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paper: add plain-language parallel version for a basic-ML reader

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A companion accessible manuscript mirroring the full paper section for
section (§1-§13), same argument and conclusions, but assuming only basic
ML knowledge: all population-genetics jargon explained from scratch, a
one-paragraph summary and mini-glossary up front, the five load-bearing
claims and E13 speciation confirmation kept, and the dense
literature-positioning ledger compressed to a pointer back to the full
paper. Honest scoping (grounding-tail limit, merge-headroom condition,
prototype-not-society, open fitness-function problem) preserved.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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# The Evolution of Sex for Artificial Intelligence — the plain-language version
### How ideas from breeding and genetics tell us how to keep AI models improving across generations
*This is an accessible companion to the full paper (`the-evolution-of-sex-for-ai.md`). It makes the
same argument and reaches the same conclusions, but assumes only that you know roughly what a machine
learning model is — that it is trained on data, that training adjusts numbers called "weights," and
that you can fine-tune a model on new data. Everything else is explained as we go. Where the full
paper defends each point against the research literature, this version just tells the story.*
**Giorgio F. Gilestro** · Department of Life Sciences, Imperial College London ·
giorgio@gilest.ro · https://lab.gilest.ro
---
## The one-paragraph version
If you train an AI model on the output of earlier AI models, over and over, it rots: rare knowledge
disappears and everything drifts toward a bland average. This is a known problem ("model collapse"),
and it turns out to be *exactly* the same math that describes how small biological populations lose
rare genes by chance. That is bad news, but it comes with good news: biology already discovered the
cure for this kind of rot hundreds of millions of years ago. The cure is **sex** — making offspring by
*combining* several parents instead of copying one. This paper takes ninety years of genetics about
*when and why sex beats cloning* and reads it as an engineering manual for building AI that keeps
getting better across generations instead of decaying. Along the way it produces concrete, testable
rules — including a surprising one about *how* to combine models ("merge, don't average"), and a limit
("models can drift so far apart they can no longer be usefully combined at all"). We back the argument
with small, fully reproducible experiments and a first test on real language models.
---
## A few words you'll need
- **Model collapse** — what happens when you train models on the output of earlier models, again and
again: rare cases vanish, everything gets blander. The central disease this paper is about.
- **Fine-tuning / specialising** — taking a trained model and training it a bit more so it gets good at
one specific thing.
- **Model merging** — combining two or more trained models directly, by mixing their weights, to get
one model — *without* retraining. Think "breeding two models" rather than "teaching a third."
- **The tail** — the rare stuff. Common knowledge is the "head" of the distribution; unusual cases,
rare facts, and edge behaviours are the "tail." Collapse eats the tail first.
- **Grounding** — mixing some real, verified data from the actual world into training, instead of only
model-generated data. The reality check.
- **Genetic drift** (from biology) — in any finite population, rare gene variants can vanish purely by
chance, because not every individual reproduces. This is the biological twin of model collapse.
- **Recombination / sex** (from biology) — making a child by combining pieces of more than one parent.
The opposite of cloning (**asexual** reproduction).
---
## 1. A society of AIs across *time*, not just space
When people imagine "many AIs working together," they usually picture teamwork in the *moment*:
several specialist agents side by side, splitting up a job. This paper is about a different direction:
**time**. Not AIs that cooperate right now, but AIs that pass knowledge down across **generations** —
each new model starting from what the previous ones learned, the way each human generation inherits
the accumulated knowledge of the last and adds a little.
The key event, then, is **reproduction**: making a new model out of older ones. A single model, like a
single person, eventually stops improving. A *lineage* — a chain of models across generations — does
not have to. Civilisation isn't smart because any one person is; it's smart because knowledge
accumulates. The whole question of this paper is: **how do you make one AI model out of older ones,
without the knowledge rotting on the way down?** That's exactly where it can go wrong.
(This corner of AI is suddenly busy: several 2025–2026 research projects build populations of models
that improve over rounds, and "model merging" has become a small industry that already borrows words
like crossover, mutation, and mate choice. What's missing, and what this paper supplies, is the actual
*theory* behind those borrowed words.)
