The future of human evolution may be determined not just by scientific capability, but by the metaphors we use to describe it.
Imagine a future where parents can select characteristics for their children like items from a catalog—high intelligence, musical talent, athletic prowess, and immunity to disease. This vision of human genetic modification relies on a hidden assumption: that human traits function as independent, interchangeable building blocks. This concept, which scholars call "modular ontology," shapes both the possibilities and the perils we envision for genetic engineering. As we stand on the brink of potentially redesigning human biology, understanding this conceptual framework becomes crucial for making ethical decisions that will affect generations to come.
In the debate over human germline genetic modification (HGGM), participants often imagine future people abstractly, defined by conventional characteristics familiar from science fiction: intelligence, disease resistance, height, and various physical attributes1 . To discuss these concepts precisely without the biological baggage of terms like "phenotype" and "trait," researchers have proposed the term "persemes"—the units of difference for hypothetical people1 5 .
Similar to how "mythemes" describe units of narrative structure, persemes are the culturally salient units we use to assign differences to imagined people1 . In the HGGM debate, these persemes are frequently conceptualized as modular entities—similar to building blocks that scientists could theoretically select and assemble into a future person1 .
This modular framework treats persemes as if they possess three key properties:
Each perseme can be chosen individually without affecting other persemes
They exist as components within future people rather than being imposed through social context
They function as similar types of entities that can be combined without fundamental conflict
This way of conceptualizing human traits has deep historical roots and significant ethical implications that often go unexamined in public discourse about genetic engineering.
The conceptual origins of treating human characteristics as modular building blocks trace back to the early days of genetics and the eugenics movement1 .
With the emergence of classical genetics, eugenicists like Charles Davenport assumed that individual genes caused a wide variety of human traits1 . Davenport's "Trait Book"—developed to help volunteers gather information about physiological, mental, and social characteristics—flattened and equalized all human characters, from beauty to Huntington's disease to altruism1 .
American eugenicists imagined genes acting in a modular fashion, with 1-to-1 correspondences between independent genes and phenotypes—an approach sometimes called "beanbag genetics"1 . As one bioethicist explained this mindset: "You add or pull out a bean and get the effect you seek"1 .
Though this simplified model of heredity was largely abandoned by scientists by the 1920s, it resurfaced in the 1980s and 1990s as scientists attempted to identify candidate "genes for" various phenotypes1 . When bioethicists joined these discussions, they generally admitted that the enhancements that most interested them had no specific identified molecular basis, yet they continued discussing them as discrete, selectable units1 .
The persistence of modular thinking in genetics discussions has strong psychological foundations. Human cognition naturally tends to categorize and compartmentalize complex phenomena—it helps us manage information about the world1 . When imagining future people and their characteristics, this tendency manifests in how we conceptualize genetic modification.
Modular ontologies for genetically modified people create a sense of psychological distance that allows ethicists and scientists to discuss potentially troubling implications without confronting the full complexity of what it means to be human1 .
The modular ontology of persemes significantly influences bioethical approaches to human genetic modification, often in ways that escape critical examination.
The modular framework reinforces the idea of human capacities as natural primary goods subject to distributive justice1 . When traits are conceptualized as independent modules, they become commodities that can be justly or unjustly distributed across populations—raising questions about whether society has an obligation to provide "better" traits or whether such distribution would create unprecedented forms of inequality.
Modular thinking about genetic traits supports the use of objective list theories of well-being1 . These theories suggest that certain goods contribute to human flourishing regardless of individual preferences. When persemes are treated as discrete units, they easily slot into such lists as objective components of a good life, potentially overlooking how the value of traits depends on personal, social, and environmental contexts.
Perhaps most importantly, assumptions of modularity may limit the ability of stakeholders with alternative perspectives to participate meaningfully in the HGGM debate1 . By framing the discussion in terms of selecting independent modules, the conversation automatically excludes viewpoints that emphasize the relational, contextual, and emergent aspects of human traits and identity.
While the modular ontology persists in ethical discussions, actual advances in genetic engineering reveal a far more complex reality.
Recent developments in CRISPR technology demonstrate both the potential and the limitations of treating genes as modular components. The first personalized in vivo CRISPR treatment was administered in 2025 to an infant with CPS1 deficiency2 . Developed and delivered in just six months, this bespoke therapy required a multi-institutional collaboration and was delivered via lipid nanoparticles (LNPs), with doctors able to administer multiple doses to increase editing efficiency2 .
This case serves as both a proof of concept and a cautionary tale—while we can increasingly intervene in specific genetic sequences, the process remains complex, context-dependent, and requires ongoing adjustment rather than simple "module insertion."
| Delivery Mechanism | Description | Applications | Limitations |
|---|---|---|---|
| Lipid Nanoparticles (LNPs) | Tiny fat particles that form droplets around CRISPR molecules | Liver-focused diseases (hATTR, HAE, high cholesterol) | Natural affinity for liver limits other applications |
| Viral Vectors | Modified viruses used to deliver genetic material | Previous gene therapies (SCID, LCA) | Immune reactions prevent redosing |
| Cell-Specific LNPs | LNPs engineered to target specific organs | Experimental stage, not yet in trials | Potential for more precise targeting |
The reality of how genetic interventions work reveals the oversimplification of the modular approach. For instance, Intellia Therapeutics' phase I trial for hereditary transthyretin amyloidosis (hATTR) used CRISPR-Cas9 delivered by LNPs to reduce the production of a disease-related protein in the liver2 . The treatment showed quick, deep, and long-lasting reduction in TTR protein levels—but rather than "fixing" a simple modular component, it worked by breaking a gene to stop it from making a protein that drives a disease process2 .
If the modular ontology of persemes is both psychologically compelling and scientifically inadequate, how might we develop more sophisticated ways of thinking about genetic modification?
A more accurate approach would recognize that traits are rarely independent—they interact in complex ways both biologically and socially. Thinking in terms of interconnected networks rather than isolated modules would provide a more realistic foundation for ethical deliberation.
The modular approach tends to overlook the importance of subjective experience and personal meaning in how traits contribute to well-being. The same characteristic may have vastly different implications depending on an individual's goals, values, and social context.
Many traits considered for genetic modification are strongly influenced by social context and interpretation. Rather than being internal components of a person, their significance emerges through relationships and social structures that the modular framework tends to render invisible.
As genetic technologies advance—from the Synthetic Human Genome Project that aims to build human DNA from scratch6 to increasingly sophisticated CRISPR therapies2 —the need for thoughtful ethical frameworks becomes more urgent. The concept of modular ontologies and persemes reveals how our unexamined assumptions shape what we imagine to be possible and desirable.
Moving beyond the modular perspective doesn't mean abandoning the potential benefits of genetic technology. Rather, it means developing a more sophisticated understanding that acknowledges complexity, context, and connection. It means recognizing that we are not designing machines from interchangeable parts, but intervening in complex biological systems with emergent properties and profound connections to personal identity and social meaning.
The challenge is not just to decide which building blocks to combine, but to cultivate a deeper understanding of what makes a life meaningful and what kind of society we want to create—questions that no modular ontology can adequately capture. As we continue to develop the power to reshape human biology, we must similarly evolve our conceptual tools to match the complexity of the decisions we face.
For further reading on this topic, see "Modular Ontologies for Genetically Modified People and their Bioethical Implications" in NanoEthics (2024), which introduces the concept of persemes and explores the philosophical ramifications of modular thinking in genetic ethics.