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The Fly in the DNA

In San Francisco I once knew a woman who had been adopted as a baby. When first I met her she hadn’t seen her mother since the day she was born, and had never met her father or any other blood relative. When she was twenty-one years old, she managed, somehow, to track down her mother, who was then living in central California with a man, not her father, and four other children. My friend wrote to the family and was invited to visit them in their large, noisy house on the outskirts of a large town. On the day she arrived she stayed up talking late into the night. Finally everyone went to bed. But at around three in the morning my friend woke up. She often got hungry in the middle of the night, and was in the habit of making plain spaghetti at two or three in the morning. She decided to go down to the kitchen to see what was there. To her astonishment, she found her mother standing by the stove, boiling a pot of spaghetti. “That’s how I knew she was my mother,” my friend said. “She ate spaghetti in the middle of the night, just like me.”

Who are we, really? How much of what we do is a learned response to the assaults and rewards of life and how much is programmed in our genes from the moment of conception? This question is hardly new, nor are answers expected any time soon. One would expect recent advances in molecular biology to settle this issue once and for all, but they seem only to be adding to the confusion. In Time, Love, Memory, the science writer Jonathan Weiner takes us up and down the evolutionary ladder, looking for clues about the behavior of human beings from the DNA of insects and mice, and from the scientists who study them.

During the last forty-five years, a great number of discoveries about how cells work and how plants and animals develop have issued from molecular biology labs all over the world. In the 1950s and 1960s, many of the pioneers of the new biology were former physicists who realized that the kind of bold experimental and theoretical approaches that led to discoveries about the structure of the atom and quantum mechanics might also be applied to the study of life. In Time, Love, Memory, Weiner deals with the work of Seymour Benzer, who was in his twenties when he decided to leave physics and become a biologist. During World War II he worked in a top-secret government lab on semiconductors, and others would later build on his work to develop the transistor. Weiner suggests that, for the young Benzer, physics—or at least the physics in which he specialized—just seemed too easy. Benzer’s friends were eager to carry on their work in solid-state physics, or to set up lucrative electronics companies, but Benzer worried that the entire field was becoming pedestrian. On the other hand, in the late 1940s, biology posed truly mysterious questions about how living things are made.

Benzer took biology courses, apprenticed himself to several important biologists in the US and France, and soon made a name for himself in the painstaking field of gene mapping. Then, in the early 1960s, that old feeling came back. Gene mapping, it seemed, was becoming old hat too. By this time Benzer had had two children and had watched them, practically from the day they were born, behave like distinct individuals, as though some internal program were unfolding in their brains. At the time, the feeling was growing among molecular biologists that in their laboratories, all of life’s mysteries would eventually yield up their secrets. Mind, behavior, and personality were the deepest mysteries of all. What, Benzer and some of his colleagues wondered, might genes tell us about them?

Studies of geese, bees, cats, and other organisms seemed to suggest that animal behavior often follows inherited patterns. Without being taught, bees know how to pollinate flowers and cats know how to chase small, speedy objects. After spending a year doing little else but read about psychology, talk to his biologist friends, and think, Benzer decided to study the genes governing the behavior of the fruit fly Drosophila melanogaster.

The fruit fly is a winged insect about the size of Thomas Jefferson’s ponytail on the American nickel. It has big red eyes, a brown or black body, and six tiny wires for legs. It lives on moldy fruit and is thought to have evolved in Africa, where it cruises heaps of fruit and garbage around markets. Biologists have been studying fruit flies since the early part of this century, and these insects adapt well to laboratory conditions. They are born, reproduce, and die all in the space of a month or so, are not fussy about what they eat, and have a set of giant chromosomes that are easily visible under a cheap light microscope. By the time Benzer decided to become a fruit fly expert, scientists had already learned a great deal about genes and the development of embryos from studying them.

Fruit fly behavior is simple, and for Benzer this was a distinct advantage. If you wish to become an architect, you do not start by building Versailles. You would probably be better off starting with something small, like a shed. In the same way, if you want to study behavior, it is wise to start with something that doesn’t do very much.