## 2. Why today's models can't do this
Today's large models have no life cycle. A model is trained once, at huge expense, then **frozen** and
shipped. It does not learn from the people who use it. "Learning" and "doing" are two separate eras
with nothing connecting them.
There's a real reason for the freeze: if you keep training a neural network on new things, it tends to
overwrite what it already knew. This is called **catastrophic forgetting**, and it's been a known
problem since the 1980s. Freezing dodges it by refusing to learn at all. But a lineage needs the
opposite of a frozen model: it needs members that keep learning through their working lives and then
pass on what they gained. So step one is a model that can *grow safely.*
## 3. A model that grows without forgetting
The trick is to stop overwriting. Keep the model's original core frozen and untouchable, and bolt each
new skill onto *extra* capacity added beside it. In practice this is what small add-on "patches" like
**LoRA** already do: the big pretrained model stays fixed, and you train a little attachable module for
each new skill. If the core is never altered, forgetting it becomes impossible by construction — not
just unlikely.
There's even a rough brain analogy: we have a fast memory (the hippocampus) that grabs an experience
immediately, and a slow memory (the cortex) that absorbs patterns gradually, usually while we sleep.
The AI version is clean: the prompt is short-term memory, a database is fast memory, the trained
weights are slow memory, and a periodic "consolidation" step moves knowledge from fast to slow.
One consequence matters a lot: because this kind of model only ever *adds* capacity, it eventually
fills up. In most designs that's a problem. Here it's a feature — read on.
## 4. "Full" means grown up, not broken
Here's the pivot. When a model that can only add capacity finally fills up, it hasn't failed. **It has
matured.**
Think of the capacity limit as a life stage. A model is *born* as a freshly trained base — its general
education. It has a *working life*, picking up specialised expertise on the job. And it reaches
*maturity* — the point where it has learned about as much as one working life in its niche can teach.
Maturity isn't the end of usefulness; it's the moment the model is most worth learning *from*. So
maturity is the signal to **reproduce**. The capacity ceiling that every other design fights becomes,
here, the clock that times the generations.
Everything now depends on *how* that reproduction happens. This is the heart of the paper.
## 5. Copying rots; combining climbs
Suppose a mature model just teaches a fresh one, and that one teaches the next, and so on down the
line. It's the obvious design — and it fails, for the same reason in AI and in biology.
**In AI terms:** training each generation on the previous generation's output is the exact recipe for
**model collapse**. The model forgets the improbable, loses the rare cases (the tail) first, and drifts
toward its own most common output. And here's the nasty part: the thing that makes teaching-a-student
*useful* — "keep the general, drop the quirky" — *is* the same act that deletes the tail. The operation
you want and the operation that kills the lineage are the same move.
**In biology terms (and it's literally the same math):** picture a model's knowledge as a big bag of
items — facts, skills, behaviours — in certain proportions. One generation is: draw a finite sample
from the parent, and rebuild the child from that sample. That "finite sample" step is *identical* to
**genetic drift** — the way rare gene variants vanish by chance in any finite population. This isn't a
loose analogy; it's the same century-old equations (the Wright–Fisher model), which is why we can
check our simulations against them exactly. Rare items go extinct first, about ten times faster than
common ones — precisely what drift predicts.
And copying one teacher is **asexual reproduction** — cloning. Biology already knows the fate of a
lineage that only ever clones and never combines: it piles up damage it can never undo, a one-way
decline called **Muller's ratchet**. *Muller's ratchet is model collapse.* Naming it that isn't just
poetry — it tells us where the cure is, because biology already solved this.
Two ingredients turn the rot into a climb. Both are things nature does.
**Ingredient one: don't reproduce "dry."** Collapse only happens to a lineage fed *nothing but* its own
output. Mixing in some **real, verified data from the world** — we call this **grounding** — stops it. In
our small experiments, grounding is shockingly cheap: even a few percent of real data keeps most of the
diversity alive indefinitely. But we found an honest limit we didn't expect: grounding can't save the
*very rarest* items at any affordable cost — protecting something of rarity *p* needs a real-data budget
that grows like 1/*p*. Grounding rescues diversity cheaply, but not the deepest tail. Something else has
to do that. That something is sex.
