The key mission of parents is to get their babies ready for the big world, for life beyond the (ideally) safe nursery of the nurturing home environment.
For the expectant field cricket, however, preparing her children for the world is a matter of life or death. In the cricket world, the wolf spider is a major nemesis. As its name implies, the spider lies in wait, recognizes motion, and attacks. The cricket who knows that spiders are around will move carefully, remaining hidden and motionless for long spans of time. But how does a young cricket know? Once it discovers that spiders are present—and dangerous—well, that information is too little, too late. So does the mother huddle up with her crickettes for a little maternity-ward tutorial?
Researchers in the United States recently investigated this question. They discovered that mother crickets pass the spider warning to their babies “in the womb,” so to speak. In the investigation’s clever yet somewhat chilling procedure, pregnant crickets were housed with a live spider whose mouthparts had been coated with wax; this rendered the spider nonlethal yet still scary. Sometimes the spider removed the wax and prematurely ended the experiment, but when the conditions remained as planned, the wary mother laid her eggs, and baby crickets were hatched and collected. Other pregnant crickets were housed in similar conditions but without the spider. Their offspring were also collected.
The researchers then exposed the two sets of babies to hungry spiders in various situations. Offspring of the spider-exposed mothers spent more time hiding and remaining immobile, and thus survived longer, than did the offspring of naïve mothers. “In total,” conclude the investigators, “our study provides the most comprehensive evidence to date for an adaptive transgenerational maternal effect on offspring antipredator behavior.”
What is the connection between this and human behavior? At first glance there seems to be little, but that’s because most of us are not usually involved in a predator-prey relationship. Of course, a sudden bump in the night reveals that we, too, have an innate freeze/can’t-see-me-if-I-don’t-move response to an unexpected event or sound. But there is a deeper and more important connection.
Clearly we also attempt to teach our young to observe the rules of society and culture, how to be safe and productive. As the Scriptures note, we should “train up a child in the way he should go” (Proverbs 22:6). But that teaching begins much earlier than many of us once suspected or acknowledged. Like the mother cricket, we preload our babies prenatally with valuable environmental cues and behavioral bias; we learn about the world before we are born. Human parental experience and behavior have a ripple effect across the generations.
This preprogramming can be either for the benefit or to the detriment of the next generation. The Scriptures also allude to this principle, as we will discover.
Nature and Nurture
The question of behavioral programming (“Why does our child do that?”) has piqued human curiosity from the beginning. At one point, before the discovery of cells, chromosomes and genes, the best hypothesis was preformation—the idea that the new child was already formed in miniature and simply grew larger to birth and then to adulthood. In this view the adult’s behavior and characteristics had been preset, predetermined from conception. As DNA and the other pieces of the genetics puzzle came together, it was initially easy to ascribe the same sort of presets to the new players. The genetic code became the new homunculus, the “little man” that ran the show.
It did not take long, however, to recognize that the little man was subject to other influences. If DNA alone were responsible for how we develop, then identical twins (called monozygotic because they develop from a single fertilized egg and therefore could be expected to have the same genetic makeup) should be exactly the same. Animal clones should likewise be the same. But experience shows that they are not; whether human, mouse or Dolly the sheep, twins are never truly identical.
Our collective immersion in more than a decade of post–Human Genome Project rhetoric concerning the dominant role of DNA has left us mostly oblivious of the idea that genes do not work in isolation. Genes must be controlled and managed; even if our DNA is the blueprint, it needs to be read and interpreted correctly.
In 1942 developmental biologist Conrad Waddington coined the term epigenetics to describe what were at the time unknown factors overriding the genes (epi- means “over” or “atop”). He and others postulated that there must be a system regulating gene expression. Variations in the turning on and off of genes would result in individualized characteristics in everything from cell differentiation to social behavior.
But while the label may highlight a possibility, it does not answer the question of how the system might actually operate. How do we, and our cells, know what to do? Is it nature, a genetic program that simply plays out in a predetermined way? Or is it somehow a matter of nurture, the result of unrecognized feedback links between the living system and its environment? Today we have terms like methylation and histone modification to describe the ways in which the genome is chemically marked, but we do not yet understand the full picture of how cells not only sense but record, retain and erase these cues. Recent research using bee colonies has linked these types of changes with the behavior of individual bees. Beyond that interesting finding, researchers also discovered that the epigenetic tags are transient, changing as bees move from job to job within the hive.
From the Darwinian viewpoint, natural variation among individuals is the key to survival. The environment selects which fit and which do not—a harsh sense of nurture at best. But the problem of how random variations can lead to something new and more effective has always been contentious. At one point Darwin suggested a system of adaptive variation that combined the action of the environment on the parent and the passing on of that experience to the next generation (see “Darwin’s Gemmules”). In his version of the inheritance of acquired characteristics, Darwin imagined a way to preprogram the next generation to fit the environment—in a sense, a way to direct evolution.
That directive role in the interplay between environment and genes is becoming a key area of study. Researchers Eva Jablonka and Marion J. Lamb have been pioneers in advancing this paradigm-shaking concept; although random mutation is not without consequence, they believe that organisms can integrate environmental and social cues epigenetically. Surprisingly, they suggest, Darwinian evolution shouldn’t be viewed as an entirely random process after all.
“The major differences stem from our focus on the origins of hereditary variations, some of which we maintain are semidirected, not entirely blind changes,” they write in Evolution in Four Dimensions. “It is this that leads to our claim that evolution has to be seen in terms of instructive, as well as selective, processes.”
