| ADAM'S CURSE: A Future Without Men Bryan Sykes New York: W. W. Norton & Company, 2004 |
Rating: 4.5 High |
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| ISBN 0-393-05896-4 | 318pp. | HC | $25.95 | |
From a scientist at the frontiers of genetic research comes a second book with some startling revelations. Bryan Sykes is a professor of genetics at Oxford University's Institute of Molecular Medicine. He is also one of the best explicators of that complicated subject. His first book, The Seven Daughters of Eve, introduced the world to the concept of mitochondrial DNA (or mDNA) and showed that all humans descended from one of seven maternal ancestors. Now, in Adam's Curse, he turns his attention to the male of the species. In its pages he discloses facts even more amazing — and somewhat disconcerting.
The book starts off slowly. Dr. Sykes spends the first three chapters describing how he delved into his own ancestry, uncovering after much legwork a thirteenth-century Sykes who dwelt beside a stream near Flockton, an ancient hamlet on the Yorkshire moors. That space could have been devoted to the main topics of the book, which are the fragility of chromosome structures and the purported advantage to a species of shuffling its genetic combinations rapidly, via sexual reproduction, versus waiting out the slow spread of mutations that arise in parthenogenesis. Sykes makes the argument over and over again that the advantages of sexual reproduction are illusory — only to reverse himself and point out why it is superior after all in the evolutionary sense. In fairness, the question is a vexing one, for which there was not a glimmer of an answer until the 1970s. The answer is, of course, that if your offsprings' genetic blueprints differ from yours, it becomes that much harder for a parasitic species — evolved to attack you — to strike them down as well.1
But species that take advantage of sexual reproduction can do so merely by swapping genes. So then, a secondary question arises: Why do sexually-reproducing species commonly manifest two somatic types, marked by differing secondary sexual characteristics? Why, specifically, are there women and men?2 The answer to THIS quandary is a condition which flows from the fact that eukaryotic cells, along with the nuclear chromosomes, have organelles with their own DNA.3 Sykes paints a picture of a battle royal that takes place when two such cells join to exchange nuclear genetic material: the DNA in the organelles, being incompatible with its opposite number, triggers a war of attrition which devastates both cells. As a result, he says, the cells have evolved "superior" and "inferior" classes (my terms). The superior type has more organelles, and thus is guaranteed to survive any mitochondrial holocaust. Furthermore, cells are marked as to class by proteins in the cell walls. The markers make sure that like cells never merge. This, he suggests, is the origin of the proverbial "war between the sexes". He describes the situation vividly on page 116:
Now let us see just how the similarities play out. Just like Chlamydomonas, when our genes are preparing for sex, as eggs or sperm, they are inside two mutually incompatible types of cell. Egg does not fuse with egg, nor sperm with sperm. But the nuclear genes of our distant ancestors have taken the Chlamydomonas strategy a lot further. They have avoided the damage caused by the deadly cytoplasmic wars by entirely stripping the cells of one sex of its cytoplasm. We see here the logical conclusion of the strategy Chlamydomonas uses to fix the outcome of the cytoplasmic wars before they begin. What better way to avoid the conflict altogether than by denuding the single-cell stage, the gamete, of one sex of cytoplasm altogether? And this is exactly what has happened. The gametes of males, the equivalent of the handicapped minus-cell losers in the Chlamydomonas wars, have been systematically stripped of their cytoplasm until they are whittled down to a nucleus and very little else. These cells have become the sperm in animals and the pollen in plants. The single-cell stage of the female, on the other hand, has become the egg: a large cell absolutely bursting with cytoplasm and packed with literally thousands of mitochondria. |
Dr. Sykes soon gets to the main points of his narrative: the Y-chromosome of the human male and how it differs from the matrilineal DNA carried in the mitochondria. Here the seeming irrelevancy of the quest for the Sykes patrimony vanishes when, beginning in Chapter 14, the author ties it to his painstaking research into the proliferation of other Y-chromosome patterns. In the south Pacific, samples from Raratonga show that Thor Heyerdal was wrong: Polynesia was not settled from South America, but from Asia. The distribution of two other patterns, those of Somerled in Scotland and of Genghis Khan across Eurasia, are even more relevant to the historical record. Exploiting the advantages of great wealth and power, the two rulers created conditions that assured their genes far more than proportional survival in the general populations where they occurred; they dominated.4 However, the ancestor of the Sykes clan had no such wealth or power. Did the success of his pattern, then, the author asks, flow from some inherent advantage? Was the Y-chromosome somehow causing more children to be born male?