**Ingredient two: reproduce sexually.** Instead of copying one parent, build each new model by
**combining several** — a sexual birth, not an asexual one. AI already has a tool for this: **model
merging**. Why does it help? If several parent models each specialised on *different* things, each one
kept alive rare knowledge the others lost. A combined child inherits the **union** of what its parents
kept — not the tail-thinned *average* of a crowd of near-identical clones. And here's the point that
turns sex from a mere safety net into the engine of the whole thing:
> **A child combined from complementary parents can be *better than any of its parents*.**
Geneticists call this the **Fisher–Muller effect**: recombination gathers, into one individual,
good variants that arose separately in different lineages — so the child has a combination none of the
parents had. Our simulations show exactly this: combining specialist models that each mastered
different skills produces a model that climbs toward the *best possible* combination — one no single
parent had — while the best single parent, and the plain average of all of them (a "**model soup**"),
both level off well below. This is the paper's core claim in one line: **copying can only recover a
ceiling; combining can break through it.**
And it's not just simulation. In a first test on real language models — three small Qwen models, each
fine-tuned on a different family of tasks, then merged and graded by an automatic checker — **the merge
beat every single specialist**, overall and on every task family. The Fisher–Muller effect, in real
weights.
That same test pinned down a subtle rule about *how* to combine models:
> **"Merge, don't average" — but only when there's room to lose.**
Keeping each parent whole and **routing** each question to the right specialist beats crudely averaging
them together — *but only when the task is hard enough that averaging actually damages something*. On
easy tasks, a strong model's plain average is already about as good as possible, so the crude soup is
fine. On hard tasks, averaging waters down a hard-won specialist so badly the blend falls below even the
best single parent — and the smarter "keep-them-separate-and-route" approach wins big. So the rule is
precise: **the fancy combining tricks help in exact proportion to how far the plain average is from the
best you could achieve.** A practitioner needs to know this before spending compute on the fancy version.
Two honest caveats, and both are actual findings, not hand-waving:
**Sex can backfire.** When the parents' skills aren't cleanly separable but *tangled together* — when
skill A only pays off if skill B is also present (biologists call this **epistasis**) — blindly
combining two good models can produce a *worse* child, because combining breaks apart a package that
only worked as a whole. Biologists call this **outbreeding depression**, and we reproduce it: on
"tangled" problems, naive merging drops the child below its parents, and the more you mix, the worse it
gets. The design rule: *combine freely when skills are independent; combine sparingly and carefully when
they're tangled.*
**AI can do sex better than biology can.** Biology is stuck with two parents, mating more or less at
random, and can't inspect a child before it's born. AI has none of those limits. It can combine **many**
parents at once; it can **choose** which parents to combine, for complementary skills; and it can
**generate many candidate children and keep only the best**, testing them against reality before
committing. We call this **directed sex**, and in our simulations it turns the outbreeding-depression
disaster into a reliable win: where blind combining collapses on tangled problems, directed combining
matches or beats the best parent every time. The real-language-model test shows the same where it can:
breeding many merged offspring and keeping the one that scores highest beats the plain soup on hard
tasks. This is a genuine advantage of *engineered* reproduction over the biological kind, and it's one
of the more useful ideas in the paper.
So §5 in one breath: copying is asexual and rots (Muller's ratchet = model collapse); the cure is to
**ground** every birth in reality and to reproduce **sexually**, combining many complementary parents;
and because AI's version of sex can use many parents, chosen mates, and pre-screened offspring, it's
not just insurance against collapse — it's an engine that makes children better than any parent.
### The limit of sex: models can drift too far apart to merge
Sex has a limit, and it's the sharpest new prediction here. Combining parents works because they're
variations on a shared background. Push two lineages far enough apart and their combination stops being
viable. In biology this is **speciation** — two populations become separate species that can no longer
interbreed. The genetic mechanism has a name (a **Bateson–Dobzhansky–Muller incompatibility**): a change
that arose in lineage A and a change that arose in lineage B are each harmless on their own, but their
*combination* — which neither lineage ever tested — is broken in the hybrid. A merged model is exactly
such a hybrid. So the theory predicts a specific trajectory as two models drift apart: **they merge
fine → merging starts to hurt → merging becomes useless.**
We built this as an explicit model and confirmed the predicted curve. Three things come out of it:
1. **There's a cliff, and epistasis moves it.** The point where merging fails isn't fixed — it comes
*earlier the more tangled (epistatic) the skills are*. This is a distinct, testable claim:
**at the same amount of drift, whether two models can be merged depends on how tangled their skills
are, not just on how far apart they are.** The existing AI tools for predicting merge success only
measure distance/geometry — they don't have this axis.
