Is there a biological basis for the seven-year itch?

John Hopton for – Your Universe Online

Helen Fisher, a biological anthropologist at Rutgers University and author of Anatomy of Love: The Natural History of Monogamy, Adultery and Divorce, told Scientific American that for several years she has been investigating whether the “seven-year itch” (or the tendency to get divorced after seven years of marriage) really exists, and if there is a biological basis for it.

Fisher looked at nature and our evolutionary history and found that pairing for a certain length of time before separating is habitual. However, that length of time is not necessarily seven years.

“I began by studying worldwide data on marriage and divorce and noticed that although the median duration of marriage was seven years, of the couples who divorced, most did so around their fourth year together (the ‘mode’),” she explains. “I also found that divorce occurred most frequently among couples at the height of their reproductive and parenting years—for men, ages 25 to 29, and for women, ages 20 to 24 and 25 to 29—and among those with one dependent child.”

Only 25 percent of primate species are monogamous, and less than 5 percent of mammals form a monogamous bond to raise offspring. Fisher says that of all bird species a much higher 90 percent “team up” to raise young, but most only do so while the young are vulnerable. Once they are grown, the pair will break apart.

“The reason,” Fisher says, is that “the individual that sits on the eggs until they hatch will starve unless fed by a mate.” She explains that, “A few mammals are in the same predicament. Take the female fox: the vixen produces very thin milk and must feed her young almost constantly, so she relies on her partner to bring her food while she stays in the den to nurse.

“When juvenile robins fly away from the nest or maturing foxes leave the den for the last time, their parents part ways as well.”

Fisher says that humans retain traces of this reproductive pattern. In hunter-gatherer societies, women tended to have children around four years apart. Equally, it was around four years old that children moved on to raised by broader community groups more than the parents, who were free to find new partners if they chose to. The four-year divorce peak among modern humans may be an evolutionary hangover from this time.

According to Fisher, “Serial pair bonding may have been beneficial to survival among our forebears because having children with more than one partner produces offspring with greater genetic variety and a wider range of skills. Hence, in the changeable environment of ancient Africa, some offspring would have had a better chance of enduring.”

She adds that: “By understanding this susceptibility in our human nature, we might become better able to anticipate, and perhaps be able to avoid, the four-year itch.”

It is tempting and often useful to look to our ancestry and to nature for clues about our behavior, although those sources can also be ambiguous. Groups who oppose divorce celebrated the documentary movie March of the Penguins, because it showed monogamous pairs of penguins lovingly raising their young, and thought that nature was giving us a sign that we had let things slide, forgetting our natural obligations. However, if the movie had been called March of the Mallards, viewers would have seen ducks mating in what amounts to an orgy, involving males who rather than being faithful had a good chance of going on to perform necrophilia.

Within the complexity of human behavior, there must be more to our major decisions than just reproductive instinct. Humans are not necessarily consistent in any of their actions throughout a lifetime, and according to business site Fast Company “the median number of years a US worker has been in his or her current job is just 4.4.” Did hunter-gatherers become account manager-personal shoppers after four years?

Breaking up after four or seven years certainly seems to be partially biological, but at the same time “well foxes do it” probably won’t hold much sway with divorce courts.


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