My Royal Blood, Or, A Gene's Eye View of History

Book Review:

Adam Rutherford, "A Brief History of Everyone Who Ever Lived: The Stories in Our Genes", Weidenfeld & Nicolson, 2017.

In the epilogue to the latest edition of The Selfish Gene (see my review here), Richard Dawkins marvels at modern techniques in genomics, which can reveal the geographic and demographic traits of our ancestors. As an appropriate follow-up to that book, I decided to read Adam Rutherford's A Brief History of Everyone Who Ever Lived, which Mr. Dawkins himself apparently considers "stimulating" and "right". The title of the book seems to be inspired by A Short History of Nearly Everything, but that's just my hunch.

Needless to say, A Brief History of Everyone Who Ever Lived is not literally about everyone who every lived. Rather, it is about the history of the human species viewed through the lens of genetics (in combination with some archaeology, anthropology and so on). But in a sense it is about every person, for reasons that are explained in the book. Here is a quote from Chapter 3:

"... no matter the languages we speak or the colour of our skin, we share ancestors who planted rice on the banks of the Yangtze, who first domesticated horses on the steppes of the Ukraine, who hunted giant sloths in the forests of North and South America, and who laboured to build the Great Pyramid of Khufu." (p. 152)

That is Rutherford quoting from an academic paper by Yale statistician Joseph Chang (see here). It is a striking conclusion, because it suggests that you can't really brag about being descended from Cleopatra, the Vikings or Charlemagne -- we all are! From a genetic point of view it is somewhat trivial; but to understand why, you'll need to let me summarize the first two chapters of the book.

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The common image of Homo sapiens as the pinnacle of evolution is mistaken. According to Adam Rutherford, there is no objective measure of progress in evolution -- every species is equally unique in the sense that it is evolved for its unique circumstances. Moreover, we don't know how apes evolved into us, as the following graphic illustrates:

As you can see, it is not a clean branching tree but more like a rootless bush. We believe that there existed at least seven species of archaic human (Homo erectus, H. ergaster, H. heidelbergensis, H. antecessor, and H. floresiensis, H. neanderthalensis, and of course H. sapiens). Unfortunately, DNA is rather fragile over millennia and we have not yet recovered DNA except from Neanderthals and Denisovans (who do not yet have an official taxonomy classification).

Without going into too much detail, the way DNA works is that there are four nucleotide bases (A, T, C, and G) that are like the letters in the alphabet -- and these "letters" are strung together in sequences of "words" (genes) and "sentences" (chromosomes). We can even look at "syllables" (codons, which are arrangements of three bases that encode for a specific amino acid). The human genome has approximately three billion bases, organized into 23 pairs of chromosomes. Well, twenty-two of those are true pairs (called autosomes), and then there are the sex chromosomes, XX for women and XY for men. The Y chromosome is passed from father to son. But everyone also inherits a bit of mitochondrial DNA (which sits outside cell nuclei) from their mother. So, mtDNA and Y let us trace maternal and paternal lines of ancestry, respectively.

However, the classifications used by taxonomists do not actually depend on DNA; they primarily look at anatomy. Although the Neanderthals look physically different from us, analysis of Neanderthal DNA shows that Homo sapiens and Neanderthals almost certainly interbred. As Rutherford writes, humans are "horny and mobile" -- we migrated out of Africa at least 100,000 years ago and dispersed all over, having sex with the Neanderthals in Europe. If you are of European descent, you likely carry Neanderthal DNA. Meanwhile, Denisovan DNA has been found in modern Melanesian populations; apparently there was a lot of sex in our past! Thus, from a genetic perspective, it is not so easy to draw a clear line between separate species. Life changes continually.

