Do Fathers Matter?: What Science Is Telling Us About the Parent We've Overlooked (12 page)

To learn about the California mouse at a study site near Monterey, California, he needed to set scores of traps in the field, capture the mice, tag them, and release them. “You set up a grid, where you have two live traps, metal rectangular shapes that have a folding door in front. And when the animal walks in to get food in the back, the door slams shut. You have lines of traps that maybe are ten yards apart or so.” Gubernick and his colleagues then crawled around on the ground, sometimes in the mud, opening these traps, making measurements, and releasing the mice.

In the winter, Gubernick would place a small wad of cotton bedding in the traps to help keep the animals warm. The scientists weren’t so lucky. “It can be miserable if it’s raining and cold,” he says. “You have a headlamp on, and a handheld ultraviolet light, and you’re marking these animals with little numbered ear tags to identify each individual.” And opening the trap can be a surprise. “Sometimes you get other mice in there, sometimes insects, and other animals who might try to put their nose in the trap and close it.” All the fieldwork is done at night, in the dark, because that’s when the animals are active.

Gubernick dusted females with different colors of pigmented powder, using pigments visible only in ultraviolet light. Matching the colors that rubbed off on the males with the females after they had mated in the wild showed who they nested with; later genetic testing demonstrated for the first time that they were strictly monogamous—the male paired with the female was the father of all her offspring. “It may be the only truly monogamous thing in California,” Gubernick cracked.

The fieldwork built on his earlier laboratory findings, in which he had bred the mice and removed the fathers from their mates and offspring. The idea was to see whether their absence would have adverse consequences for the pups. The results were a little more complicated—and more interesting—than you might think.

Gubernick set up three sets of conditions: a warm room with food and water; a warm room where parents were required to work for food (that is, they had to run on a wheel before food would be dispensed); and a cold room where they were likewise required to work for food—to mimic winter conditions. With food and a warm room, removing the father had no effect. Where fathers had to work for food or perform in a cold room, they clearly enhanced the pups’ survival. These circumstances, in which fathers were shown to make a difference, more closely resembled natural conditions.

Next, the researchers did the experiment in the field, with similar results. They removed the males from half of a selected group of nests, and left the males in the other half. Fewer young emerged from the nests in father-absent families than in father-present families—indicating that without a father’s care, more were dying. The reason for the increased survival in father-present nests was the direct parental care provided by the fathers. Male parental care presumably evolved because it was critical for survival of the offspring. Gubernick says his study was “the first demonstration in the wild that males were indeed necessary for offspring survival.” Additional data showed that the primary importance of fathers was not for protection but to provide direct care of their young.

Gubernick has also shown that males engage in as much parental activity as females, licking pups, carrying them, and huddling over them. Those activities keep the young warm—a critical factor in survival because the pups can’t regulate their own body temperatures until they are about two weeks old. And he also found that prolactin—the hormone associated with nursing—was elevated in fathers after the birth of their offspring. We’ve already seen that it rises in birds, other rodents, and humans. The prolactin levels of the male California mice were the same as those of mothers, suggesting that prolactin levels correlate with the fathers’ parental behavior.

*   *   *

The differences in the paternal behavior of California mice and deer mice were easy to see in Lambert’s laboratory. But identifying the differences in their brains that gave rise to their behavior would require months of experimentation. Lambert and her students set up their experiments so the mouse fathers—the good and the bad—were separated from other mice, including their pups, for twenty-four hours, and then exposed to their own pups, to somebody else’s pups—these were so-called foster dads—or to brothers they’d been raised with. This last group would serve as the control, because those males wouldn’t be exposed to any young mice at all.

The idea to separate the fathers and pups before the experiment came from Lambert’s reflections on her own parenting. “The more I thought about it, I realized that my circuits are most activated when I’ve been separated from my kids—and reunited. So we thought, we’re going to separate everybody for twenty-four hours from their brothers or their families. And then we’ll put them into the cage with their own pups or just their brothers, so we could see if the brain changes occur when they came across any familiar animal or just the pups.”