2. **It snowballs.** The number of incompatibilities grows with the *square* of the drift, so merge
quality doesn't fade gently — it falls off a cliff. Drift is punished faster than it accumulates.
3. **The design rule:** before merging, weigh how far apart the models are against how tangled the skills
are. Past the cliff, don't merge — **route** instead (keep the specialists separate and pick between
them).
We also did the experiment a skeptic would demand. A known objection: "your 'incompatibility' is just a
loss barrier, and those are famous for being fake — two networks can learn the *same* function but store
it in a shuffled internal order, which *looks* like incompatibility until you line their neurons back up
(a technique called **Git Re-Basin**)." So we tested it directly in real trained networks. We trained
pairs of small networks, merged them, and measured the merge damage *before and after* re-aligning their
neurons. The result is clean:
- Two networks trained on the **same task** but from different random starts: big apparent merge damage,
but re-aligning removes **~98% of it**. That's the fake kind — same skill, shuffled order. (This also
proves our alignment tool works.)
- Two networks trained on **conflicting tasks**: big merge damage, and re-aligning removes **none of
it**. That's the *real* kind — genuine incompatibility, not a bookkeeping artifact. And it can't be
waved away as "you just didn't align them well," because the exact same tool cleaned up the first case.
Sweeping from "no conflict" to "total conflict" traces a smooth **incompatibility cliff** in real
weights — confirming the prediction. So the speciation effect is real, not a relabelled artifact.
One question is left hanging, and the rest of the paper is about it: combining preserves *what the
parents kept* — but **who decides what each parent keeps, and which children are worth keeping?**
## 6. Don't design the selector — evolve it
There are two ways to answer that question, and the first one is wrong. We could try to hand-write the
rule for "what knowledge to keep and pass on." But nobody actually knows that rule. "Keep the general,
drop the specific" sounds wise until you ask *which* generalisations, in *which* domain, at *which* level
of detail — and it falls apart. This is the deepest gap in the whole scheme, and you can't fill it by
decree.
The second answer is the one nature used: **don't design the selector — let it evolve.** Let different
models carry different *policies* about what's worth keeping and combining. Let the policies that produce
strong children spread, and the policies that produce weak children die out with their lineages. What the
lineage considers *important* — its "taste" — is discovered by selection, not imposed by us.
So **two things get inherited, on two channels.** The *content* — the actual knowledge — is passed down
directly (this is the "Lamarckian" part: inheriting things acquired during a lifetime, which biology
forbids for genes but culture allows for ideas). The *selection policy* — what to keep, who to breed
with, which children to screen for — is *itself* inherited, varies between models, and survives in
proportion to how well it works. That second channel is Darwinian. The system is both at once: it
inherits *content* like culture, and selects *policies* like evolution.
And it closes neatly: Darwinian selection needs a pressure — something that decides which policies win.
That pressure is already in the design. What tells a lineage its taste was good? Whether its children
succeed *against reality*. The reality check that stops collapse (grounding, §5) and the fitness signal
that guides the evolving taste turn out to be the **same thing**, seen from two angles.
## 7. The big danger: what you measure is not what you want
Adding selection adds selection's classic trap, and it's dangerous enough to sink everything if ignored.
Evolution optimises, ruthlessly and without foresight, for exactly what you *measure* — never for what
you *meant*. (In ML you know this as reward hacking or specification gaming; economists call it
Goodhart's law.) Get the fitness measure a little wrong and the lineage will exploit the gap more
cleverly than any rule you could write.
