The Crabs Keep Winning

Biologists have documented several cases where evolution turned completely unrelated creatures into crabs. No one can explain it. Some now suspect the coastline is sentient and simply keeps ordering the same thing off the menu. Interface design behaves similarly, although our coastline is user research.

There is a curious pattern in nature where entirely unrelated creatures keep evolving into something suspiciously crab-shaped. Biologists call it carcinisation. It is one of evolution’s recurring jokes, the sort of joke that becomes funnier the longer you stare at it. Centuries of drift, mutation and opportunity, and somehow a surprising number of the winners walk sideways and have ideas about pincers.

When you step back and look at the last couple of decades of interface design, you can see a similar drift. Different teams. Different industries. Different stacks, business models and internal arguments. Yet we keep edging towards the same shapes. Navigation collapses into hamburgers. Buttons become rounded rectangles. Cards become the universal solution. Notifications arrange themselves politely in the same few corners like shy hermit crabs. It is not that designers lack imagination. It is that the environment is strongly opinionated about what works.

You keep sanding and shaping. You keep pruning and adjusting. You shave off the awkward bits and reinforce the useful ones. And then one day you wake up and realise you have accidentally made a crab.

This is an article about why that happens, and why it is not a tragedy. It is simply the world doing what the world does.

When Everything Wants To Be A Crab

Convergence appears everywhere in nature. Dolphins and ichthyosaurs and sharks all end up with the same efficient teardrop shape. Birds and bats solve flight with variations on the wing. And then there are the crabs: the great quiet success story of the shoreline. Independent lineages, all solving the same environmental puzzle in the same way.

Digital ecosystems have their own environments. Their own pressures. Their own survival tests. And the same strange phenomenon keeps showing up there too. Unrelated teams continually rediscover the same patterns, the same positions for controls, the same flows, the same comforting geometry.

If you stick that strange shell to you ear, you can almost hear the tide going in and out.

Why Good Solutions Converge

Evolution does not converge because organisms copy each other. It converges because the environment sorts ideas through a sieve. Shorelines have opinions about body shapes. Forests have opinions about limbs. The deep ocean has opinions about eyes.

Interfaces have their own opinions. They reward:

• Predictability.
• Consistency.
• Low cognitive load.
• Ease of scanning.
• The absence of small irritations.

People move through digital spaces like they drive cars – with muscle memory, not conscious thought.

That creates a behavioural environment with very strong currents. If two teams start from different places but aim for ease and clarity, they will often arrive at something uncannily similar. It is not copying. It is parallel evolution.

And no matter how many times we reinvent search bars, they migrate upwards. They always migrate upwards.

The Sandbox Effect

Designers do some of their best work when there are boundaries. Too few constraints and everything gets squishy. Too many and everything ossifies. Somewhere in the middle you find the sweet spot where creativity does not flail about but instead sharpens itself.

Carcinisation is this in biological form. The shoreline is a tough room. Waves, predators, shifting terrain. If you are going to survive there, your shape needs a certain set of properties. A shell that takes a beating. Limbs that stabilise. A posture that can cope with currents. A crab is not inevitable because nature loves crabs. It is inevitable because the shoreline does.

Software environments are every bit as opinionated as shorelines. They quietly reward:

• Navigation you do not have to hunt for,
• touch targets that do not require the fine motor control of a rocket surgeon,
• type that does not make a user squint,
• and gestures that feel like they belong.

So we design variations of a tab bar for a decade and, after all the drifting about, we arrive once again at a tab bar. A slightly better one, but still recognisably a cousin of every other tab bar. The environment has spoken.

Iteration Is Evolution’s Cousin

Biology runs on mutation and selection. Design runs on iteration and feedback. The scale is different but the rhythm is the same.

You ship something slightly odd. People use it in ways you did not predict. You watch the recordings. You sigh. You correct. You sand another corner. You simplify one bit, emphasise another, remove the frankly weird bit you persuaded yourself was charming.

Software rarely grows. It accumulates outcomes.

A good interface is less a moment of inspiration and more a sedimentary record of decisions. You can almost feel the layers when you touch it. The small corrections. The careful shaping. The moments when confusion appeared in the data and you nudged the design so the next user would not trip over the same stone.

