Y: THE DESCENT OF MEN
By Steve Jones
Houghton Mifflin, $25, 235 pp
THE X IN SEX: HOW THE X CHROMOSOME CONTROLS OUR LIVES
By David Bainbridge
Harvard University Press, $22.95, 192 pp
Reviewed by Mark Page
Above all, science is a good story. Explaining the world is fascinating business. Like any good story science is full of conflict and resolution, heroes and villains, twists of fate, and in this case, plenty of sex.
In Y: The Descent of Men, Steve Jones sets out to explain the history, and complications, of maleness. In The X in Sex: How the X Chromosome Controls our Lives, David Bainbridge attempts the same for the other half of this mysterious evolutionary dance.
To understand how a baby ends up male or female you only need to remember three things about the sex chromosomes: X, Y and Sry. The male's sperm determines sex. If a father's sperm delivers two X chromosomes (XX) to the mother's egg, it's a girl. If, on the other hand, he delivers one of each (XY), it's a boy. Contained on the Y chromosome, which is only carried by the male of the species, is the Sry gene, which is the genetic equivalent of a "boy switch." From there it gets a lot more complicated, according to Bainbridge and Jones, and things aren't always what they seem.
For instance, every woman "is a mixture of two different sets of cells, using different X chromosomes, as though she were two genetically different animals stirred together." Bainbridge explains this mystery, and its repercussions, in his chapter "The Dual Lives of Woman." Jones, in discussing maleness, points out that whether it is bright feathers, huge antlers or expensive sports cars, it is ultimately the female who chooses with whom she will mate. "Females go a long way to choose the sperm they prefer," he says. "Those who make sperm may be crafty, but those who receive it are cautious."
He also shows that there are thousands of ways of bringing genes together.
"A turkey makes a droplet of semen just visible to the eye, while Grevy's zebra delivers half a gallon. The fire ant pumps out enough cells on each attempt to allow his mate to produce 2-million young over seven years, while in a certain fruit fly size count, and the sperm - each as long as a finger - are rolled up and handed over one at a time. Hedge sparrows take a tenth of a second to copulate, but a shiny brown desert beetle found in Australia spends weeks at the business," says Jones. "Squid use a specialized arm as an explosive sperm-delivery system, and Japanese diners have hurt their mouths when they eat one cocked ready to fire."
Some animal species don't have an X and Y system at all: Their gender-determining genes are spread throughout many different chromosomes. The sex of some animals, particularly some reptiles, is determined by temperature.
While Jones focuses strictly on the Y, Bainbridge writes about both. In doing so he provides a more integrated view of the evolution of sex. "I hope to convince you that it (the X chromosome) is just about the most compelling little scrap of stuff in existence," he says, and proceeds to do just that. "The X is a bold, full size, bona fide chromosome, whereas the Y is a sad, shrunken, vestigial thing." Sorry guys. Both authors agree on the sorry state of the Y.
In explaining the evolution of the X/Y great divide, Bainbridge tells a fascinating historical tale of genes migrating from chromosome to chromosome, the way people change neighborhoods. The chromosomes, and the genes they carry, are not static devices but incredibly dynamic systems, with genes jumping from here to there, trading genetic secrets. Even the X and Y occasionally exchange information, but that is the exception. Normally the X and Y are like teenagers at their first dance. Girls on one side, boys on the other.
Next to telling a good story the most important characteristic of a science writer is his or her ability to put complicated scientific information in a form accessible to the lay person. Bainbridge deserves an award in that category. He renders understandable several of the mysteries of inherited diseases, like muscular dystrophy, hemophilia, even color-blindness, and explains how they are transmitted. In a delightful chapter called "The Duke of Kent's Testicle," he shows how X-inherited diseases have changed the course of history.
Readers will also appreciate his thorough indexing as well as a helpful glossary.
Bainbridge also provides short "interludes" between chapters. He uses these five or six page sections to explain concepts the reader needs to understand what comes next. Anyone who, in six pages, can explain how DNA actually works, has a real talent.
For "gee whiz" lovers Bainbridge lets us know that a single "rung" on the ladder of DNA is 332 trillionths of a meter. The X chromosome contains 160-million rungs making it about two inches long, but folded so elegantly it fits in the nucleus of a cell along with the Y and 22 other pairs of chromosomes.
Between these two English authors, Bainbridge is by far the better storyteller. Jones tries too hard to be witty in a dry, half-sarcastic, unmistakably English sort of way. He loves complicated historical anecdotes, humorous vignettes and going off on tangents. As a result his style is baroque with literary ornamentation, making the real story difficult to follow. He also has an argumentative streak, setting up straw men from among 19th century naturalists and knocking them down.
Bainbridge tells a very readable story about the mysteries of the X and Y chromosomes. For instance, if one in 12 men are normally color-blind, why is there an island in the South Pacific where everyone is color-blind? Hint: It has to do with the weather.
- Mark Page is a freelance science writer living in Ellenton.