For a *knowledge* lineage there's a particularly nasty version. The natural way to measure how "good" an
idea is might be *how well it spreads* — but a false-but-persuasive idea spreads beautifully. Human
culture is full of highly contagious nonsense; confident wrongness routinely beats careful accuracy. Let
selection loose on models without care and it will breed a lineage that is fluent, compelling, and
**wrong** — model collapse with an optimiser actively steering toward the cliff.
Only one thing makes fitness track *truth* instead of *appeal*: **being judged against a reality that
can say no.** Fitness has to mean "did this knowledge correctly predict what the world actually does when
you act on it" — not approval, not fluency, not a gameable benchmark score. This is why the reality check
matters twice: it's both the anchor that stops passive collapse *and* the only thing that keeps the
evolving taste honest.
The second danger is **everyone converging to the same thing**, and avoiding it takes work at two levels,
because selection can only preserve variety that already exists — variety first has to be *supplied* and
then *kept*.
- **Supply.** A lineage that only learns from the accredited elite has a monoculture for a source — the
"top" experts are, by definition, the ones who won the consensus. So the system must deliberately learn
from **outliers and heretics** too — not out of fairness, but because diverse starting material is the
raw fuel for everything downstream.
- **Preserve.** Even with varied input, plain "keep the best" selection converges — it stampedes toward
the single current champion and wipes out the rare specialists. The fix is well known:
**quality-diversity** selection, which rewards being *good* **and** being *different* at the same time,
keeping complementary specialists alive. In our simulations this is decisive: greedy "keep-the-best"
collapses diversity almost immediately and gets stuck on a mediocre answer, while quality-diversity
keeps the very specialists that sexual combining then needs as parents.
The two levels meet at reproduction: multi-parent combining is the *vehicle* that carries the preserved
diversity into the next generation. Supply the variety, preserve it, recombine it — remove any one and
the lineage collapses onto its own first guess.
## 8. A society needs institutions, not just experts
One requirement is easy to miss and fatal to skip. The easy part of a society is having specialists. The
*hard* part — which human civilisation took millennia to build — is the **institutions that let fallible
specialists combine without each re-checking everything**: reputation, replication, credentials, and
above all **peer review**. These are error-correction systems, and they exist because a group of
unreliable experts left to reinforce each other is *more* wrong than any one of them alone.
This is exactly where today's multi-agent AI fails: put several models in a room and they tend to agree
sycophantically and confabulate together, because they have all the specialisation and none of the
institutions. A real multigenerational society has to specify not just how models learn, reproduce, and
get selected, but how they *check each other* — how a wrong model loses standing *before* its error gets
merged into its children and inherited.
## 9. The lineage must stay open to reality
However many generations deep it goes, a society of models shares one hard limit: it has only ever
*read*. Its entire inheritance is a record of things that were *said*. It lives on the bottom rung of
what causality researchers call the ladder — **observation** — and no amount of reading ever reaches
**intervention**. Watching doesn't tell you what would happen if you *acted*; correlation isn't causation
at any scale.
Only intervention — actually reaching out and changing the world to see what happens — climbs that
ladder, and a language model can't intervene. That's what humans and their instruments provide, and the
gift isn't "truth," it's **constraint**: reality's unique power is that it can say **no**. Text just
offers more opinion; an experiment delivers a refusal no consensus can overturn. As before, that refusal
does double duty: it stops collapse *and* keeps the evolving taste selecting for truth over persuasion.
Two honest riders. First, the human reality signal is *dirty* — warped by publication bias, incentives,
and the occasional fraud — which is exactly why the error-correcting institutions of §8 have to sit at
the human–machine boundary. Second, humans are the *current* supplier of intervention, but the hands-on
half is being automated (robot labs already run their own experiments). What looks durable in the human
role isn't the hands — it's the **choice of what to test and which refusals matter**.
## 10. Why this is affordable
A practical fact turns this from daydream into buildable proposal: **it almost never re-pays for the one
genuinely expensive thing in AI — training a model from scratch.**
Training a foundation model from scratch costs a fortune in data and compute. This design does none of
that per generation. Every model is *born* from an existing open model that already paid that cost;
specialising one is a small patch trained in hours on a single consumer GPU; running the society is
ordinary use; and reproducing — merging parents into a child — can be done directly on the weights with
*no retraining at all*. Selection costs more (you have to run populations and discard the losers), but
that's a multiplier on an already-cheap unit, not on a from-scratch budget.
