Humans share 99.9% of their DNA with one another. A remarkable figure that genomic science has clearly established.
You read that correctly: the 8.2 billion people on Earth share the same genome, differing by only 0.1%. A drop in the ocean. Yet one that changes everything.
Stay with us — we’ll explain.
99.9% of DNA in common
Pick any two people at random. Truly at random, from among the 8.2 billion human beings on Earth. Ask them for a small saliva sample. Extract their DNA. Process it through a high-throughput sequencer. Compare the results.
What is the result?
99.9% of their genome is identical.
To put it differently, 99.9% of your DNA is identical to that of the 8.2 billion other people living on this planet with you.
Your genetic differences—your genotype, the part that makes you biologically unique—are concentrated, on average, in only… 0.1% of your genome.
In practical terms, this represents approximately 3 million base differences in your DNA compared with other human beings.
Do 3 million sound like a lot? Not at all — it is a drop in the ocean. Why? Because the number of base pairs that make up the human genome—your genome and that of the 8.2 billion other people who share this planet with you—is not counted in millions.
It is counted in billions.
About three billion base pairs.
Give or take, of course — this is no time for nitpicking.
99,9 %. 0,1 %. Two figures worth thinking about, wouldn’t you say?
Scientifically. Philosophically. And above all, humanly.
Still there? Good.
99.9% Shared DNA…
And what about the remaining 0.1%?
For the more curious among you, let’s try to refine the picture a little and see what makes up that 0.1%—that drop in the ocean. Fair warning: you may need to brace yourselves, because some big words are coming…
For every individual—you, us, and the 8.2 billion other people who share this planet with us—there are, on average, around 4 to 5 million variants (differences) compared with a reference genome.
These are mainly SNPs (corresponding to approximately one different base every 1,300 nucleotides), but also so-called structural variants (InDels, duplications, inversions, and CNVs). It is this 0.1%—this drop in the ocean—that defines our genotype… and ultimately underlies our phenotype.
We told you so — we just couldn’t help using lots of big words…
Okay, time out, time out — let’s take a step back for a moment.
Base, nucleotide, SNP?!?
A few explanations…
A “base”? What is that?
It is one of the four chemical “letters” of DNA: A (adenine), T (thymine), C (cytosine), and G (guanine).
Et un nucléotide ?
Easy enough: a nucleotide is simply a base plus a sugar plus a phosphate group.
And so… what is a “base pair”?
In DNA’s famous double-helix structure, bases pair up in twos: A with T, and C with G. These are therefore called “base pairs.” As noted above, the human genome contains around 3 billion of them. The order of these base pairs is called the sequence. It is this sequence that constitutes the genetic information.
And SNPs, indels, and other CNVs? What are those?
They are “simply” changes of varying magnitude in the sequence.
- SNP (single nucleotide polymorphism): a point variation affecting a single nucleotide.
- InDels (insertions/deletions): a small number of nucleotides added or removed.
- CNV (copy number variation): large genomic segments that are duplicated or deleted.
All right… And what is a gene?
A gene is a segment of the genome, that is, a set of base pairs located at a specific position on a chromosome. It carries the genetic information required to produce a functional RNA molecule. This RNA carries a copy of the genetic information. It serves as its faithful messenger so that the cellular machinery can properly perform its protein-production function (yes, we really have just mentioned… messenger RNA).
And what about the genotype?
Ah! A genotype is the full set of genetic variants (differences) present in an individual’s DNA that make that individual unique. One may speak of the genotype of a specific gene or of the entire genome. As noted above, the genotype underlies the phenotype.
So, while we’re at it, what exactly is the “phenotype”?
Well, the phenotype is the full set of observable traits that make an individual unique (height, eye color, blood group, metabolism, sensitivity to drugs, and so on). It therefore results from our genotype—the combination of the genetic variants expressed within our now-famous 0.1%, our drop in the ocean. But it is also shaped by our “environment” in the broadest sense (diet, altitude, physical activity, exposures, climate, and so on), which influences gene expression (that is epigenetics—fascinating stuff, but we will come back to it another time).
And the reference? You mentioned one. Which reference are you referring to?
To properly interpret the results of an individual’s high-throughput DNA sequencing and detect potential variants—differences that may, for instance, account for a genetic disorder—the sequence data are compared with a reference genome. The latest major reference, published in 2023, is known as the human pangenome reference: a kind of genomic atlas constructed from the genomes of 47 individuals of diverse ancestries.
99.9% Shared DNA:
the number to remember
Didn’t catch everything? That’s perfectly normal.
Didn’t understand it all? That’s not a problem.
We promise we’ll take the time later to go over it again and clarify everything.
But for now, just remember these two numbers: 99.9% and 0.1%.
Human beings, wherever they are on the planet, share 99.9% of their DNA.
As for the 0.1% that makes us different:
They raise crucial questions: how can we better explore them? How can we better understand and study them? So that we can improve treatment, for example… And since they form the basis of each individual’s uniqueness, how can we preserve them? How can we protect them? How can we ensure that everyone retains full ownership of them?
As for the 99.9% of DNA we all share::
It seems to us that, through this figure, genomic science expresses a simple truth: beyond ethnic, physical, cultural, social, political, or religious differences, human beings are above all fundamentally alike.
In 2025, it may be time for this scientific truth to consign to the status of illusory archaisms the prejudices and ideologies that divide, kill, and oppress.
99,9 %. 99.9%. 0,1%. Two figures worth reflecting on.
Scientifically. Philosophically.. Two figures worth reflecting on.
Scientifically. Philosophically.
And above all, on a human level.
If you have stayed with us all the way to the end, thank you.
If you skipped a few sections because we went on a bit too long but still made it this far, thank you too.
See you again very soon.
L’équipe de GENARO
Selected Sources
- NHGRI (NIH) — Human Genomic Variation ; DNA Fact Sheet.
- Science (2022) — The complete sequence of a human genome (T2T-CHM13).
- Nature (2023) — A draft human pangenome reference.
- Collins FS. JAMA (2001). (JAMA Network, PubMed)
- NHGRI (NIH) — Glossaire & fiches : définitions SNP, CNV, variation génomique. (Institut Genomic)
- >1000 Genomes Project, Nature (2015) : référence mondiale de la diversité génétique (26 populations, 80 M de variants). (Nature, PubMed, Welcome to DTU Research Database)
- NCBI Bookshelf — Indel (définition). (NCBI)
- NCI (NIH) — Phénotype (définition). (Institut National du Cancer)
- ASHG — Prises de position (2018–2021) : une seule humanité ; dénonciation des mésusages de la génétique. (PMC, ASHG)
