Do Fathers Matter?: What Science Is Telling Us About the Parent We've Overlooked (4 page)

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The Aka give us insight into fatherhood from the time of our prehistoric ancestors, but they don’t tell us much about how fatherhood might have changed during the past few decades. As I said at the beginning of this chapter, men are shaped to become fathers not only by evolution but also by their own families and their environments. We are now learning that a family’s ill health and exposure to toxins in the environment can adversely affect their future children and even grandchildren.

Most of us know that a woman who becomes pregnant should stick to healthy foods, skip mercury-laden fish, quit smoking, and avoid exposure to paint thinners. All of these things, and more, can affect the health of the fetus. That’s easy enough to understand; we’re never more intimately connected to our environment than when we are in our mother’s womb.

The same sort of reasoning suggests that a father would have little or no impact on the health of the fetus, with which he has no physical connection whatsoever. But that reasoning is faulty: research is showing that a father’s environment, his behavior, and even his appearance can have a substantial effect on fetal health—and on the health of his grandchildren.

The first glimmer of this phenomenon came up in the mid-1960s. A pharmacologist named Gladys Friedler was studying the effects of morphine on female rats, and she found that the drug altered the development of their offspring. She then tried injecting males with morphine and mating them with healthy females to see if that exposure would also affect the offspring. The conventional wisdom was that it couldn’t; that the morphine might affect the males in a variety of ways, but that it wouldn’t affect their sperm. But the conventional wisdom was wrong. The rats’ pups were underweight and underdeveloped—solely from the fathers’ exposure to morphine before conception. Friedler didn’t fully understand what she was witnessing. Neither did anyone else; and nobody believed her. She struggled to get funding for more experiments, and colleagues urged her to abandon the research. But she persisted, and it is only within the past decade that her work has been confirmed.

Researchers have now seen signs of this kind of paternal inheritance in a number of recent studies. Some of the most interesting findings come from what is now an isolated resort community in northern Sweden called Överkalix parish, with mountains lit by the midnight sun in summer and the northern lights in winter.

Swedish researchers were drawn to Överkalix because careful historical records had been kept by town officials during the nineteenth century, when Överkalix was subject to repeated crop failures. Harvest statistics were collected in “Communications from the County Governor in Västerbotten to His Majesty the King,” and grain prices were recorded as well. Researchers had information on children born in Överkalix in 1905, as well as data on bountiful harvests and starvation back to the time of the children’s grandparents. The idea was to look for any connection between the grandparents’ diets and the outcomes of their grandchildren. During bountiful years, the grandparents would have had plenty to eat, and during lean years they would not have had nearly enough. The scientists didn’t know what they would find, but the data gave them the opportunity to see whether changes in men’s nutrition could have any health consequences for their grandchildren.

They looked at records that would tell them about the diets of grandfathers during their early adolescent years, a period thought to be particularly important for future health. And they found that diet at that stage of life had important consequences. The grandchildren of men who had plenty to eat did not live as long as those whose grandfathers had gone hungry. The grandfathers’ hunger was good for grandchildren in other ways, too. The grandchildren of these men were less likely to die of heart disease or diabetes than those whose grandfathers had had plenty to eat as adolescents.

Marcus Pembrey of University College London has reviewed the Överkalix findings and other sources of information to see what else he could learn about men’s behavior and diet and their effects on their children and grandchildren. He looked at data on 166 British fathers who said they’d started smoking before the age of eleven and compared their children to those of fathers who started smoking later in life. The sons of the fathers who started smoking early were more likely to be overweight by age nine. There seemed to be a link between fathers and their sons but not between fathers and their daughters.

Pembrey and his colleagues also looked again at the historical records of harvests in Överkalix to determine which grandparents had good access to nutrition in early adolescence and which did not. They confirmed the increased mortality risk in the grandsons of paternal grandfathers who had good access to food. And they found the same thing in granddaughters whose paternal grandmothers had plenty to eat. The opposite case was also true: grandchildren had lower mortality risk if their paternal grandparents had poor access to food as children.

There’s more. We have known that mothers who overeat or are obese during pregnancy increase the chances that their children will be obese. And now we know that a similar thing happens with fathers. The children of obese mothers
and
fathers are more likely to be obese themselves. This result comes from Margaret J. Morris and her colleagues at the University of New South Wales in Australia. They noticed that overweight children usually had overweight mothers and fathers, and they wondered whether fathers’ diets—not just their genes—would affect their children’s risk of developing type 2 diabetes.

The researchers fed male rats of normal weight a diet of more than 40 percent fat, which made them obese. Then they mated them with females who had been fed a normal diet. The male pups showed increases in weight and body fat, and tests indicated they had an increased risk of diabetes. The daughters showed a different pattern. Their body fat and weight were normal when they were born, but in adulthood, they developed a diabetes-like condition marked by alterations in the way they handled glucose and insulin. When Morris and her team looked closely at the daughters’ genes, they found alterations in the workings of 642 genes related to islet cells—the cells that produce insulin. There was only one explanation for this link: the fathers’ high-fat diets had produced alterations in their sperm, which then led to the occurrence of adult-onset disease in their daughters.

These alterations are referred to as epigenetic changes. They do not change the DNA sequence of genes, but they affect whether or not certain genes are expressed—meaning whether they are turned on or off. The findings of the Överkalix and obesity studies reflect such epigenetic changes.

Other studies have shown a similar connection in other ailments. A group at the University of Massachusetts led by Oliver J. Rando found that feeding male mice a diet low in protein substantially altered many genes involved in the metabolism of cholesterol and fats in their offspring. The group offered some interesting speculation about why this might be the case. Perhaps the father’s body, detecting that it is in an environment in which protein is in short supply, is altering the genes it passes on to its children to help them adapt to scarcity. “Mechanisms exist that could allow organisms to ‘inform’ their progeny about prevailing environmental conditions,” the researchers wrote. That is a remarkable and unexpected way for a father to help ensure the survival of his offspring.

