realistically, in our globalized world each culture is not a distinct entity, and values often converge. Some traits, like intelligence, or resistance to disease, are nearly universally desirable. Even if cultural variation provides some initial protection against homogenization, it is unlikely to create a long-term safeguard against it. 

Conclusion

While genetic enhancement is an attractive solution to improving individual lives, this paper has argued that it should remain legally prohibited in the foreseeable future because of its long-term impact. Unlike somatic gene editing, germline editing and genetic selection introduce heritable changes that affect future generations. By applying the view of longtermism, I highlighted that future people matter just as much as those who are alive today. Our climate is constantly changing, and viruses are evolving. We should not prioritize our current interests over the survival of future generations facing these issues. Preserving genetic diversity is not just a biological concern, but also a moral one.

Bibliography

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