Most organisms earn a place on a lab bench because something about them is convenient. Yeast divides in a couple of hours. Mice come in inbred, genetically identical strains. Zebrafish embryos are transparent. Humans offer none of that. You cannot breed a defined human genetic cross, keep a colony in a facility, or dissect a developing human embryo on a schedule. For most of the history of biology, the human body was the subject medicine tried to understand indirectly, through animals, because studying it directly was either impossible or forbidden.
That changed over the course of the twentieth century, not through one discovery but through two, two decades apart, that between them turned human biology into something researchers could work with as directly and systematically as any model organism: an immortal human cell line grown in a laboratory dish, and a complete, shared reference sequence of the human genome itself. Together they made "human" not just the ultimate target of biomedical research, but one of its standard working materials.
Why human tissue resisted the lab bench
The obstacle was not squeamishness so much as biology. Cells taken from a person and placed in culture medium reliably stopped dividing after a limited number of generations and then died, a behaviour that would eventually be formally described in 1961 by Leonard Hayflick and Paul Moorhead, who showed that normal human fetal fibroblasts divide somewhere between 40 and 60 times before entering irreversible growth arrest. That finding overturned decades of belief, dating back to work by Alexis Carrel in the 1910s, that cells could in principle be kept dividing indefinitely outside the body.
George Gey, head of tissue culture research at Johns Hopkins Hospital, had spent years by 1951 trying to establish a continuously growing human cell line, without success. Samples would take root briefly and then, invariably, die out. It was against that backdrop of repeated failure that a sample changed the field.
An accidental immortal cell
On 8 February 1951, cells were taken from a cervical tumour biopsy belonging to Henrietta Lacks, a 31-year-old Black woman being treated at Johns Hopkins, without her knowledge or consent, a standard and legal practice for hospital tissue at the time. Gey's lab, working with his assistant Mary Kubicek, put the sample into culture using a roller-drum technique Gey had developed himself. Unlike every previous human sample, it did not stop dividing.
Gey named the line HeLa, from the first two letters of Henrietta Lacks's first and last names, and gave samples away freely to researchers who asked for them, which is part of why HeLa spread through laboratories worldwide so quickly. The cells proliferated roughly twenty times faster than Lacks's own normal cervical cells, and unlike normal human tissue they simply kept dividing as long as they had nutrients and space, a property later understood to come from the way the human papillomavirus DNA integrated into Lacks's tumour genome had disrupted a gene called TP53 and driven continuous activity of telomerase, the enzyme that rebuilds the chromosome ends that ordinarily shorten with each division and trigger senescence.
The practical consequences were immediate and large. HeLa cells were mass-produced to test the Salk polio vaccine, used in the research that established that humans have 46 chromosomes rather than the 48 previously assumed, sent up on early spaceflights to study the effects of zero gravity on human cells, and used in techniques that eventually contributed to in vitro fertilisation. For the first time, a laboratory anywhere in the world could order a flask of growing human cells the same way it might order a strain of bacteria, and run an experiment on human biology without a human subject in the room.
A hidden takeover
HeLa's success carried a cost that took fifteen years to surface. Because the cells grew so aggressively and were handled in the same laboratories, on the same equipment, as other cell lines, they had an unusual capacity to contaminate cultures that were never meant to contain them.
In 1966, the geneticist Stanley Gartler presented evidence, later published in Nature, that a set of supposedly distinct human cell lines held in laboratories around the world all carried the same rare glucose-6-phosphate dehydrogenase and phosphoglucomutase genetic markers, variants found almost exclusively in people of African descent. Since several of the contaminated lines were meant to have come from white donors, the only explanation was that they had all, at some point, been overrun by HeLa. Later work by Gartler and others confirmed that at least eighteen to twenty widely used "distinct" human cell lines were in fact HeLa in disguise.
The contamination crisis is, in a strange way, a measure of exactly how deeply human cell culture had already become embedded in ordinary lab practice by the mid-1960s. It also forced the field to take cell line authentication seriously, a discipline that still underpins routine short tandem repeat profiling of cell lines today, and it is a reminder that when a single human sample becomes a shared laboratory resource, mistakes and questions about identity travel a very long way.
Consent catches up with the cells
The ethical debt behind HeLa took even longer to be addressed. Henrietta Lacks died of her cancer in October 1951, months after her cells were taken, and neither she nor her family were told that a line derived from her tumour had been distributed to laboratories worldwide, until journalists and, later, Rebecca Skloot's 2010 book The Immortal Life of Henrietta Lacks brought the story to wide public attention.
The issue resurfaced concretely in 2013, when a German research group published the full genome sequence of a HeLa cell line to a public database without consulting the Lacks family, and a second sequencing project, from a team at the University of Washington, was about to be published in the same period. Because a person's genome sequence can reveal information about their descendants, the Lacks family raised objections, and the matter reached Francis Collins, then director of the US National Institutes of Health. Following meetings between Collins and the family between April and August 2013, the NIH announced a formal agreement establishing a six-person review panel, including two Lacks family representatives, to control access to HeLa whole genome sequence data through a managed database.