Once the team had done these experiments, they sacrificed the fathers and dissected their brains, making extremely thin slices and examining them to see which neurons were active. “It’s kind of like a PET scan,” Lambert explained. They also determined whether the fathers’ brains were restructuring or growing new neurons as the mice became fathers, or foster fathers in the case of those exposed to others’ pups.

They ran similar experiments with mothers, so had some sense of what they might see with fathers. “We had found that the moms had some plasticity—some changes were happening in their brains,” Lambert told me. “Our moms were better foragers, and bolder. And there were increased connections in neurons in the hippocampus. That’s involved in learning and memory, including spatial learning.” It’s what mothers need to become the efficient foragers that they are, more skillful than their virgin counterparts.

The research with the fathers showed much the same thing. Not only were the California mouse fathers behaving like the mothers, they were also experiencing the same kinds of changes in the brain. The control mice who weren’t fathers and hadn’t been exposed to pups didn’t show the same brain changes. The good dads had reduced neural activity in parts of the brain associated with stress, and increased activity in a couple of brain hormones—vasopressin and oxytocin. Interestingly, the researchers found that the foster dads showed some—but not all—of the brain changes seen in the biological fathers. Just being around pups, in other words, was enough to make a male’s brain partially resemble the brains of the good biological dads. It was similar to what Lambert had seen in her rodent mothers—being around pups produced changes in their behavior.

When they tried the same experiment with deer mice—the bad fathers—they found a much different picture. The dads and the foster dads were not distinguishable—both lacked many of the fathering-related brain changes seen in the California mice. These fathers have the circuitry and the neurochemistry to behave like good fathers. But they don’t exploit that circuitry to take care of their pups.

After the demonstration with the deer mouse and the California mouse, Franssen put the animals back in their proper cages. We gathered around a table in the lab, and I asked why there should be such a great difference between two species so closely related.

The hypothesis is that the difference arises from some critical features of the way the two species live. A father will stick around if his presence does something useful for his offspring. “If you can provide evidence that the offspring are healthier or better off when the father is there, then it’s adaptive for him to be there,” Lambert said. We’re all wired to pass on our genes, and males will do what they must to give their progeny the best chance of survival.

The California mice live in a desertlike strip of the state. It gets very hot during the day and very cold at night. The mothers leave their pups to forage at night, when it’s cold, so the fathers have to be there to keep the babies warm. It’s a reminder that studies of the brain ought to consider the brain in context. “It’s the same with humans,” Lambert explains. “Is the dad bringing something to the table? It doesn’t have to be money; it can be social interactions, intellectual strategies, or enriching life in some way.” If so, and it helps the children survive, it makes sense for the family to have evolved in such a way that the father hangs around.

If the father can’t do anything to boost his children’s prospects, he’s not going to stay around. That’s why, for example, vulnerable young turtles are left alone for the perilous crawl from nests on the beach into the sea. In this extreme case, neither mothers nor fathers can do anything to protect them. Lumbering awkwardly along the sand in their shells, they can’t groom their young or huddle to keep them warm the way the California mouse can. So the best strategy for turtles is to begin preparing immediately to have more offspring, rather than trying and failing to protect those they’ve already produced.

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Lambert and Franssen are not the only researchers looking to mice for answers to key questions about human males. Heidi S. Fisher and Hopi E. Hoekstra of Harvard University have been particularly interested in the
promiscuity
of deer mice. A female can mate with one male, and then another, and keep on going at a rate of more than one male per minute. How long the female can continue this sexual marathon isn’t clear. That’s because Fisher and Hoekstra didn’t follow the females. They followed the sperm. They found that the reproductive tracts of female deer mice were filled with sperm from multiple partners, but the sperm from each male could recognize their genetically related “siblings” as they swam upstream. “Brother” sperm from the same male tended to clump together, joining forces to try to penetrate the egg. The sperm best able to cooperate in this way boosted their chances of beating a competing male’s sperm to the egg. Fisher and Hoekstra found that deer mouse sperm have sickle-shaped heads topped with hooks that enable them to link up, forming tangled clumps with multiple wriggling tails. Other sperm were doing the same thing—hooking up with
their
kin—to make the competition that much keener.

