The Hidden Economics of Borrowed Functions

Jun 09, 2026

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What do a pregnancy protein and an airline route have in common?

At first glance, almost nothing. One belongs to the deep machinery of mammalian reproduction, the other to the spreadsheet logic of aviation revenue. Yet both point to the same unsettling truth: the most successful systems often do not invent their core functions from scratch. They borrow, repurpose, and then lock in what works.

That is a provocative idea because we are taught to admire purity in design. We imagine biology as a clean blueprint and business as a carefully optimized machine. But the deeper pattern is messier and more interesting: evolution and markets both reward whatever can be captured, stabilized, and scaled, even if its origin is accidental or opportunistic. A retroviral protein becomes part of the placenta. A domestic flight route becomes a billion dollar cash machine. In both cases, the winner is not the most elegant starting point, but the one that turns an ordinary connection into an indispensable one.

The real question is not whether a system can create value. It is whether it can turn dependency into advantage.

The strange power of captured utility

In mammalian evolution, placentation is one of the most important innovations ever seen. It lets a mother and embryo coordinate resource exchange, protection, and development in a way that transforms reproduction itself. What is striking is that this capability did not arise entirely from a neatly designed mammalian toolkit. Part of it came from a captured retroviral envelope protein, a once foreign element that became integrated into the biology of the host.

That sounds almost like theft, but biology is rarely sentimental about origins. If a piece of genetic material can be domesticated into a useful role, evolution keeps it. The source of the tool matters less than the function it can reliably perform. A viral envelope protein, originally built to help one entity enter another, can be repurposed to fuse cells in the placenta. What was once invasive becomes relational.

The aviation example carries the same logic in a different register. Consider a domestic route such as Sydney to Melbourne, which earns enormous revenue despite a decline in passenger numbers. The key is not simply volume, but position in the network. This route is not valuable because it is glamorous. It is valuable because it sits at a choke point where demand, airline competition, and pricing power concentrate. The route has been turned into a dependable, recurring transfer of value.

This is the common structure: a function first appears in one context, then gets incorporated into a larger system where it becomes indispensable. The placenta captures a molecular trick. Airlines capture a travel corridor. In both cases, the system becomes stronger not by starting over, but by absorbing an external advantage and making it foundational.

The most durable advantages are often not invented. They are domesticated.

Why the best systems are built around bottlenecks

There is a temptation to think that success comes from abundance: more genes, more routes, more passengers, more features. But both biology and economics suggest the opposite. Stability often emerges from managing bottlenecks.

A placenta is, in a sense, a bottleneck made productive. It is the controlled interface between mother and fetus, a place where exchange is tightly regulated. Too much permeability is dangerous. Too little exchange is fatal. The point is not open flow, but selective flow. Evolution discovered that survival depends on building an interface that can both connect and filter.

Top flight routes work the same way. A route like Sydney to Melbourne is not merely a line on a map. It is a concentrated exchange corridor where travelers, schedules, and airline capacity collide. The route becomes economically powerful because it channels demand through a limited number of seats and carriers. Scarcity, not abundance, creates the margin.

This is a useful mental model: valuable systems are often selective membranes, not open pipes.

Think about a luxury restaurant that seats only a few dozen people but charges premium prices. Think about a university admissions office with more applicants than places. Think about a software platform with an API that becomes the only practical gateway to a market. In each case, the system earns power by being the point through which exchange must pass.

That is why the link between a placental protein and airline revenue is not a joke. Both show that the highest leverage often comes from controlling the interface, not the raw material.

From invasion to infrastructure

The most interesting part of the biological story is not just capture, but conversion. A retroviral element is not merely tolerated. It is transformed into infrastructure. The foreign becomes familiar, then essential. That transformation is one of evolution’s greatest talents, and it has a striking parallel in business.

A flight route begins as a connection between two cities. Over time, if enough schedules, habits, business ties, and pricing conventions form around it, the route stops being just a path and becomes an infrastructure layer for regional life. People do not fly it only when they feel like traveling. They use it because meetings, supply chains, and family patterns have adapted to its existence. The route ceases to be optional. It becomes part of the background architecture of the economy.

This is why market leaders often defend not products, but habits. A product can be replaced. A habit is embedded in calendars, routines, and institutions. Once a route is structurally embedded in the lives of businesses and consumers, it acquires the same kind of stickiness that a biological feature has when it becomes wired into development.

Here is the deeper lesson: the decisive move is not acquisition alone, but domestication over time.

A company can buy a competitor, but that does not mean it has captured the loyalty, timing, or workflow the competitor once enabled. Likewise, evolution can encounter countless foreign elements, but only some become integrated into a developmental program. The test is not novelty. The test is whether the system can make the borrowed function reliable enough to build around.