Each of these findings led to more research, and the evidence that poor health in fathers can adversely affect their children is mounting. In a more recent finding, Eric J. Nestler of the Mount Sinai School of Medicine in New York and his colleagues exposed adult male mice to chronic stress, and then bred them with normal females. The pups showed physiological and behavioral changes resembling those of depression and anxiety. Lorena Saavedra-Rodríguez and Larry A. Feig at Tufts University School of Medicine in Boston found that female mice passed the effects of stress on to their offspring, but fathers passed those effects on to their offspring and to the next generation as well—another example of the grandfather effect found in the Överkalix studies.

Studies such as these are appearing all the time. The more that researchers look for these changes, the more they find them. In a study presented at the annual meeting of the Society for Neuroscience in November 2013 and later published in
Nature
, Brian G. Dias and Kerry J. Ressler of Emory University in Atlanta reported that the fear produced by traumatic experiences can be passed on from males to their offspring. They gave male mice small shocks when the mice were exposed to a certain odor, until the mice would show a startle response when exposed to that particular odor, not to others. When the mice were mated, Dias and Ressler found that the offspring showed an increased startle response to the same odor. And this fear was passed on to the next generation, too.

It’s important to remember that until the past decade, researchers did not anticipate finding anything like these epigenetic changes in fathers. It’s not surprising that the health of mothers would affect their unborn children; a mother and her fetus have a very intimate connection. But the only connection between fathers and the fetus is the single sperm that fertilizes the egg. It carries within a rich, and sometimes harmful, legacy. The question that remains is how these experiences of the fathers manage to change the epigenetic marks on their sperm so that the health risks or fears of the fathers are passed on to their offspring. Researchers have only hypotheses; nobody knows for sure.

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Other researchers have looked at the threats to fathers from toxins and pollution, to see whether exposure to these substances can produce changes in their offspring. Can toxins alter the operation of fathers’ genes the way stress, diet, and anxiety can? The first studies to address this question were done by Michael K. Skinner, a biochemist at Washington State University. He began by exposing lab rats to a fungicide called vinclozolin, used in vineyards and on fruits and vegetables. He wouldn’t have been surprised to find that exposure to the chemical harmed the rats. But he found much more than that. The fungicide switched on genes in the rats that normally were switched off, and vice versa—and these changes in the operation of the genes were passed on to their offspring. Researchers have known for a long time that chemicals in the environment can alter the operation of genes. But they thought that the genes in sperm and eggs were scrubbed clean of these changes before being passed along at conception. Skinner found that this was not the case. It was quite the opposite—the alterations had become permanent. The flipped switches were passed on to the next generation.

If exposures to the environment could alter the workings of genes that were once thought to be protected from outside influences, then it made sense to see whether men’s exposures to potentially toxic substances at work could produce harmful alterations in the operation of their genes. Tania A. Desrosiers and colleagues at the University of North Carolina did an epidemiological study in which they looked at large populations of male workers to see whether some jobs were associated with health problems in the men’s children. The hypothesis proved to be correct. Certain occupations of fathers were associated with a greater risk of birth defects in their kids. The riskier occupations included petroleum or gas worker, chemical worker, printer, computer scientist, hairdresser, and motor vehicle operator. Certain jobs were associated with particular birth defects: cataracts and glaucoma were linked to photographers, while digestive abnormalities were linked to landscapers. Epidemiological studies such as this always require confirmation in the lab and clinic, so we can’t yet be sure that this finding is correct. But it’s an important warning sign.

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These studies represent one unexpected way that fathers and even grandfathers can affect the health of their descendants. But there are other ways to look for connections between fathers and children’s health. One way is to see whether any other paternal attributes contribute to health outcomes in children. Some researchers are trying to find out whether a man’s looks have any consequences for his children. And they are finding provocative answers in, of all animals, zebra finches.

These birds, native to Australia, are about four inches long. The males have orange cheeks, striped gray-and-white throats, and red beaks. They might seem an unlikely species in which to pursue questions concerning men’s attractiveness. How, for example, would an investigator distinguish a particularly handsome finch from his plainer counterparts? Yet finches have taught us something interesting about fatherhood: the handsomeness of a male makes a difference to his children.

I heard this story from James P. Curley of Columbia University, an authority on the genetics of fatherhood. He doesn’t work on finches. He works on mice, which are also quite useful in the study of male genetics. But when I went to see him, he told me about the finches and walked me down the hall from his lab to a small room where some of his colleagues kept a noisy population of chattering zebra finches. Genetic tests of these small birds have shown that males can make important contributions to their offspring through an indirect route: by altering mothers’ behavior. Male finches can help their offspring’s chances of survival by making females become more adept at caring for their young.

The scientists who work with the finches looked at the question of whether the attractiveness of a male affects a female’s parenting behavior. The experiment was prompted by the curious sexual preferences of female finches, which have demonstrated that they prefer males wearing a red leg ring over males without one. The females show little interest in males with green leg bands. This discovery saved the researchers from having to figure out which finches are the best-looking. It turns out to be a question of choosing the proper accessories.

It’s impossible to know for certain why the females prefer males adorned with red rings, but female zebra finches find males with big red cheek patches extremely attractive, Curley said, and the red rings could somehow be mimicking the cheek patches. Even without a firm explanation, this was a phenomenon the researchers could use to their advantage. They put red leg bands on half a group of male finches and green leg bands on the other half. Then they compared the offspring of the attractive males to those of the homely green-banded males.