Benzer began by making careful observations of fruit fly habits. First, he found that, like people, flies sleep at night. They also nap during the day, an instinct that may once have served to help them escape from the midday African sun, which can quickly dehydrate a tiny fly. Benzer hired an intelligent, meticulous postdoctoral worker named Ron Konopka, whose task was to find mutations in genes that affected a fruit fly’s sense of time. Eventually he found a strain of flies that overslept, didn’t take naps, and didn’t go to sleep on time with the other flies. Other researchers eventually showed that these flies had a mutation in a gene they called “period,” which encoded a molecule shaped, amazingly, like a little spring. It is not known whether this molecule works like a watch spring, but genes that resemble “period” are found throughout the animal kingdom, even in people, and it is possible that these genes have something to do with sleeping cycles in all animals.

Another of Benzer’s postdocs, named Jeff Hall, decided to study the sexual life of fruit flies. When fruit flies mate, an adult male approaches a virgin female and does a little dance with its wings, either in front of her or be-hind her, and then mounts her from behind. The pair spends a few minutes in sexual congress before detaching from each other. Within a few days, the female starts laying hundreds of eggs.

It was the dance that Benzer and Hall were interested in. Many insects dance, perhaps most famously the bee, which wiggles in front of its hive to tell its colleagues where the nectar is. Biologists had long suspected that the dances of insects were somehow hardwired in their brains. Hall studied a strain of flies in which the males shunned female flies and danced with other males instead. What’s more, these mutant males often formed long chains, with one fly hooked up to the posterior of another, and danced soul-train fashion all around the glass bottles they lived in. This behavior, like the deranged sleeping patterns of “period” flies, was also caused by a single mutation, this time in a gene they named “fruitless.”

A third postdoc in Benzer’s lab, named Chip Quinn, studied the intelligence of flies. Flies can learn simple things, especially about danger. If you put a fly on a piece of metal connected to a battery and throw the switch, it will fly away. Quinn put flies in tubes with metal platforms, blew in different odors, and gave the flies electric shocks. Eventually, after several such lessons, the flies got to know that certain odors meant trouble and avoided them. This ability seemed to be governed by a small number of genes. If one of these genes were damaged, the resulting fly could never learn about odors and electric shocks, even after many lessons. Another scientist later constructed an improved fly by engineering it to express an extra copy of the gene that encodes a molecule called “cyclic AMP- responsive element-binding protein,” which interacts with some of the fruit fly intelligence genes. This fly learned to avoid odors after only one lesson, and never seemed to forget it.

Weiner says this is equivalent to a forty-year-old man remembering a telephone number he had been told only once as a twelve-year-old child. In fact, this seems more like a forty-year-old remembering he got one hell of an electric shock when he was twelve; but even if Weiner overstates the achievement of the fly, the identification of this gene is no less an achievement for the scientists involved.

The story of the search for behavior genes in the fly is an impressive one and Weiner tells it well. He has a tendency, however, to be a bit grandiose. Throughout Time, Love, Memory, Weiner quotes portentously from Pascal, Dante, Proust, William Blake, various Greek philosophers, and other wise men, and seems to suggest that the eternal questions they posed are being somehow addressed by Benzer’s fruit fly experiments. The rhetoric is not altogether convincing. For example, in answer to Blake’s “Tell me what is a thought, & of what substance is it made?” Weiner writes sarcastically, “as if [Blake] were asking an unanswerable question.” Somehow, I don’t think Blake would have found “cyclic AMP-responsive element-binding protein” a satisfactory explanation of his inner life. Nor would Bishop Berkeley and Saint Augustine consider the problem of the meaning of time to be solved if someone had told them that a molecule called “period” regulates daily sleeping and waking cycles in an insect, or even in all animals. Without “period” we would still feel loss and despair, and still grow old and await death. We might have insomnia more often, but we would experience the tragic effects of time all the same.

Benzer’s experiments are brilliant in their own right, and Weiner’s attempt to connect them to the musings of philosophers can seem forced. But there is something even more worrying about Weiner’s book. For Weiner and for many of his biologist protagonists, the studies of fruit flies and their genes have implications for human behavior as well. Like Benzer’s extraordinary fruit flies, some people sometimes have insomnia, some men desire other men, and some people aren’t very bright. This has led many journalists and scientists to suppose that human beings, like fruit flies, are genetically programmed to behave in certain ways. The National Institutes of Health now provides about $30 million every year for research into genes alleged to affect personality. The search is now on for genes governing intelligence, depression, alcoholism, adventurousness, homosexuality, anxiety, and many other traits. How successful are these efforts likely to be? And what are the implications for humanity?

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