The thesis: advantage is often a story of dependency

We usually speak about strength as independence. Strong organisms are self-sufficient. Strong companies are vertically integrated. Strong routes are high volume. But these examples suggest a more paradoxical idea: strength often comes from creating the right kind of dependence.

The placenta makes the embryo dependent on a carefully regulated exchange with the mother. But that dependence is exactly what enables growth. The airline route makes travelers dependent on a particular corridor and timetable. But that dependence is what lets airlines extract value from concentrated demand. In both cases, the system is powerful because it creates a stable dependency that is difficult to bypass.

That may sound cynical, yet it is not inherently exploitative. Dependency can be regenerative when it supports life, coordination, and reliability. A good public transit hub creates dependence too, but in a way that reduces total friction. A good university or hospital becomes a dependency in the lives of families, but often because it reliably solves problems others cannot.

The important distinction is this: healthy dependency is not fragility, it is structured interdependence. The placenta is fragile in one sense, but it is also exquisitely designed to manage risk. A high revenue route is vulnerable to shocks, yet it is also protected by strong habits and limited substitutes. Power emerges where exchange becomes both necessary and governed.

So the deeper question is not whether a system can avoid reliance on outside elements. It cannot. The question is whether it can convert reliance into architecture.

A practical framework: the capture, filter, and lock model

If these examples feel abstract, use this simple framework to analyze any durable system.

1. Capture

Some external element enters the system: a gene, a technology, a customer corridor, a partnership, a habit.

The key question is not where it came from, but whether it solves a real problem. Retroviral material solved a developmental problem. A busy route solves a connectivity problem. Good systems are unusually open to useful strangers.

2. Filter

The system does not accept everything. It screens, adapts, and repurposes.

In biology, only certain captured elements can be made compatible with development. In markets, only certain routes become profitable enough to justify sustained investment. Filtering is what turns chaos into function.

3. Lock

The best systems make the new function hard to remove.

The placenta is not a temporary hack. It becomes part of the reproductive program. A top route becomes defended by schedules, pricing, alliances, and customer expectation. Once a function is locked in, it no longer feels like an add on. It feels natural.

The strongest systems are not those that resist change. They are those that convert change into structure.

This framework matters because it applies far beyond biology or aviation. A startup that adopts a niche user behavior and turns it into a product standard. A city that converts an old rail corridor into a transit spine. A media platform that transforms a one time novelty into a recurring ritual. All are acting out the same pattern: capture, filter, lock.

What this means for how we build

The temptation in design is to ask, “What should we invent?” The more interesting question is, “What useful thing already exists at the edge of the system, and how can we make it foundational?”

That change in perspective alters how we think about strategy.

Instead of pursuing originality for its own sake, look for foundational borrowing.

Instead of maximizing openness, design for productive selectivity.

Instead of chasing scale too early, identify the interfaces where exchange concentrates.

Instead of assuming dependency is weakness, ask whether the dependency can be made reciprocal, reliable, and hard to replace.

This is especially valuable in organizations. Many teams fail not because they lack talent, but because they never turn useful one off tactics into stable infrastructure. They keep improvising every week instead of asking which improvisation should become standard operating procedure. They discover a good workflow, a good customer segment, or a good internal tool, but never lock it into the organizational body.

Biology does not make that mistake. It remembers what works by embedding it. Markets do the same when they are disciplined. The best route is not just busy. It becomes expected.

Key Takeaways

Look for borrowed advantages. The most powerful functions often come from outside the system and are later domesticated.
Treat bottlenecks as opportunities. Value frequently concentrates at controlled interfaces, not in open expansion.
Aim to convert habits into infrastructure. A repeated behavior is far more durable when the system is designed around it.
Think in terms of capture, filter, lock. Useful systems absorb, refine, and stabilize external inputs until they become essential.
Redefine strength as structured interdependence. Durable systems do not eliminate dependency. They arrange it so that exchange becomes reliable and productive.

Conclusion: the future belongs to the domesticated

The deepest connection between a retroviral protein in a placenta and a lucrative flight corridor is not that both are unusual. It is that both show how value emerges when a system turns a contingent connection into an organizing principle.

We often celebrate invention as if the future belongs to pure originality. But much of what lasts is assembled from borrowed pieces, then stabilized until it feels inevitable. A placenta is a compromise that became essential. A flight route is a corridor that became infrastructure. In both cases, the world is being shaped by systems that know how to take the accidental and make it necessary.

That may be the most useful reframe of all: the best systems do not merely grow. They learn how to domesticate what crosses their borders.

And once you see that pattern, you start noticing it everywhere, in genomes, in cities, in companies, in habits. The winners are not always the purest creators. Often, they are the best translators of outside power into inside structure.