Even after Neanderthals went extinct about 30,000 years ago, the humans in Europe continued to change physically and culturally. Especially in the last 10,000 years -- when we started domesticating animals and cultivating plants -- our bodies got more genes for producing amylase, an enzyme in saliva that helps digest complex starches. Europeans have also evolved to digest milk as adults thanks to the lactase enzyme, which is unusual in view of the fact that most adult humans throughout history have been lactose intolerant. These are examples of how farming, an aspect of culture, has impacted our DNA. But modern genetic studies can also tell us surprising things about what happened historically: for example, one project looked for clusters of genetically similar people across the British Isles, and found that Welsh Celts are more different to Scottish Celts than either are to the English. And despite a history of Danish Viking invasions of Britain, there is almost no Danish DNA in the British genome -- suggesting that these people did not integrate with the locals. On the other hand, the people of Iceland have Y chromosomes traceable to Scandinavia and mitochondrial DNA associated with Ireland and Scotland -- suggesting that Norwegian Viking men bred with Scottish and Irish women before settling in Iceland. Unfortunately, DNA from ancient Africans is less readily available due to heat and humidity.

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So far we have seen how our ancestors bred with Neanderthals, how farming culture altered our DNA, and how new models of gene flow are challenging our assumptions about movement patterns. As Rutherford puts it:

"... we made assumptions about patterns of migration that were much more linear and spread like ripples, rather than the picture that has emerged in the last couple of years, which says that we moved in all directions all the time, and laid our hats and flowed our genes in a matted crisscross, instead of a nice clean radiation." (p. 83)

In Chapter 3, the author discusses the last 1,000 years of European history: a time of kings and emperors. He opens the chapter by quipping how people find it prestigious to have their bloodlines traced to royalty like Charlemagne, the first Holy Roman Emperor. Yet everyone who is of broadly European descent can claim to be a descendant of Charlemagne! This is because:

"... pedigrees begin to fold in on themselves a few generations back, and become less arboreal, and more a mesh or web-like. You can be, and in fact are, descended from the same individual many times over." (pp. 146-147)

Mathematically, given the current population of Europe you can calculate that the most recent common ancestor (in terms of family trees) would have existed about 600 years ago. This happens to be around the time of King Richard II of England. In terms of DNA, commercial genetic ancestry kits like the one provided by 23andMe can tell you that you have a higher-than-average chance of developing Alzheimer's disease or that you are descended from Vikings, but this has little sway over your destiny -- such companies mainly sell us exciting yet often speculative stories, not scientifically meaningful insights. Rutherford compares it to astrology by way of the Forer effect (aka Barnum effect). Again, this is because "we all are a bit of everything, and we come from all over" (p. 165). No tribe is permanent.

More interesting than Richard II, perhaps, is Richard III. He died in battle in 1485 and was buried at the Greyfriars monastery in Leicester. In 2012, a team of diggers found his skeleton under a parking lot, and genetic testing confirmed Richard's identity. This was done by comparing the mtDNA extracted from the bones to the mtDNA of two living women who are maternally descended from Richard's sister, Anne of York. Of course, the skeleton itself also matched historical descriptions. Thus, Richard III is the oldest dead person clearly identified so far.

The rest of Chapter 3 contrasts the successful study of Richard III with the not-so-successful claim that Jack the Ripper has been identified. Rutherford goes on to discuss the phenomenon of inbreeding within the Hapsburg family, and how consanguinity (e.g. marrying one's cousin) has the silver lining of allowing geneticists to better understand the genetic components of various diseases.

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Thus concludes Part One of the book, which was about "how we came to be". Part Two is about "who we are now". In Chapter 4, Adam Rutherford tackles the thorny question of race -- and he makes it clear what his position is:

"... there are no essential genetic elements for any particular group of people who might be identified as a 'race'. As far as genetics is concerned, race does not exist." (p. 214)

Somewhat ironically, modern genetics is based on the statistics invented by proponents of eugenics such as Francis Galton, who tried to formalize the differences between people and rank them. But after the double helix of DNA was revealed in 1953, researchers began to understand that the greatest proportion of genetic differences exist within racial groups. The total amount of human variation is greater than skin-deep: two black people may be more different to each other than a white person and a black person. There are certainly differences; for example, South Koreans are much more likely to have dry earwax, and East Asians in general have an increased density of sweat glands. Yet the way we commonly talk about races (e.g. Caucasian, Asian, African, Native American, Aboriginal Australian) bears little resemblance to the science of genetics. Thanks to the Human Genome Project, we can see that human variation sits on a continuous spectrum -- you can point at geographical genetic clusters, but they are very rough, overlapping, and non-essential. Few of us would consider the Kalasha of northern Pakistan a separate racial group. Thus, as Rutherford argues, it is meaningless to ask how many races there are. Moreover, all humans alive today share a common origin about 3,400 years ago, so the notion that black people are closer to "primitive man" is just racism.

