Deep, thorough, and a bit overwhelming
One of the things that becomes clear in reading this fascinating book is that sequencing the human genome in 2001 was really just a small step toward understanding the human genome. Another bit of sobering clarity presented here (and perhaps of even more importance) concerns how we as a species are going to use that knowledge for good or ill as we genetically engineer (or not) the human genome.
The central theme of the book concerns two highly significant and somewhat amazing discoveries that are leading us to the modern understanding of how biological inheritance really works and how complex it is. The role of epigenetics (one of Dr. Ryan’s favorite subjects) and the significance of symbiosis in human heredity are highlighted and placed under careful scrutiny. Ryan in part sees epigenetics as “software” to the “hardware” of the genes.
And this brings me to a wider theme, that of living things working together symbiotically as they form an ever evolving ecology. When I first began to study evolution many years ago the idea of cooperation—symbiosis—among microbes, plants and animals was thought to be just a minor part of the overall picture of evolution. We now know that cooperation among species is much more important than a superficial notion of a “selfish gene.” Instead of calling the gene “selfish” better would be to recognize that the gene has a quality of enlightened self-interest and can turn its enemies into friends. Would that our phenotypes were always so clever!
Ryan defines “symbiosis” in the broadest sense of the term to include the early parasitic relationships that are unstable to relationships that neither harm nor help the partners to mutualism in which one or both partners benefit. Perhaps the most important example of mutualism is the relationship between plants and their fungal partners. Ryan calls this an “intimate symbiosis, with the plant supplying the fungus with carbohydrates for energy and the fungus supplying the plant with water and minerals.” (p. 148)
But before the central theme comes a little history. Ryan begins with Oswald T. Avery to whom the book is dedicated and others as he recalls their early work toward discovering the means through which biological characteristics are inherited. They discovered DNA. He follows this up with a very readable account of how James Watson, Francis Crick and Rosaline Franklin discovered the structure of the DNA molecule in 1953 (with a little (perhaps inadvertent) help from, among others, Linus Pauling!). Ryan makes the people come to life and provides some detail not given in Watson’s famous book The Double Helix.
Ryan then recounts the race to the actual sequencing of the human genome, a race that ended in something like a dead heat between entrepreneur J. Craig Venter’s Celera Genomics and the National Institutes of Health’s Human Genome Project led by James Watson.
The middle part of the book gets more technical as Ryan attempts a crash course in genetics for the layman along with an update on the latest findings and understandings. I found this part of the book challenging to say the least, and a bit amazing. The fact “that roughly 9 per cent of our human genome is now made up of retroviral DNA” (p. 162) gives one pause. As Ryan explains, an analysis of viral coding in our DNA allows us to look back in time and gain insights into “the great wilderness of the prehistory” while telling us about ancient invasions from viruses that infected our ancestors. The earliest known of these human endogenous retroviruses (HERVs) entered the human genome “somewhere around 30 million years ago.” (p. 222)
In some way our defense mechanisms were able to take in the viral code and turn it into something positive or at least neutralize it. And now like fossils in our genes the code remains, although in some cases it has been put to positive use. Strange. Ryan sees this as “powerful supportive evidence for virus-human symbiosis at genomic level.” (p. 169) It reminds me of the famous discovery by Lynn Margulis that the mitochondria that power our cells were once invaders that we somehow came to terms with by forming a mutually beneficial symbiosis.
Not so technical and very enlightening is Ryan’s concept of “genomic creativity.” He uses the acronym “MESH” for what he sees as the four distinct mechanisms of evolutionary change. They are “mutation, epigenetics, symbiosis and hybridisation.” (p. 145) Thus our idea of how evolution works has been greatly augmented since the time of Darwin or even from a couple of decades ago.
The next part of the book is about the prehistory and how we evolved from Homo erectus along with three other now extinct humans: Homo neanderthalensis, Homo floresiensis, and the most recently discovered “mysterious species,” Denisova hominins. I read with great interest about the latest discoveries via DNA analysis and other evidence (“archaeogenetic calculations”—see p. 219) on how the Neanderthal went extinct and especially what we now know about what the Neanderthal looked like (light skin, probably blond or reddish hair, blue or otherwise light-colored eyes), cogitated (brain bigger than ours with verbal modules), and lived (made thatched huts, made water craft, displayed symbolic ability etc.). Incidentally according to Ryan the Neanderthal is not extinct “but live[s] on as an integral part of our own hereditary pedigree.” (p. 272) In other words we mated with the Neanderthal and our greater numbers absorbed them, and now thirty or forty thousand years later their characteristics have been reduced to about four percent of our genome. In particular I am proud to know (thanks to 23 and Me) that my genome is 3.1% Neanderthal. That’s the 99th percentile!
This part of the book was of particular interest to me as Ryan goes back into the human prehistory and shows us what we have learned due to genetic analysis. The past is literally coded in our genes. Genomic analysis is shedding light on the discussion about how and when we came out of Africa. Also very interesting is the possibility of “a near-extinction event” that reduced the human “population to less than 10,000 individuals, and some think it may have been as few as 1,000.” (See pages 221-222.)
The final part of the book is about how our knowledge and understanding of our genome will change us, our societies and our evolutionary trajectory. Ryan touches on the controversies to come concerning genetic engineering of the human genome as he reveals that the first artificial genome (bacterial) has already been constructed, and that the first human embryo engineered. (See the final chapter, “The Fifth Element.”)
--Dennis Littrell, author of “The World Is Not as We Think It Is”