Sins of the Fathers
Although the introduction of a nonrandom component to evolution is disruptive, the instructive nature of epigenetic programming appears indisputable. In The Epigenetics Revolution, virologist Nessa Carey explores many examples of epigenetics in action. In her chapter titled “The Sins of the Fathers,” Carey alludes to the Third Commandment’s warning regarding the transgenerational fallout of our choices and life events (“I, the Lord your God, am a jealous God, visiting the iniquity of the fathers upon the children to the third and fourth generations . . .” [Exodus 20:5]). To illustrate a possible epigenetic meaning to this warning, Carey discusses the Dutch Hunger Winter, which occurred when Germany set up blockades in 1944–45. “Some of the strongest evidence for transgenerational inheritance in humans comes from the survivors” of that ordeal, she writes, adding that because record-keeping was so good, not only the victims of the famine but also their children and their grandchildren could be monitored.
In referencing the commandment, however, Carey misses a greater point. In this case it is the refusal to acknowledge the sovereignty of the Creator that has both present and future costs: “. . . to the third and fourth generations of those who hate Me” (emphasis added). In other words, there are enduring consequences for choosing to live in ways opposed to God’s directions. “Visiting the iniquity of the fathers” indicates that there will be an accounting for one’s actions and for how one is taught to behave, not that the Creator must somehow personally and actively pursue every misdeed. We will each eventually give account to God as individuals (Ezekiel 18; Romans 14:11–12), but an abused and broken environment degrades us all if that is the world we have inherited from our ancestors or bequeath to our grandchildren.
There is ample reason to believe that the behavior of one generation affects the next. Recent primary research has been unequivocal in linking the pre- and postnatal environments with epigenetic programming and child health.
One investigator, biologist Michael K. Skinner, notes: “In contrast to the genetic control of cellular activity, the epigenetic cascade of events is responsive to environmental factors and can directly impact the genetic cascade of events.”
Psychologist Frances A. Champagne writes, “There is emerging evidence that changes in gene expression both within the brain and in peripheral tissues are associated with differences in the quality of the early environment and that these developmental effects are maintained by epigenetic mechanisms that control the activity of genes involved in disease risk and behavioral variation.”
A team of German investigators further found that household stress affected a baby’s stress programming: “This is the first demonstration that gestational exposure to psychological stressors can have a lasting impact” on the baby’s genetic expression. The researchers report that if a mother experiences IPV, or intimate partner violence, during pregnancy, the child will show it in the status of a particular gene during adolescence. They report, “As these sustained epigenetic modifications are established in utero, we consider this to be a plausible mechanism by which prenatal stress may program adult psychosocial function.”
Breaking the Chain
Evidence is growing to confirm that the impact of one generation on the next goes deeper than the imparting of social or cultural habits. The impact is also biological. While not genetic in the classic sense of changing one’s DNA code directly, the signs of what is now called “transgenerational epigenetic programming and inheritance” are being more clearly discerned and reported day by day. It’s not just about crickets. Our bodies and minds are molded by their interaction with the world as well as by the experience of our parents, passed down to us genetically, socially and epigenetically. There is much more to who we are and how we behave than the playback of our genetic sequence.
The dichotomy of nature versus nurture is slowly being resolved; in fact, some believe there is no separation at all: “As molecular biology uncovers more and more about epigenetic and genetic inheritance,” declare Jablonka and Lamb, “and as behavioral studies show how much information is passed on to others by nongenetic means, evolutionary biologists will have to abandon their present concept of heredity, which was fashioned in the early days of genetics, nearly a century ago.”
Rather than imagining that we are solely the result of nature—predetermined by our biologic inheritance (the heretofore mainly Darwinian, natural-selection view)—or of nurture (our environment), behavioral and cellular scientists are discovering that we are an intricately refined combination of both. The science of epigenetics is showing how our experience from conception to death affects the expression of our genes. This expression program not only controls the way our body is built, it also affects how we experience and respond to the world.
“When we hold our babies for the first time,” writes journalist Annie Murphy Paul, “we imagine them clean and new, unmarked by life, when in fact they have already been shaped by the world, and by us.” In reflecting on the nine months of her own pregnancy, she observes, “It’s a koan [or riddle] of parenthood, one worthy of long contemplation: We are meeting someone we know well for the very first time.”
Developmental psychologist David S. Moore adds, “Since ‘how we are’—human nature—can be understood from a developmental systems perspective to result from interactions between factors all of which we [as adults] can conceivably manipulate, we are ultimately responsible for our own nature.” This parallels the ancient edict to “choose life” (Deuteronomy 30:19–20) and participate in the benefits promised to those who change. No one need be trapped in the past; there is a reward that extends across the generations for those who willingly break away from the ways of life that separate humankind from the Creator (Exodus 20:6; Isaiah 59).
Our growing understanding of the epigenetic systems that orchestrate human growth and development shows that we are in many previously unrecognized ways “preprogrammed” at birth for certain behaviors or proclivities. But this programming is in flux. We can choose to change our thinking and behavioral patterns, and these changes appear to feed back into us in ways that can reprogram us and our future children biologically. From this perspective, we can be encouraged that the detrimental presets that can lead us astray in our relationships can be healed.
The idea of a form of inheritance operating outside our DNA code has been an unexpected revelation. But it should not come as a surprise; after all, if the Creator designed the cricket with a mechanism to protect its children, why would He not do the same for us?