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Consider my consternation and sense of helplessness when I discovered that it was exceptional to find one among the late-term women visiting my clinic in possession of a normal hemoglobin count. More often, they ranged from mild (8-10) to severe (5-7) anemia. My mentors sadly shook their heads, explaining to me that fetal brains would most likely not develop properly if the mother was anemic; at worst the babies would suffer mental retardation, and at best they would fail to attain their full intellectual potential.

Outwardly, these very pregnant women seemed normal, but I soon learned to discern their anemia's telltale signs of apathy and lethargy. Paradoxically, they appeared well fed, and, even more puzzling, many were actually overweight. A peculiar side effect of iron deficiency is the dulling of the taste buds that sense sweets. To compensate, an iron-deficient woman craves carbohydrates.

I was often disconcerted to observe a pregnant woman bringing a carton of cornstarch into my examining cubicle, eating the white powder right out of the box during my interview so great was her drive to satisfy her carbohydrate hunger. Meanwhile, she was unaware that the real culprit was a lack of a vital mineral in her diet. Increased intake of calories contributed to her weight gain, giving her a deceptively healthy appearance; cornstarch, which in 1958 contained negligible amounts of iron, only contributed to masking the problem.

In the years that followed, I reflected many times on my frustrating experience in that metropolitan prenatal clinic. After I had immersed myself in evolutionary theory, I wondered why Mother Nature would favor the evolution of mothers whose internal circuit breakers did not protect them from endangering their babies and themselves. Humans, like all animals, have sensitive trip wires alerting us whenever salt, water, oxygen, or carbohydrate levels enter the red zone. Why were women in general and pregnant women in particular so blissfully unaware of their susceptibility to iron deficiency?

Human intelligence is measured, for want of a better standard, in IQ points. In the long march from anthropoid hominid toward Homo sapiens, the piling up of one IQ point upon another eventually propelled our species to the top of the IQ heap. Low maternal iron depots ultimately subtract IQ points from offspring, thus subverting the entire thrust of human evolution. Our species' females, it would appear, had traded away sufficient maternal hemoglobin levels, but for what? Where, I wondered, was the beneficial offset that could possibly justify such a Faustian bargain?

Curious about this matter, I sought the answer in my authoritative physiology textbook. The explanation proffered was that males led a more strenuous life than females and therefore needed a more robust aerobic circulatory system. Although initially I accepted this answer, as I grew older I increasingly suspected that it could not be the complete story. I doubted that any man engages in a more metabolically taxing activity than trying to form a seven-pound infant over a nine-month period from scratch. Also, the drain upon the energy stores of a breast-feeding mother are of the same order of magnitude as the demands made upon an Olympic shot-putter during his rigorous training.

A similar disparity appears in the CBC in some other animal species, such as chimpanzees and gorillas. Hematologists suspect that this differential has something to do with the red-cell-enhancing effect of testosterone and the red-cell-depressive effect of estrogen. (Men treated with estrogen for prostate cancer are at risk to develop anemia.) Compared with these other animals, however, the differences between a man's and a woman's CBC are deeper and wider. This variation gains in significance because the other species that manifest an inequality in the number of red cells between the sexes do not have a brain as large as humans do, and as we shall see, the human brain is very sensitive to any factor that diminishes its ability to gain access to oxygen. Also, anemia is quite rare among pregnant primates, yet it commonly occurs in the human line. Many years later, after learning more, reading more, and experiencing more, I began to harbor a growing suspicion that an important missing piece of the human evolutionary puzzle was hiding somewhere behind the innocuous-looking numbers I had noticed that morning so long ago on a routine CBC slip.

I confess that I had difficulty staying focused on this subject during medical school. An overwhelming avalanche of other facts, lessons, and procedures cascaded down upon me, and distracted me from pursuing the question. Besides, the subject of blood was not my passion in those days. As a teenager, I had stumbled onto Sigmund Freud's Civilization and Its Discontents, one of those seminal books that one discovers in youth that rock one's beliefs. My curiosity whetted, I made subsequent explorations deep into Freud's subterranean warren. I was so intrigued by what I was learning there, I became convinced very early on that my destiny was to become a psychoanalyst.

Looking back now, I think it would be difficult for someone who had not lived through the 1950s to appreciate just how profoundly Freud's ideas permeated the intellectual climate then. A rough indicator of his influence was that over 30 percent of my 1957 medical-school freshman class had initially aspired to be psychiatrists. (Many medical students switch from their original choice of specialty, as did a lot of my classmates.) I envisioned that I would become a dauntless spelunker of the mysteries of the mind. Psychoanalysis seemed to be the "open sesame" to the entrance of that dark cave.

As a young boy, I had loved to build model airplanes and play sports. I enjoyed drawing and fancied myself a budding artist. When I rotated on the surgery service, I discovered, to my delight, that this field of medicine provided an outlet for the skills I was incubating. Surgery seemed a perfect fit for me. It was romantic, challenging, and intensely exciting. The drama I witnessed daily, combined with my sensing the enormous gratification surgeons seemed to enjoy, changed my mind about a career choice. I decided to specialize in general and vascular surgery. Though I remained faithful to my aspiration to be an explorer, now I decided I would navigate the interior passageways of the body.

Maintaining adequate circulating levels of red cells in my patients became a central concern of mine. As a young surgical resident at Bellevue Hospital in New York, I experienced an exhilarating frenzy while running with a group of emergency-room nurses and doctors gripping a gurney carrying a gunshot victim. Our goal: Reach the operating room before the patient "bled out."

Throughout my career, I have, on occasions too numerous to count, glanced up from a particularly vexing operative field to monitor anxiously a forest of IV poles, their precious transfusions hanging like ripe fruit. I have had many years during which to contemplate the nature, importance, and vitality of this substance we call blood.

© 2004 Penguin, a division of Penguin Putnam, used by permission.

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About the Author

Leonard Shlain is the author of Art & Physics: Parallel Visions in Space, Time & Light, and The Alphabet Versus the Goddess: The Conflict Between Word and Image. He is the chief of laparoscopic surgery at California Medical Center in San Francisco.