Speaking of the Human Genome Project, the next chapter discusses its background and impact. In 2003, scientists arrived at the number of genes in the human genome: about 20,000. However, that number does not include sections of DNA that do not code for proteins. Even so, we have surprisingly few protein-coding genes; roundworms and bananas have more! Another surprising finding is that most of the DNA we carry does not seem to do anything useful. (If you have read my summary of Bill Bryson's "A Short History of Nearly Everything", you probably already knew this.) The Human Genome Project took nearly a decade and $3 billion, and was described by then-president Bill Clinton as "the most wondrous map ever produced by humankind". Since the HGP paper was published in Nature in 2001, we've dramatically lowered the cost of gene sequencing and carried out a frenzy of research. A common technique is called a genome-wide association study, or GWAS. It looks for genetic differences in people who have a certain disease and people who don't, usually with very large sample sizes. Unfortunately, all this research has not yet helped us cure diseases. This is partly due to the complexity of biology -- diseases are often caused by the interaction of many genes (rather than one gene) plus the environment. Rutherford closes the chapter by calling on readers to join the movement to genetically sequence everyone.

Chapter 6 of A Brief History of Everyone Who Ever Lived looks at the question of fate: are some people genetically destined to be criminals? Courts have actually reduced the sentencing of defendants who have certain alleles of the MAOA gene (which has been associated with aggression and compulsive behavior). As it turns out, genetics and brain scans do not offer definitive proof that someone will behave in a certain way. The DNA and the brains of serial killers are human. Says Rutherford: "Inheritance is a game of probability, not of destiny" (p. 340).

In the final chapter, the author explores the future of our evolution. Indeed, we are still evolving -- for example, some women (about 1/8) have a fourth type of opsin (a protein that lets the cones in our eyes distinguish colors) coded by their X chromosome, giving them tetrachromatic vision. As discussed earlier, our farming has also changed us. Moving north changed the pigmentation of our skin. Sickle cells may be an adaptation to malaria, since it offers protection. And we will continue to evolve as long as we keep reproducing. Regarding the future, Rutherford is reluctant to make predictions, because a scientist must doubt everything they think they know. It is, however, unlikely that we will grow wings. (We already fly all the time.)

There is also an Epilogue, in which Rutherford reflects on the uniqueness of every species, and the uniqueness of every individual. We also share similarities, and our DNA was drawn from millions of past lives, who we shall bring with us for as long as humans endure.

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A Brief History of Everyone Who Ever Lived is a fascinating book, and will likely challenge your prior beliefs about genetics or answer questions you never knew you had. It tells us that we all share a surprisingly recent common ancestor; that our ancestors continually migrated in all directions; that we carry genetic traces of the Neanderthals and Denisovans; that every fossil is in a sense a transitional fossil; that looks can be deceiving when it comes to "race"; that there is no single gene for intelligence; that culture has altered our biology and that we continue to evolve; and that DNA is not destiny. Furthermore, these lessons also serve as illustrations of how science is not "finished" -- scientists are continuously refining their theories and slowly inching toward truth, especially when it concerns humans.

Adam Rutherford's writing is not bad either, but I have to nitpick about the organization of the text. It's sometimes hard to figure out what the author is getting at, or whether he's going off on a tangent or making a key point. At the end, there isn't a single clear conclusion (other than the tautological "we are different and also the same"), which makes the book feel slightly anticlimactic. I suppose a part of it might also have to do with the lack of "practical implications", other than being more skeptical of personal genetic testing companies. The interesting tidbits in the book will appeal mainly to readers who are curious about these things for the sake of it. I happen to be one of them, but I can see how this may not be a book for everyone. These are the main reasons I would rate it at 4 stars rather than 5. That being said, it's worth reading if you want to learn more about the evolving science of genetics.