The clincher came when the researchers looked at another closely related mouse, the oldfield mouse (
Peromyscus polionotus
, if you’re keeping score). This mouse is monogamous, and its sperm don’t have the ability to recognize and link to one another. But the monogamous mouse father doesn’t need that ability—there are no other sperm in the female’s reproductive tract, so it’s not a battleground for warring sperm from different sexual partners.

One of the most remarkable things Lambert sees in
her
mouse fathers is a conceptual leap from caring only for themselves to caring for someone else. “The mammalian leap to caring for others is something I’m fascinated by. You’ve extended your concern for survival to another being. Humans are right up there with [other] mammals that have a long childhood. Parenting is a long-term investment for humans. The more help you have, the more insurance you have. If nothing else, one parent could die. You have a backup.” And, importantly, each parent treats the children a little differently. “They’re complementing each other. This is great. It’s complex, and it’s interesting.”

*   *   *

Many animals have something to teach us about fatherhood—even those that are more distantly related to us than rats and mice, which should feel like cousins by now. Those animal species in which fathers do contribute to rearing the kids have found many different ways to carry out that mission. The one thing that they share, from seahorses to penguins to poison frogs, is that they all perform some essential function that helps their offspring survive. And by studying these essential contributions, we get some perspective on human fathering. Our way of doing things is not the only way.

One of the most famous animal fathers is the emperor penguin, whose epic fathering was featured in the Academy Award–winning documentary,
March of the Penguins
. When these monogamous penguins breed, fathers hold their partners’ eggs close to protect them from the unimaginably cold and black Antarctic winter. While fathers are guarding the eggs, the mothers march up to 100 miles to the ocean, where they eat their fill in preparation for feeding the hatchlings that will be waiting for them when they return to their partners. The fathers stand huddled together on sea ice in vast numbers for almost three months, trying to shield one another from knife-sharp winds and barely endurable temperatures. The fathers, lacking a nest to sit on, balance the single egg—each of which weighs up to a pound—on their feet, underneath a flap of feathered skin. There the eggs are kept at a temperature of about 95 degrees Fahrenheit—even when the temperature outside falls to 95 below zero.

One of the themes of
March of the Penguins
was the devotion between the parents. They make a serious contract with each other—the father trades protection of the egg for an abundant supply of baby food from the mother. For this to work, marital fidelity is required on the part of both parents, or the system would never have evolved as it did. But is the emperor penguin really monogamous? The film, ending with the joyful reunions of mother and father, leaves us wondering about what comes next.

The reality is that the reunions aren’t quite so joyful. When a mother returns from collecting food in the sea, she sings as she wanders through thousands of males, until she finds her mate. (If the mother is late in returning—most mothers return, incredibly, on the day their eggs hatch—the father regurgitates something called penguin milk, secreted by the lining of his esophagus, into the newborn’s beak.) The birds do a little dance, stand immobile for a few minutes, and then circle around each other, while the mother looks at the father’s flap of feathers, shielding the egg.

There the inspirational family story ends. According to the writer Jeffrey Moussaieff Masson, “The male allows the egg to fall gently to the ice, whereupon the female takes it and then turns her back to the male, to whom, after a final duet, she becomes completely indifferent.” The male “stares at his empty pouch, pecks at it with his beak, lifts up his head, groans, and then pecks the female. She shows no further interest in him and eventually he leaves for the open sea, to break his long fast. The whole affair has lasted about eighty minutes.” The following year, they mate again—but almost always with different partners.