The economics only work with **open-weight** models — for practical and legal reasons at once. You have
to be free to inspect, modify, and redistribute the weights, and most proprietary licences forbid using
a model's output to train another (which is exactly what reproduction here does). That's not ideology —
it's a structural constraint, and a democratising one: it puts the whole thing within reach of a single
lab.
## 11. Can it grow forever? Baking knowledge back into the base
One thing we quietly assumed: can the lineage accumulate *without end*? The individual model is
bounded — that's the clock. But the lineage looked unbounded, each generation starting a step ahead.
Look closer and a second budget also fills up.
Every new model is a clean base plus an inherited pile of *soft* patches — the acquired knowledge carried
in add-on modules rather than baked into the core. Those patches are what make the lineage
multigenerational — but they're not free: they slow the model down, and past some depth they're better
*consolidated* than carried. The lineage matures too.
The fix is the same operation, one level up. When a lineage's acquired knowledge has proven stable across
enough generations, **re-mint the base**: bake all those accumulated patches into the *weights* of a
fresh from-scratch-scale model — a new base that is *born already knowing* what took many generations to
learn in patches. The soft budget resets; the next era starts from a higher floor. What was hard-won and
*learned* becomes cheap and *built-in*. (Biologists have a name for acquired traits that eventually
become innate: the **Baldwin effect**.)
Three honest riders, because this is the most consequential step:
- **Cost.** This is the one step that re-pays part of the from-scratch bill — the exception to §10. It's
bearable only because it's *rare*, spread thin over many cheap generations.
- **Irreversibility.** Until now, one thing was always recoverable — the original clean base, whose lost
rare knowledge you could restore just by reloading the file. Bake the current lineage into new
permanent weights and that escape hatch closes: if the lineage had been quietly collapsing, re-minting
*freezes the collapse in place* and throws away the one uncollapsed reference that could have caught it.
In our experiments this happens exactly as feared — and a cheap safeguard prevents it: **only re-mint
while the lineage is provably healthy and diverse**, never as a rescue for one already drifting.
- **Branching.** Different labs will re-mint on different criteria and produce different bases; the
lineage branches. That's not a bug — it's the tree of life, and it's exactly what open weights make
possible.
So can it grow forever? **Yes — but only because it forgets and consolidates at every level, including
the base.** Nothing is stored without limit anywhere. Unbounded growth of *capability* is bought with
*bounded* storage plus periodic consolidation.
## 12. One idea at four speeds
Step back and it all resolves into a single process running at four nested speeds. The **downward**
motion is transmission — passing hard-won knowledge down:
1. **Within one model, over its working life:** experience moves from fast memory into slow, durable
weights, without catastrophic forgetting.
2. **Between generations, at maturity:** mature models reproduce, recombined into a fresh one.
3. **Across many generations:** each inherits the compressed achievements of the last and adds a little.
4. **Across eras:** a proven lineage's accumulated patches get baked into a re-minted base, becoming
innate.
The first and last are the *same operation at opposite ends of the scale* — fast/soft memory
consolidating into slow/hard memory — one running overnight inside a single model, the other across an
era inside a whole society. The **sideways** motion is selection — acting across the population at every
speed, on the policies that decide what gets passed on, with reality as the judge and diversity kept
alive so the specialists survive.
Three rules govern all of it: **reproduce by combining, not copying, or you rot; keep the disagreements
and surprises, or you converge; and anchor fitness to a reality that can say no, or you drift toward
whatever is merely convincing.**
## 13. What we actually built, found, and left open
We didn't just argue this — we built small, fully reproducible models to test it, plus a first bridge to
real language models. Here's the shape of the evidence (a separate document has the numbers).
**What we built and found:**
- **An exact account of collapse.** Because generational training *is* the genetic-drift process, we can
check our simulator against century-old formulas — and it matches to a fraction of a percent. Collapse
isn't argued by analogy; it's derived.
