The Egg That Started as Skin

Take a cell from the inside of your cheek, or a drop of blood, or a fleck of skin. It is a finished thing. It has spent its whole existence being unambiguously you, a somatic cell with a fixed job, nowhere in its future the ability to become a person. Now imagine coaxing it backwards, past its own job, past its own specialization, all the way to the state it was in a few days after you were conceived, and then forward again down a completely different road until it becomes an egg. A cell that could, in principle, be fertilized and grow into a human being.

That is not a thought experiment anymore. In the last two years, labs on two continents have made early human eggs starting from ordinary body cells. The starting material for a human being was, for the first time, a piece of skin.

The field has a bloodless name, in vitro gametogenesis, IVG for short. It deserves a louder one, because if it works it will be the largest change in human reproduction since IVF, and possibly since the thing itself. And the part almost no one is saying out loud is that the science is the smaller story. The larger story is how it happened, because it tells you something about the only force on Earth that reliably turns the impossible into the routine.

What actually happened, and what did not

Let me be precise, because precision is the whole point with something this easy to hype.

In September 2025, a team led by Shoukhrat Mitalipov at Oregon Health & Science University reported, in Nature Communications, that they had made functional human eggs using nuclei taken from skin cells. Their method is a piece of biological judo. They took a donor egg, stripped out its nucleus, and slipped in the nucleus of a skin cell. The egg’s cytoplasm, the machinery in the cell around the nucleus, then did something remarkable: it induced that skin-cell nucleus to throw away half of its chromosomes, the way a normal egg does when it matures. The team named this new kind of cell division mitomeiosis, a blend of ordinary cell division and the special chromosome-halving of egg and sperm formation.

They made 82 eggs this way. And then, being honest scientists, they told everyone what was wrong with them. The chromosome-halving was messy. Many eggs ended up with the wrong number of chromosomes. As Mitalipov put it, the technique “partially works, and partially doesn’t.” This is a proof of concept, not a baby, and the distance between those two things is the entire subject of this essay.

Running in parallel is a different road, taken by a company called Conception. Instead of borrowing a donor egg’s machinery, they are trying to grow the machinery itself. They take blood cells, reprogram them into stem cells, and then coax those stem cells to build an entire miniature ovary in the lab, because an egg does not mature in isolation. It matures inside an organ, surrounded by supporting cells sending the right signals in the right order. Conception’s bet is that you cannot shortcut the organ. You have to rebuild the neighborhood, not just the house. They have reported reaching early human egg cells along this path.

To see why this is a species-level event and not just a clever lab trick, hold two facts next to each other. First, a woman is born with all the eggs she will ever have, and they decline in number and quality with age; that clock is the hard biological constraint under most infertility. Second, you make new skin and blood cells constantly, your whole life. IVG proposes to convert the second, renewable thing into the first, scarce one. It aims to take the one part of the body that does not renew and make it renewable from the parts that do.

The real story is the relay

Here is the thing I cannot stop thinking about, and the reason this belongs in a series about evolution rather than a science-news roundup.

Nobody did this.

I mean that almost literally. There is no lone genius in this story, no single eureka in a single skull. What made a skin cell into an egg was a relay race run across roughly twenty years, several countries, and a chain of people most of whom never shared a lab.

The first leg was run in Kyoto in 2006, when Shinya Yamanaka showed that an adult cell could be reprogrammed back to an embryonic-like state with just a handful of molecular switches. Induced pluripotent stem cells, iPS cells. It won a Nobel Prize in 2012 and it is the foundation the entire field stands on, because it is the move that turns your skin into raw clay.

The second leg was run in Japan again, by Katsuhiko Hayashi and Mitinori Saitou, who spent years learning to walk that clay forward instead of backward. By 2016 they had made functional eggs from mouse stem cells, entirely in a dish, and those eggs produced live, healthy, fertile mouse pups. In 2023 Hayashi reported something stranger still: eggs grown from the cells of male mice, opening the door, in mice, to two genetic fathers.

The third leg is the human one, Mitalipov’s mitomeiosis and Conception’s mini-ovaries, each building directly on everything the earlier runners handed them. Each team published, or presented, so the next could check the work and take the baton. Hayashi, on the other side of the world, is quoted assessing the human result: a significant breakthrough in halving the human genome. The competitor grades the paper. That is not a bug in science. That is the mechanism.

This is what science actually is, stripped of the mythology. Not a flash of insight but a compounding ledger, where each entry is written so that a stranger can audit it, build on it, and pass it forward. It is the closest thing our species has to a collective memory that gets smarter over time. Evolution took four billion years to invent the egg by blind trial and error. Human science reverse-engineered a new way to make one in about two decades, because unlike evolution it can share what it learns and does not have to rediscover the same thing twice. That is the superpower. Not any one brain. The protocol for combining them.

Now simulate the future

A tool this fundamental does not have one future. It has a fork. So let me do what an engineer does with any powerful new system before trusting it: run the scenarios. Here are the three best outcomes and the three worst, as concretely as I can make them, because “it could be good or bad” is a cop-out and the specifics are where the truth lives.