And as all those nudges accumulate, the thing begins to resemble the shapes that have already proven themselves.

The crab returns.

The Myth of Radical Originality

There is a persistent idea that great design must be radically original. And yes, originality has its place. It can be a powerful storytelling device. It can reinforce a brand. It can give a product personality.

But radical novelty in interfaces is a bit like evolving an octagonal cow. The environment will not reward you for it.

Interfaces live inside ecosystems that thrive on familiarity. Users carry interaction memories from app to app. They know what a button looks like before they see it. They know what to expect from a modal. Breaking those deep-rooted expectations is rarely liberating. It is usually irritating.

Designers want to create birds. The market quietly asks for crabs.

The most interesting innovation usually happens in micro-adjustments. A refinement to a gesture. A small shift in pacing. A clever detail in a scrolling behaviour. Newness at the level of texture, not tectonics.

When Divergence Is Necessary

But let us not get carried away. Convergence is not the whole story. Nature values variation. So does good design.

Some problems demand fresh shapes:

• A new interaction paradigm.
• A leap forward in accessibility.
• A shift in device capability.
• Or the discovery that an old pattern no longer solves a modern need.

The trick is knowing when you are breaking a pattern because the environment has changed, rather than because you woke up with an itch for novelty.

If everything becomes crab-shaped, the shoreline becomes fragile. You need other shapes in the mix. Other approaches. Other perspectives. That is how ecosystems stay healthy.

And the same goes for design systems. A pattern is a guide, not a decree.

The Slow Drift Towards Crabness

Look at the history of interface design and you can see this drift happening in real time.

Navigation menus:

from sprawling lists to tidy sidebars to collapsible panels to the same four or five recurring arrangements.

Buttons:

from fizzy bevelled bricks to austere flat squares to soft rounded lozenges that seem to settle at a universal comfort radius.

Cards:

crawling into almost every layout because the format is flexible, scannable, and gives information room to breathe.

Notifications:

all clustering in the same few corners because that is where the eye expects trouble.

And search bars, always rising to the top like cream.

The longer a product survives, the more it resembles its neighbours. Not because anyone copied anyone. Because a shared environment sculpts them the same way a shoreline sculpts the creatures that live on it.

Complexity, Managed Not Flattened

So here is where I bring this into my ongoing work on complexity.

Carcinisation is not about tidiness. Crabs are incredibly complex creatures. They are simply complex in the right places.

A good interface behaves the same way. It arranges complexity so that users do not experience it all at once. It gives them a calm surface and strong invisible machinery underneath. The visible part gets simpler. The backstage part gets smarter. And this is not a contradiction. It is a strategy.

Iteration slowly moves complexity away from the surface. Carcinisation does something similar. It leans into the shape that keeps the organism safe while letting the internal workings become richer and more capable over time.

The result is form that looks deceptively simple from the outside yet handles an extraordinary amount of mess under the shell.

Where The Metaphor Breaks (In A Good Way)

Every metaphor breaks somewhere and this one breaks delightfully.

Evolution has no deadlines.

Evolution has no stakeholders.

Crabs do not hold workshops.

Crabs do not write Jira tickets titled Improve Shell Clarity… yet, but watch this space.

Designers have intent. Designers have taste (but not only designers). Designers can choose to diverge when the environment shifts. Designers can prioritise ethics, accessibility and joy.

Nature does not do joy.

This is our advantage. We are not condemned to converge. We simply tend to, because the conditions make it sensible.

Conclusion: The Crab Test

If several unrelated teams all solve the same problem in roughly the same way, it is not a failure of imagination. It is a sign that the environment has expressed a preference.

The crab is not a cliché. It is a consequence.

And perhaps that is the real lesson. Good design is rarely about imposing novelty. It is about respecting the pressures that shape things. It is about knowing when to let the environment guide you and when to push against it.

Every interface is crawling towards its optimal form. Some just get there faster.

If you enjoyed this piece

Follow me for more articles about design-driven coding, usability, and the messy, wonderful middle ground between aesthetics and logic.

Author’s note:

I am currently deeply interested in using AI to generate both visual and text-based content. I am actively collaborating with AI on multiple platforms to explore my thoughts on what creativity is and is not.

My current approach is to collaborate with AI by using the output as a foundation upon which to build and modify.