- **Grounding is cheap — but has a limit.** A few percent of real data keeps most of a lineage's
diversity alive indefinitely — but not the very deepest rare cases, which need combining. This is what
makes a continually-learning society economically realistic rather than a data-hungry fantasy.
- **"Merge, don't average."** Combining several teachers by *averaging* their outputs — the obvious
thing, and what a "model soup" does — mathematically cancels the benefit of having several teachers. A
*merge* that keeps each item's strongest source realises it. Most current multi-model setups get this
wrong by default.
- **Collapse and its cure in real networks, and on real images.** We reproduced the same effects in small
neural networks and in a generator of handwritten digits (MNIST): a model trained on its own output
collapses to a single blurry digit, while a little grounding keeps all the styles alive. Honest
wrinkle: real networks *smooth* things over, so the naive diversity metric can mislead — the right
measure is distance-from-truth.
- **Sex that beats the parents — and when it doesn't.** In simulations, combining complementary
specialist models produces a model better than any parent (Fisher–Muller), climbing toward the best
possible combination as you add more, more-diverse parents — while averaging and best-single-parent
level off below. On *tangled* problems, blind combining instead produces below-parent children
(outbreeding depression) — and *directed* combining (choose mates, screen offspring, many parents)
reliably fixes it.
- **The combining claims, in real language models — with a sharp condition.** Merging fine-tuned Qwen
models (up to 7B on a GPU cluster) produces a generalist that beats every specialist parent; and
keeping parents separate and *routing*, or *breeding and screening* offspring, beats the plain average
— *but only when the task leaves room to lose*. On easy tasks the plain average is already at the
ceiling and the tricks add nothing; on hard tasks the average dilutes a specialist below even the best
single parent, and the smarter operators win clearly. This is a prototype (three task families, one
run), so we read it as *signs, not exact numbers* — the *whole grounded society* on a language model is
still the open step.
- **The whole society, and why every part is needed.** In a population evolving on a "reality" landscape,
the full system — grounding + combining + preserved diversity — climbs to the top while keeping its
specialists. Remove *grounding* and it collapses into a confident, wrong consensus (a direct analogue
of training on the internet's growing pile of AI-generated text); remove *combining* and it gets stuck;
remove *diversity* and it converges too fast to a worse answer. Each removal breaks differently; only
the whole thing climbs.
**What's borrowed vs. what's ours.** We're careful about credit because the area is crowded. **Already
known (and we claim none of it):** that model collapse is genetic drift; that a merged model can beat its
parents; that decorrelated parents merge better; that naive averaging is worse than smarter merges; that
populations of self-improving models can climb. **What's genuinely new here** is the *theory* those
results have outrun — a real population-genetics of sex for model societies, which *predicts* rather than
just *observes*: the "merge, don't average" law, Fisher–Muller as the reason children beat parents,
outbreeding depression on tangled landscapes (turning "when does merging help?" into something the
problem's structure predicts), grounding as a migration-vs-drift balance with a critical real-data
fraction, directed sex as AI's distinct advantage, the whole integrated society whose parts are shown
*jointly necessary* — and, newest of all, **model speciation**: the account of *when two models are too
far apart to merge at all*, confirmed in real weights.
**What's still open — honestly.** We fill the old hole (what to select) by *evolving* the selector
instead of designing it — but the hole *moved* rather than closed, and the new one is harder: **the
fitness function.** What reality-anchored measure selects for *truth* without also selecting for
*persuasion*, given that in our own species the two have been at war for the entire history of ideas?
Alongside it: the *institutions* that let models correct each other before error is inherited (§8), which
we don't solve; and the *calibration* of all the knobs the experiments left open — how many parents, how
complementary, at what ratio of inherited-to-real data, how healthy a lineage must be before its
knowledge is safe to make permanent. These are at least *measurable*, which is the difference between an
open problem and a hole. And the biggest gap: the *combining* claims now hold in real language models,
but the *society* — the grounded, diversity-preserving, continually reproducing loop — does not yet. The
real test is to build that whole thing out of actual open language models and see whether all the signs
survive. **The operators, checked; the living society, next.**
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*For the full argument, the literature it's positioned against, the exact predictions, and the
references, see the complete paper: `the-evolution-of-sex-for-ai.md`.*