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a decent introduction but with too many errors
on August 23, 2013
In this small book, John Quackenbush seeks to explain what the Human Genome Project (HGP) is and the implications of its findings to science and medicine. Quackenbush may have been a late-comer to biology (having received his undergraduate and graduate degrees in physics), but since the early 1990s, he has conducted research in genomics under the auspices of prominent scientific institutions, including the Dana Farber Cancer Institute. The book is aimed at a general audience, and framed in non-technical language that will be easily understood by most interested readers. Following a brief introduction, the book begins with an overview of cells, genes, and protein synthesis. Chapter 2 considers the various species for which partial or complete genetic maps now exist. Chapter 3 explores the Human Genome Project itself, and what it has and has not revealed. Chapter 4 considers causes and treatments of the broad family of cancerous diseases. Chapter 5 considers other diseases with genetic components (i.e., diabetes, cystic fibrosis, and Huntington's disease).
Chapter 6 explores fascinating issues of what can be inferred from genetics about human prehistory, including our spread out of Africa throughout the globe. Quackenbush takes pains to rebut the potential misconception that "mitochondrial Eve" and her male counterpart were the only members of their species alive at their time. Unfortunately, he endorses a more common misconception, by asserting that mitochondrial Eve and Y- chromosome Adam "were our most recent female and male common ancestors" (p. 150). The quote is incorrect. These two person were only (by definition) our most recent common ancestors by strictly matrilineal and patrilineal lines. As work by Joseph Chang and others has shown, all living humans share a set of common ancestors of only a few thousand years ago (notwithstanding the much greater age of our matrilineal and patrilineal ancestors). (A highly readable account of this issue can be found in Richard Dawkins' "The Devil's Disciple".) Although "The Human Genome" states that "no DNA evidence suggests that humans and Neandertals interbred" (p. 151), compelling evidence of such interbreeding was published 10 months before this book was published. The final chapter ("A Brave New Genomic World") considers the future, touching on issues of stem cells, cloning, gene therapy, and ethical concerns.
Despite its general utility, The Human Genome contains many factual and conceptual errors. For example, to account for inheritance of maternal DNA, the text explains that "Male sperm cells do not contain mitochondria" (p. 147). On the contrary, sperm cells are packed with mitochondria, which provide all the energy that powers sperm locomotion. (What the author probably meant to say is that sperm mitochondria do not contribute DNA to the fertilized egg). As another example, the text states that "Mammals have been around for 510 million years" (p. 156). This is a mistake that an introductory student shouldn't have made. Mammals actually arose in the early Jurassic, about 190 million years ago. Perhaps the author was thinking of invertebrates, which date back over 500 million years.
To illustrate the pattern of Y chromosome inheritance, the text invokes the mutineers from the HMS Bounty who settled Pitcairn Island in 1790. We are told that the island was settled by 6 mutineers and 13 native women, and that 200 years later, only three of the original male surnames remain, due to "chance events that occur when men do not have sons" (p. 145). The example is misrepresented and misinterpreted. The early Pitcairn settlers actually included 15 men, 2/3 of whom were murdered in the first few years; only one was left by 1799. What's more, the original inhabitants of Pitcairn abandoned the island in the 1850s (see footnote *1). Descendants have come and gone since that time. Clearly present- day male surnames on the island do not simply reflect random patterns of mating.
The text attributes Charles Darwin's revelation about natural selection to his study of the Galapagos finches on the various islands (p. 24-25; p. 139). The account is misleading, since it was actually the island mockingbirds that led Darwin to question the stability of species. Further, Quackenbush credits Darwin with constructing a phylogenetic tree of the Galapagos finches (p. 139). On the contrary, no such phylogeny was constructed until the mid 20th century. In considering the genomics of evolution, Quackenbush mistakenly identifies "parsimony" as "the assumption that nature makes as few changes as possible as new species evolve from old ones" (p. 139). This an amateurish error that evidences significant conceptual confusion. Parsimony is a methodological principle, not an empirical statement about nature (much less, about evolution itself) (see footnote *2 below). In short, we do not assume that evolution is conservative -- rather, we adopt a method involving the fewest extra assumptions, as in all scientific enterprises. The difference is significant.
Such errors are troubling and would easily have been caught by a writer or reviewers with appropriate expertise. Given its errors, astute readers have good reason to wonder about the reliability of the overall work. Nevertheless, this book offers a reasonable account of the human genome and implications of the HGP in realms of science, medicine, and anthropology.
*1. The 1790 settlers of Pitcairn Island included 15 men (6 of whom were Polynesian), 12 women, and an infant. Through rivalries over women and ethnic conflict, 11 of the men (including all the Polynesians) had been murdered within four years (see T. Lummis' Life and Death in Eden). By five years later, only one man was left, and only some of the deceased men had left offspring. In 1856 the island was entirely abandoned. Only one family returned in 1859. Over the past 150 years, descendants of the original mutineers have come and gone from the island. Clearly the retention of male surnames among current residents of Pitcairn reflects historical events of multiple types.
*2. The principle of parsimony (sometimes known as Occam's Razor) is to make as few ad hoc assumptions as possible in making inferences and drawing conclusions. It is employed throughout the natural sciences and most human endeavors involving critical thinking. Whether a given pattern of evolutionary change has been conservative or not is an empirical question - and one that is only answerable through adoption of the methods of parsimonious analysis. In fact parsimony is what has allowed biologists to recognize innumerable cases where evolutionary change has been other than "conservative".