The takeaway: the same pattern shows up twice in this history. A sample or a sequence becomes valuable precisely because it is shared widely and used by many labs, and that same reach is what makes the ethics of consent and identity catch up with the science years, sometimes decades, later.
Building a reference sequence
HeLa turned human cells into a workable laboratory material. The second transformation turned the human genome itself into shared infrastructure, a literal reference other researchers could align their own data against, the same role a reference genome plays for any model organism.
The Human Genome Project was formally launched on 1 October 1990, coordinated by the US Department of Energy and the National Institutes of Health, initially under the leadership of James Watson and, from 1993, Francis Collins, with a planned budget of around three billion dollars over fifteen years. It grew into a public international consortium spanning centres in the United States, the United Kingdom, Japan, France, Germany and China, run in parallel with, and for several years in direct competition with, a privately funded effort at Celera Genomics led by Craig Venter.
On 26 June 2000, the public consortium and Celera jointly announced completion of a working draft covering around 90% of the human genome, at a White House event attended by President Bill Clinton and, by video link, UK Prime Minister Tony Blair.
"Today, we are learning the language in which God created life. With this profound new knowledge, humankind is on the verge of gaining immense, new power to heal."
The consortium's full analysis, "Initial sequencing and analysis of the human genome", was published in Nature in February 2001. The project was declared complete on 14 April 2003, two years ahead of its original schedule and coinciding with the fiftieth anniversary of Watson and Crick's DNA structure paper, at which point the sequence covered roughly 92% of the genome with fewer than 400 remaining gaps.
Whose genome is it, exactly
One detail rarely makes it into the headline version of this story: the reference sequence produced by the public consortium was not really a composite of many people in equal measure. Around 1997, Roswell Park Cancer Institute in Buffalo, New York, recruited volunteers by newspaper advertisement, and DNA from roughly twenty anonymous donors went into the sequencing libraries. But one of those donors, known internally only by a library code, ended up contributing a clear majority of the finished reference sequence, with the remainder assembled from the other volunteers, most of European ancestry. That single anonymous man's DNA still forms the backbone of large stretches of the human reference genome used today.
It is a fitting echo of the HeLa story: a resource built for, and shared by, the entire scientific community turns out on close inspection to trace back overwhelmingly to one specific, largely uncredited person.
Keeping the reference current
A finished genome sequence is not a static document. The Genome Reference Consortium, a small group of institutes including the Wellcome Trust Sanger Institute, the European Bioinformatics Institute, the US National Center for Biotechnology Information and the McDonnell Genome Institute at Washington University in St Louis, has maintained and progressively corrected the human assembly ever since, releasing GRCh37 in 2009 and its successor GRCh38 in December 2013, with further patches issued regularly since.
Even GRCh38 still had gaps, particularly around repetitive centromeric regions and the short arms of the acrocentric chromosomes, regions that were simply too repetitive for the sequencing technology of the early 2000s to resolve. The Telomere-to-Telomere (T2T) Consortium closed that gap using long-read sequencing technologies unavailable to the original project, publishing the first truly gapless human genome sequence, T2T-CHM13, in Science in April 2022: 3.055 billion base pairs with no unresolved bases across every chromosome but the Y, adding around 200 million base pairs of sequence that had never been assembled before, including entire centromeric arrays.
| Assembly | Released | Notable feature |
|---|---|---|
| Draft consortium sequence | 2000-2001 | First public draft, roughly 90% coverage |
| GRCh37 (hg19) | 2009 | Long-serving standard for a decade of sequencing studies |
| GRCh38 (hg38) | 2013 | Corrected errors, added alternate haplotype contigs |
| T2T-CHM13 | 2022 | First gapless assembly, centromeres and acrocentric arms resolved |
Alongside the assembly itself, NCBI's RefSeq project, introduced in 2000, has provided an independently curated, non-redundant layer of annotation on top of the raw sequence, tracking which stretches of DNA correspond to genes, transcripts and proteins, and it remains one of the standard sources researchers use to interpret what a given position in the genome actually does.
Human, the reference organism
None of this happened as a single planned programme. Gey was trying to solve a tissue culture problem, not build a universal reagent. Gartler was investigating an anomaly in cell line genetics, not designing quality standards. The Human Genome Project's planners argued for years about strategy and competed openly with a private rival. The T2T Consortium existed because sequencing technology had simply moved on far enough to finish a job the original project could not.
What connects them is the result. Human biology today is not only the ultimate justification for almost all biomedical research, it is also one of the field's working reference points: a genome assembly, continuously maintained, that other genomes get compared against, and a laboratory cell line, still one of the most widely used in the world more than seventy years after it was taken from a woman who never knew her cells would outlive her by generations. Humans became a model organism, in the specific technical sense of a shared, standardised, systematically studied resource, by exactly the same slow accumulation of tools, mistakes and corrections that built that status for every other species in the lab.