In trying to categorise a new arrival in the film Mean Girls one character asks: “if you’re from Africa, how come you’re white?” The mean girl cannot have been paying attention in class, because, as Adam Rutherford reminds us so elegantly in his latest book, we are all African – originally. The only homo sapiens on the planet 100,000 years ago were in Africa.

The mean girl can be forgiven her ignorance, since the way many of us (lay people and professionals alike) have been taught about our origins is flawed. The neat family trees and branch lines charting the steady progress of evolution, and those ubiquitous illustrations of the ascent of humans, in which we evolve step by step from bent-over apes to straight-backed homo sapiens, are not just simplistic, they are a profound misshaping of the truth.

If you take the notion that you have two parents, that they each also had two parents, and work backwards to an ever expanding family tree, then by the time you reach the eighth century and Charlemagne you will have accounted for 137,438,953,472 individuals, more people than have ever existed in total on the planet. Family trees, it seems, collapse and fold in; they zigzag across generations to produce a bewilderingly entangled mesh.

In untangling this mesh, Rutherford aims at no less than a retelling of human history. Imagine if Edward Gibbon’s The Decline and Fall of the Roman Empire were updated with the addendum “as told by genes” and you’d get a sense of the scale of the ambition. But then a writer who suggests his book is a continuation of Steve Jones’s masterpiece The Language of Genes is clearly not short of confidence.

Rutherford’s follow-up to his highly regarded first book Creation is an effervescent work, brimming with tales and confounding ideas carried in the “epic poem in our cells”. The myriad storylines will leave you swooning. A random sample includes: why the distribution of wet and dry ear wax in humans suggests that the people of South Korea might be the least smelly on earth; why the idea of a Danish Viking conquest of the British Isles involving rape and pillage is not borne out by a genetic legacy; and why monoamine oxidase A, the so-called “warrior gene”, ought not to be a valid defence in criminal trials.

In the first half of the book, Rutherford charts how we came to be. The “Out of Africa” argument is alive and well, but it’s complicated. “The dates and overall flow has profoundly changed with evidence provided by ancient DNA.” In their great migrations homo sapiens were both “mobile and horny”. A toe bone of a female Neanderthal who died 50,000 years ago in the Siberian Altai mountains exposes ancient humans’ inclination to mate with other species. Denisovans from the nearby Denisova caves also contributed to the modern human gene pool.

The second half explores the trickier question of who we are now, and the profound consequences of the extraordinary Human Genome Project (HGP) – the sequencing of the 20,000 genes, spread across 23 pairs of chromosomes comprised of 3bn letters of genetic code that contain the instructions that make us human.

Computer-generated model of a DNA molecule. Photograph: Getty Images/Collection Mix: Subjects

Rutherford, a trained geneticist, is an enthusiastic guide. He is especially illuminating on the nebulous concept of race, how it both does and doesn’t exist. In 1972 an academic paper asserted that there was more genetic difference within so-called races than there was between them. A black Jamaican can be more closely linked genetically to a white Englishman than to a black Nigerian. It all depends what you select for. In trying to group people, if for instance you select for adaptation to altitude, then genetically you’ll find a connection between Nepalese and Ethiopians.

Science, Rutherford reminds us, is a work in progress. Pillars of certainty from my 1980s medical school textbooks come crashing down as he uncouples diseases from groups of people with whom they were previously associated. In “genome-wide association studies” researchers take a sample of people with a particular condition and look for variants in changes to DNA that are not found in people who don’t have the condition. Tay-Sachs disease, long regarded as a “Jewish condition”, isn’t any more. As Rutherford points out, with “careful genetic counselling” it has all but vanished among Ashkenazi Jewish populations. DNA analysis shows how sickle cell trait (resulting from one copy of a mutated gene haemoglobin-B distorting the red blood cell to a sickle shape), once identified with sub-Saharan Africans and their more immediate new world descendants, is actually also found in the Middle East, the Philippines and southern Europe.

That example allows Rutherford to demonstrate how evolution can give with one hand and take away with the other. Sickle cell trait evolved to give protection against malaria (specifically from the parasites Plasmodium falciparum and Plasmodium vivax) whereas the full-blown sickle cell disease (with two copies of the gene) is a serious, sometimes life-threatening condition.

The pursuit of genetic science has often been a noble and selfless adventure. But skirting around the margins of this book is an intriguing and underexplored question: if the science of genetics strives for perfection, does it matter that its practitioners are flawed? Francis Galton was the founder of eugenics. Does the fact that he was also a gentleman scientist with innovative taxonomical ideas make his assertions about race any less odious? While Rutherford is no apologist for Galton, he goes some way towards rescuing him from his racism by acknowledging his pioneering research into identical twins, which led to the question that still haunts us today about the relative importance of society and inheritance in shaping human development (the phrase “nature v nurture” was coined by Galton).

Rutherford argues that rather than halting the advance of gene science, we all need to have our genomes sequenced

Galton’s keen commercial instincts about human self-curiosity were evident at the International Health Exhibition in 1884 when he set up an anthropomorphic laboratory. For threepence, punters were tested with biometric tools including devices to measure the head and nose, to be presented with a record of their chief physical characteristics. Rutherford sees modern equivalents in the DNA companies who exploit our thirst for definitive statements of our past and likely futures. Too often, he suggests, DNA ancestry tests should come with the warning caveat: the science of genetics is probabilistic. Rutherford politely skewers the fantastical reports made by companies who claim with GPS accuracy to be able to locate the village in which your ancestors lived.

The Human Genome Project, with endorsements from figures such as the former US president Bill Clinton, who believed we were “learning the language in which God created life”, has fuelled limitless public expectations. In the years since its publication in 2001 there has been an escalation in the level of carping over its supposed underachievement. Rutherford acknowledges that the HGP has yet to yield a cure for a disease or its eradication. But in his reading, genetic science appears under siege from a ragtag cabal of journalists (cynical and gullible), heretical populist doctors, and new age gurus and their vociferous followers, who question the value and expense of the research. Riding to the defence of his colleagues in science, Rutherford argues with admirable and passionate intensity that rather than halting the advance of gene science, we all need to have our genomes sequenced.

Above the swing doors of the dissection room of my 1980s medical school some wag once scrawled “Behold Man!” The dissection of cadavers with scissors and scalpels was a “necessary inhumanity”; the tracing of nerves, muscles and collapsed blood vessels did not just offer up the secrets of anatomy but opened a window into what it is to be human. The HGP with its much greater powers of resolution not only affords us a chance to behold man at a molecular level but provides a vision of a past that needs necessarily to be rewritten. Rutherford has proved himself a commendable historian – one who is determined to illuminate the commonality of Homo sapiens. So much so that by the end of A Brief History I was reminded of the aptness of the Jamaican motto: “Out of Many, One People”. Ultimately all a-we is one.

• Colin Grant’s books include I & I: The Natural Mystics: Marley, Tosh and Wailer (Vintage). To order A Brief History of Everyone Who Ever Lived for £16 (Weidenfeld & Nicolson, RRP £20) go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.