Dollo’s Law
You can reverse a decision, but you can’t reverse everything that happened because of it, so organizations can revisit an old design, but they can’t return to an old state.
What Is It?
Dollo’s Law of Irreversibility, named for French-Belgian paleontologist Louis Dollo, states that evolution doesn’t run in reverse: an organism cannot return, even partially, to a previous evolutionary state already realized in its ancestry. Modern biology treats it as a strong tendency rather than an absolute rule, but the core mechanism holds: evolution changes many interconnected systems simultaneously, so recreating a previous state would require recreating all of those interactions at once, not merely reversing one visible change. The deeper point is that history is cumulative, every change alters the conditions under which the next change happens, so undoing the most recent step doesn’t undo the history that step was built on.
Why Does It Matter?
Leadership teams routinely announce a return to “the culture we used to have,” rehire a founder, re-adopt old software, or restore old reporting lines, on the assumption that the old arrangement is still there, waiting to be reactivated. It isn’t. What actually made it work wasn’t the org chart or the tool, it was an ecosystem: specific people, specific trust relationships, specific market conditions, specific institutional memory, accumulated over time and now gone. Two organizations can have identical org charts, one that evolved into it over ten years and one built yesterday, and still not be the same organization, because history is part of what makes them different. The org chart survived. The organization didn’t. What gets rebuilt is a new structure wearing the old one’s name.
What Changes Once You See It?
You stop treating “let’s go back to the old way” as a simple, low-risk default, and start treating it as its own design decision, one built from today’s conditions rather than a nostalgic reconstruction of yesterday’s, and justified on its own merits rather than assumed to be a safe return to known ground.
You also start being honest, out loud, that the rebuilt version is new, which changes how much scrutiny it gets.
Common Misunderstandings
- It isn’t a claim that old structures can never inform new ones. A past arrangement is legitimate, useful input, the point is that “restoring” it is actually building something new that’s informed by it.
- It doesn’t mean change is always for the better, or that old structures were flawed. It’s a claim about the mechanics of reversal, not a verdict on which structure was superior.
- It isn’t an argument against reversing bad decisions. Sometimes reversing course is exactly right, the point is that the reversal begins from today’s organization, not yesterday’s.
- It isn’t absolute even in biology, some traits do reappear through different mechanisms. The organizational lesson is about how unlikely a literal rewind is, not that it’s categorically impossible.
Diagnostic Question
Which of the conditions that made the old system work still actually exist?
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Field Notes
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Origin
Named for French-Belgian paleontologist Louis Dollo, who proposed the principle of irreversibility in evolution in 1893.