That question hangs in the air as the reader enters Chapter 21, The Rise of the Tyrant. The reader will find no answer to it here. Dr. Sykes has already shown us that he is a competent scientist and an indefatigible researcher. He has demonstrated the ability to write clearly and accurately and, when he describes his beloved Scotland, quite as evocatively as any travel writer. But he has also shown a tendency to personalize inanimate objects and forces, and to describe them in overly florid language. In this chapter — evidently driven by concern for modern man's environmental depredations — he gives full rein to both tendencies. The result is a markedly polemical chapter — as witness these excerpts from pages 234-5:
The invention and adoption of agriculture was accompanied by new concepts with a far greater lasting consequence, concepts which were unknown before the first seed was planted or the first animal tethered to a tree. These concepts were property, wealth and power. They were entirely new and played straight into the hands of our old friend — the Y-chromosome — as a new and irresistible instrument for sexual selection. Now, at long last, there was an opportunity for Y-chromosomes that could get hold of these valuable assets to increase almost without limit; an opportunity to pursue their instinct for endless replication that had until then been contained. It was, in my view, men and through them the Y-chromosome that seized on this trio of property, wealth and power and pushed them to their present absolute prominence. It may even be that this seductive combination, coupled to the unstoppable force of sexual selection, was not the passive and innocent product of agriculture and husbandry but the driving force behind its spread around the world. With property, wealth and power to play with, the Y-chromosome suddenly found a way not only of beating its rivals, other Y-chromosomes, but of crushing an age-old enemy — the mitochondria, guardians of the feminine. Innocent agriculture was the key that unlocked the chains that had restrained the raging beast of Adam's Curse and let it loose upon the world. |
| * * * |
The greatest casualty of all is the fission of the sexes. The blind rage of the male, released from its chains, has slowly and deliberately enslaved the female. |
Sykes goes on in this vein for several more pages, pointing out that once men had given up their hunter-gatherer ways and settled down in cities, they could afford to impregnate women more frequently since there was no need for children to keep up with the fast-moving nomadic tribe. The women were kept pregnant, and thus dependent on men, much of the time. Their children were weaned much sooner, a practice we still follow and which, according to Sykes, causes damage to their immature psyches even today. Ultimately, he claims on pages 240-241 that we are on the express train5 to disaster.
The limits to sexual selection imposed on the animal examples we looked at in an earlier chapter are reached only when the adornment is so disadvantageous that it becomes a burden — the huge male elephant seal that is so heavy it cannot get onto the breeding beach, or the peacock whose tail is so splendid and so large that it cannot fly away from predators. But there is no natural limit to human sexual selection based on wealth and power. There is no negative feedback control. Wealthy and powerful men are not disadvantaged. They generally get richer still. The mad scramble, fuelled by the most basic of unseen genetic impulses, seriously endangers the survival of the species — and the planet. In ten thousand years we have changed from an intelligent and resourceful animal, quite rare but with remarkable skills and a natural part of Gaia's world, into a teeming species very rapidly destroying her beautiful planet. |
In fairness, I acknowledge that Chapter 21 describes the origins of agriculture and husbandry quite sensibly, and Dr. Sykes has certainly done his homework on the ancient cities of the Fertile Crescent6 where those arts arose at the dawn of human civilization. It is only the overly reproachful tone of the writing, and the fact that he fails to make his case for the Y chromosome's direct influence on the sex ratio of offspring, that weaken it.7
To hold interest, any tale must have drama as well as conflict — and drama requires an enemy who is capable of putting up a fight. Dr. Sykes gives us just this in Chapter 22 as he abandons diatribe and returns to his usual explication. There are, he reveals, examples of selective induced death of males in the womb, or more accurately in the egg, since these examples are found among insects. Trichogramma is the clearest. In a remarkable series of experiments, William Hamilton showed that the complete lack of males among adults of this tiny parasitic wasp was due to the influence of a bacterium that turned male embryos into females.
Tantalizing hints of similar effects have been uncovered among humans. Dr. Sykes makes much of what he calls "The Sperm of Tara";8 their mitochondria have been shown to supply less energy, so that they don't swim as fast. What puzzles me is how this effect is supposed to select for females at the expense of males. Consider: The male produces sperm that either carry the Y chromosome or they don't. In both cases, the sperm's Taran mitochondria will reduce its motility. Assuming it is still able to reach and penetrate the egg (and it must be, or there would be no trace of such mitochondria) the probabilities of male and female offspring are unchanged. No, if such an effect exists in humans, it must operate after conception, probably when the "SRY" gene kicks in to divert the development of the fetus down the male pathway. Am I missing something? (This may be the biological equivalent of Louis Frank's theory about a constant rain of water comets.)
Dr. Sykes next examines the evidence for the so-called "gay gene", finding it inconclusive, but speculating that if there were such a gene, it might be a mechanism by which mDNA selects against male children (if only in the following generation). This is another instance of "tantalizing hints". Finally, he foretells the impending doom of the Y chromosome. It seems that this chromosome, cut off from pairing during meiosis and thus unable to repair itself, is being whittled down to a useless nubbin by random mutations. Dr. Sykes estimates it will be gone in 125,000 years, a figure he admits is preliminary. He discusses possible means of averting its disappearance — and the consequent demise of humanity.
Dr. Sykes' prose is never dull, and occasionally it sings. It also conveys a lot of intricate information in a very clear and accessible manner. That information is, in my judgement, vital for everyone who is concerned about the future uses of biotechnology — and that means everyone. The book is well researched and competently indexed. It does have defects; I mention some of them above, others on the Errata page. Despite its shortcomings, I recommend it. But I have the feeling that starting with The Seven Daughters of Eve (which I haven't read) would be a good idea.
To contact Chris Winter, send email to this address.