The Misread "Why": 3 Biology’s “Because” — Natural Selection as Internal Necessity

One of the reasons the word why causes so much conceptual trouble is that it migrates easily across domains while quietly changing its function. What counts as an excellent answer to why in one domain becomes a category error in another.

Biology is a particularly instructive case. Here, why often appears to do real explanatory work — and, crucially, it does so without appealing to metaphysical purpose. This has led many readers, both sympathetic and hostile, to think that biology has somehow smuggled teleology back into science under a different name.

It hasn’t. But it has done something subtler, and more interesting.

The Appearance of Purpose

Consider the familiar form of biological explanation:

Birds have hollow bones because lighter skeletons aid flight.

To an unwary ear, this sounds goal-directed. The bones are hollow in order to make flight possible. Evolution, on this reading, looks like an engineer with foresight, selecting traits because of what they will later achieve.

Biologists are quick to deny this interpretation — rightly so. Natural selection does not anticipate outcomes. It does not plan. It does not aim.

But what, then, licenses the because?

Selection Is Not a Cause in the Ordinary Sense

Natural selection is often spoken of as a causal force, but this is already a metaphor — and a potentially misleading one. Selection does not push, pull, or produce traits the way a force produces motion or a chemical reaction produces a compound.

Instead, selection names a constraint structure:

• given variation

• given heredity

• given differential survival and reproduction

certain trait distributions are internally necessary over time.

This is not causation layered on top of biology. It is biology articulating its own internal logic.

When we say that a trait exists because it confers a reproductive advantage, we are not identifying an efficient cause that brought the trait into being. We are identifying the conditions under which that trait is retained and stabilised within a population.

The because here is explanatory, not generative.

Internal Necessity, Not External Purpose

This is the same kind of necessity we saw in gauge symmetry, now playing out in a living system.

In physics, certain quantities must be conserved given the symmetry constraints of the theory.

In biology, certain traits must proliferate given the constraints of variation, heredity, and selection.

In neither case is there an external reason why the system itself exists or is the way it is. The explanations remain internal to the theoretical framework.

The mistake arises when this internal necessity is misread as an answer to a deeper ontological why:

Why do organisms exist at all?

Why does life have this structure rather than another?

Natural selection does not answer these questions — and it does not pretend to. It answers a different one:

Given life of this kind, why do we observe these forms rather than others?

That is a perfectly legitimate because. It just isn’t the one people often think they’re hearing.

Why Biology Feels More Dangerous Than Physics

Biological explanations feel more philosophically loaded than physical ones because they track functional difference. Traits matter. They make a difference to survival and reproduction.

This difference easily slides into value-laden language:

• better adapted

• more efficient

• successful strategies

But these are descriptions of system-relative success, not global purpose. The values are endogenous to the system, not imposed from outside it.

Confusing the two leads to familiar errors:

• treating evolution as progressive

• reading moral lessons into biology

• assuming that explanatory success implies ontological completeness

Once again, the problem is not biology. It is the misread why.

Biology’s Proper Achievement

Biology shows us that because can be powerful without being metaphysical.

It can:

• explain stability without intention

• account for form without foresight

• generate necessity without purpose

In doing so, it offers a model for how far explanation can go — and where it must stop.

The temptation to push further, to ask biology to tell us why there is life at all, is understandable. But it is a different question, requiring different tools.

In the next post, we will turn to a domain where the misread why becomes even more treacherous: social systems — where explanation, justification, and legitimacy are far harder to keep apart.

The Misread "Why": 2 Constraints vs Causes — Lessons from Gauge Symmetry

In the previous post, we saw how “because Y” can be misread as an ontological explanation when it is really a theory-internal statement. Physics offers a particularly vivid illustration of this misread: gauge symmetry and the existence of light.

This post explores how constraints in physics operate as enabling conditions, not causal agents, and what lessons we can draw for responsible explanation.

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Gauge Symmetry and Physical Necessity

Gauge symmetry is a central principle in modern physics. It specifies how certain fields may vary while preserving internal consistency. Within this framework, the existence of photons — the quanta of light — follows necessarily. In other words, light is unavoidable given the constraints imposed by gauge symmetry and the structure of electric charge.

Notice the level of explanation: it is entirely internal to the theory. It says nothing about why the universe has gauge symmetry or why charges exist. It tells us only that once these structural features are adopted, certain phenomena must appear.

This is a textbook case of theory-internal necessity.

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Constraints Enable, They Do Not Cause

It is tempting to translate this into causal language:

• “Gauge symmetry produces photons.”

• “Charges cause light to exist.”

Yet this is a category mistake. Constraints in physics are not agents. They do not act. They enable intelligible patterns within a theoretical framework. They specify the space of possibilities rather than pushing the world in one direction.

A more accurate framing is:

Given the structure of possibility defined by gauge symmetry, the behavior we observe is required.

This subtle distinction preserves the explanatory power of physics without stepping into unwarranted ontological claims.

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Why This Distinction Matters

Physicists often slide into the misread “why” effortlessly. It is easy to hear an internal dependency as a metaphysical declaration:

• The necessity within the theory feels deep.

• It appears to answer the ultimate question: “Why is there light?”

Yet the answer is conditional. It is true only relative to the adopted constraints. Mistaking it for ontological necessity obscures the real boundaries of explanation and risks the allure of metaphysical overreach.

Recognizing the distinction allows us to:

• Appreciate the success of theoretical physics.

• Keep track of the level at which explanations operate.

• Maintain lucidity about what has actually been answered.

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General Lesson

Gauge symmetry is a perfect illustration of a general principle: constraints explain intelligibility, not existence.

• In physics, constraints specify which phenomena are possible or necessary within a theoretical framework.

• In other domains — biology, society, symbolic systems — the same pattern emerges: constraints shape what can occur, without themselves being ultimate causes.

The discipline is to notice when a dependency claim is being heard as a metaphysical explanation, and to own the cut being made.

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Looking Ahead

In the next post, we will see this pattern in biology. Natural selection provides another instance where theory-internal necessity is often mistaken for ontological causation. Just as gauge symmetry explains the inevitability of photons within a framework, so evolutionary principles explain the distribution of traits within a population and its environment.

By tracing the pattern across domains, we can cultivate clarity and responsibility in how we hear and make explanations.