According to the Centers for Disease Control and Prevention, in 2005, there were 2,230,000 marriages, accounting for a marriage rate of 7.5 per 1,000 total population.  The 2005 divorce rate was estimated at 3.6 per 1,000 population.

"The propensity toward divorce does not lie mainly in the genes, new research suggests.

An Australian study of twins and their grown children finds that family history plays a key role, however. Adults whose own parents had split had nearly twice the risk of going through a divorce themselves, the researchers found.

But there is no "gene" for divorce, so to speak, said lead researcher Brian M. D'Onofrio, an Indiana University psychologist. "Genetic factors that influence both generations do not [significantly] account for that increased risk," he said.

The findings are published in the August issue of the Journal of Marriage and Family."

Criminologists have long believed that murder rates will climb when the number of young people grows, especially in areas where unemployment runs high and urban populations are growing.  However, a new study by Rutgers sociologist Julie A. Phillips suggests that the homicide rate may track less closely than previously thought with the size of population centers or with the number or employment status of the young people.  But one all-too-certain portent of murder remains: namely, divorce.

Examining county-by-county data collected between 1970 and 1999, Phillips uncovers a pattern that contradicts rather than confirms conventional wisdom among criminologists. In analyses that she calls "intriguing," Phillips shows that the statistical relationships between homicide rates on the one hand and unemployment and population size on the other are both negative, so manifesting "effects that run contrary to common theoretical expectations."  

As most criminologists would expect, Phillips does discern "a positive association between the proportion [of] young [in various areas] and homicide rates within U.S. counties across time."  But Phillips's multi-variable analysis establishes that "criminogenic forces, such as poor social conditions..., can alter the association between the relative size of the young population and homicide rates."  

One particular social measure especially helps Phillips recognize areas with the kind of  "low social control" that looses murderous impulses, even if those impulses are "less heavily concentrated in the young age ranges" in the affected areas than some theorists might have expected.  The indicator of social breakdown that Phillips highlights as a predictor of murder is the divorce rate.  

Unlike elevated unemployment rates and burgeoning population size-both surprisingly linked to lower homicide rates-high divorce rates do augur bloodshed.  In four out of five of Phillips's statistical models, the county divorce rate emerges as a statistically significant predictor of the homicide rate (p < 0.05 in all four models).  "On average," Phillips accordingly observes, "higher levels of the percentage of the population divorced are associated with larger homicide rates within counties over time."  

County coroners, it appears, will often be called on for grim duties wherever the divorce courts are busy.