The three ways this goes right

Infertility comes unstuck from age and luck. The deepest promise is also the simplest. If a healthy egg can be made from a blood draw, then the thing that limits most fertility, the number and quality of a person’s own eggs, stops being destiny. A cancer survivor whose treatment ended their fertility. Someone with premature ovarian insufficiency at 30. A woman who spent her twenties and thirties on everything except a pregnancy she now wants at 44. Today those stories often end at a wall. IVG proposes to move the wall, with no hormone injections and no surgical egg retrieval, the two most brutal parts of IVF. For a huge number of people this is not a luxury. It is the difference between a genetic child and none.

Two people can have a child related to both of them, whatever their biology. Because IVG makes a gamete from any body cell, the ancient requirement of exactly one egg-maker and one sperm-maker starts to loosen. Hayashi’s 2023 mouse work, eggs grown from male cells, is the proof of principle that this is not fantasy, at least in animals. Extended to humans someday, it would mean a same-sex couple could have a child genetically tied to both of them, rather than to one of them and a donor. An entire category of family that biology simply forbade becomes, in principle, possible. Whatever you feel about it, notice the magnitude: a constraint as old as sexual reproduction, quietly rewritten.

Inherited disease gets screened out at a scale that changes medicine. IVF today yields a handful of embryos, so screening them for genetic disease is real but limited; you choose from what little you have. Make eggs abundant and you can generate many embryos and screen them properly, dramatically improving the odds of a child free of a devastating single-gene disease that runs in a family. And the same lab pipeline that produces the eggs is a microscope on the earliest, most hidden days of human development, the stretch we have never been able to watch. The knowledge spillover, into miscarriage, into developmental disease, into basic biology, could dwarf the fertility application itself.

The three ways this goes wrong

We make sick children by moving too fast. This is the near and obvious danger, and Mitalipov’s own honesty is the warning label: the eggs come out with the wrong number of chromosomes. In an embryo that usually means it does not implant, or it miscarries, or, in some cases, it produces a child with a serious chromosomal disorder. The pressure to skip ahead will be enormous, because the customers are heartbroken and the demos look magical. But “partially works” is precisely the failure zone, the place where a technology is good enough to produce a pregnancy and not yet good enough to guarantee a healthy one. Rushing from 82 flawed eggs to a live birth is how you turn a triumph into a tragedy.

Reproduction turns into a selection pipeline, and variation narrows. Follow the abundance to its logical end. If a couple can make not five embryos but five hundred, choosing among them stops being “avoid this fatal disease” and slides toward “optimize this whole list of traits” as our ability to read traits from DNA improves. No edits, no headlines, just selection, quietly, at scale. The risk is not a single monster; it is a slow convergence, millions of independent choices all reaching for the same fashionable few traits, thinning the genetic variety that has been our species’ entire insurance policy against a future we cannot predict. Evolution’s messy diversity is not a bug we get to clean up. It is the hedge that keeps a species alive when the environment changes.

The hype outruns the biology, and the money makes it worse. This field has everything a bubble loves: a miracle narrative, desperate and wealthy customers, and serious capital chasing it. That is the exact recipe that produced Theranos, a company that sold a blood-testing dream years ahead of a working machine. Fertility is more emotionally charged than a blood test and harder to verify from the outside. The temptation to announce a breakthrough by press release, to sell hope on the strength of a proof of concept, to let a valuation get ahead of a verified healthy birth, will be intense. The most likely near-term harm is not a designer-baby dystopia. It is ordinary people paying real money for a promise the science has not actually kept yet.

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The same capability ends age-based infertility in one future and becomes a manufacturing line in another. The biology does not choose the branch. The rigor around the biology does.

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The engine is also the guardrail

Notice something about all three bad outcomes. Every one of them is a failure of rigor, not a failure of the science. Sick children come from skipping the safety work. A selection pipeline runs on treating a probabilistic trait score as if it were a guarantee. The hype bubble inflates precisely when claims stop being checked. The danger is never the knowledge itself. It is knowledge moving faster than verification.

Which is the quiet, almost unreasonable good news. The same force that produced this, open, collaborative, adversarial science, is also the only thing that reliably catches its failures. Mitalipov’s team publishing the flaws instead of burying them. Hayashi grading a rival’s result from another continent. The replication, the peer review, the boring insistence that an extraordinary claim be reproducible by someone who wants you to be wrong. That machinery is slow and unglamorous and it is the entire immune system of the enterprise.

We have a control case for what happens when someone steps outside it. In 2018 a scientist edited the genomes of twin girls in secret, announced it after the fact, skipped the scrutiny, and produced a scandal that set his whole field back and sent him to prison. I wrote about that moment as the day we picked up the pen on our own evolution. The lesson was not that the knowledge was evil. It was that knowledge divorced from the collaborative checking process is where the real monsters live. The secret lab, not the shared one, is the dangerous place.

So when the next headline lands, and it will, promising a baby from a skin cell, here is the only question worth asking. Not “is it amazing,” because it is. Ask: has it been shared? Published, replicated, checked by people who would love to prove it wrong, and survived that? The gap between “announced” and “verified” is where every one of the bad futures hides, and it is a gap you can learn to see.

We spent four billion years as something evolution wrote without a plan. In the space of one human lifetime we learned to read the code, edit it, and now to manufacture the very cell that carries it forward. That is not the work of a genius. It is the compounding gift of a species that finally learned to think together and write it all down. The power that made an egg from skin is the same power that has to make it safe. We should be careful with it. We should also, for a moment, be a little amazed at the animal that could do this at all.