Aging as Development: What Biology Teaches Us About Human Agency

Development is not passive; it is a participatory feedback-rich process in which the organism and its environment continually shape one another.

In biology, researchers are fundamentally rethinking how organisms develop. Instead of viewing development as a fixed genetic script—something that simply unfolds on autopilot—they are paying closer attention to how organisms actively respond to their environments,

regulate growth, allocate energy, and participate in shaping the conditions of their own lives.

Development, it turns out, is not passive. It is participatory.

Biologist Isabel Smallegange in a recent study in Academia Biology describes development as a feedback-rich process in which the organism and its environment continually shape one another. She uses the bulb mite to make a case for recognizing agency as important—the capacity of organisms to regulate aspects of their own development.

The bulb mite is a tiny, soil-dwelling creature whose males can develop into two strikingly different physical forms:

• Fighters: Males equipped with large, weaponized legs built to crush rivals.

  
  

• Scramblers: Unarmed males that rely on mobility and speed.

  
  

These forms are not strictly hardwired by DNA. Juvenile growth rate, available food, environmental density, and internal energy allocation determine which pathway emerges. The mite’s own developmental responses directly feed back into the outcome—a phenomenon Smallegange describes as proto-agency. She describes the developmental "trajectories" as a move toward understanding self-directed change.

That shift raises an intriguing question: What if we thought about human aging in much the same way?

We often speak about aging as though development has already concluded. Childhood, adolescence, and early adulthood are treated as periods of growth; aging is what comes afterward. But what if later life isn't just the final stage of a fixed trajectory? What if it remains a period in which we continually respond, adapt, reinterpret, and become?

From Fixed Traits to Lifelong Trajectories

In the biological world, organisms regulate development through physical mechanisms like energy allocation, environmental modification, and context-sensitive responses. A bulb mite isn't consciously choosing its destination. But its growth isn't just an automatic program either. And that distinction holds a powerful lesson for human aging.

Human agency, of course, is far more complex. We don't just respond to our environments; we reflect on our responses. We interpret events, adjust our choices, revise our relationships, and rewrite our internal narratives.

Our lives are defined not only by what happens to us, but by how we integrate experiences into our sense of self.

Unflattening the Older Adult

One phrase from Smallegange’s research stood out for me: traditional demographic models risk "flattening" organisms by reducing them to static traits and average outcomes.

We do something remarkably similar to older adults. We flatten people into age brackets, diagnoses, deficits, and care needs. We put them into passive categories: senior, frail, dependent, retired. In doing so, we lose sight of the active, developmental person who is still there—reading, responding, choosing, adapting, and creating meaning.

To "unflatten" an older adult means seeing them not as the static summary of everything that came before, but as someone actively engaged in the construction of life. This shift is more than conceptual—it is deeply ethical. It changes what society expects from later life, and more importantly, what older adults expect from themselves.

Still Becoming

A tiny soil mite cannot tell us what it means to grow old. But the developmental biology surrounding it offers a brilliant reminder: trajectories are shaped through continuous interaction.

Aging certainly brings changes we do not choose. Our bodies, health, relationships, and circumstances shift. Agency does not mean having complete control over everything that happens to us. It means recognizing that what happens is never the end of the story.

Perhaps the most important shift we can make is to stop viewing later life as a fixed destination or a decline curve. We are not passive recipients of time. We are active participants in what comes next.

We are still becoming.

Source: Smallegange, I. M. (2026). From traits to trajectories: Development, agency and a phenotypic gap in demography. Academia Biology,