Last week, the U.S. Supreme Court heard oral arguments in two
cases challenging legal restrictions on same-sex marriage.
Proponents and opponents sought to cudgel one another with
sociological and psychological studies aiming to prove that science
is on their side. Well, what does the science say?
Impact on Traditional Marriage
Some opponents told the court that same-sex marriage will
undermine conventional marriage among heterosexuals. So what do the
data say about how legalizing gay marriages affects conventional
marriages?
A 2009 study by University of Sherbrooke economist Mircea
Trandafir investigated the effect
of the legalization of same-sex marriage in the Netherlands,
the first country to recognize same-sex marriage. In 1998, the
Dutch created registered partnerships, which are open to all
couples, and in 2001 a law allowing full same-sex marriages. His
analysis found that same-sex marriage leads to a decline in the
different-sex marriage rate, but not in the different-sex union
(marriage plus registered partnership) rate. In other words, Dutch
heterosexual couples are taking advantage of the “marriage lite”
registered partnership alternative.
At the time of Prof. Trandafir’s study, the chief difference
between registered partnerships and marriage was that the former
could be dissolved at the civil registry by mutual agreement. In a
2012 West Virginia Law Review article, Mercer School of
Law professor Scott Titshaw shows that the political compromises
provoked by the initial
refusals to extend full marriage rights to same-sex couples
result in a proliferation of civil union alternatives. Prof.
Titshaw agrees with Prof. Trandafir that different-sex couples
increasingly find the new marriage alternatives attractive; in
effect, refusing to give full legal recognition to same-sex couples
ends up diminishing the status and benefits associated with
conventional marriage for everyone. Ironically, conservatives by
opposing the extension of full marriage rights to gay people have
ended up weakening the institution they sought to protect.
The Divorce Rate
Sweden legalized same-sex civil unions in 1995 and gay marriage
in 2009. A 2011 demographic study from researchers at the
University of Stockholm reports that since 1999, after decades of
falling, both the marriage rate and the
fertility rate have trended upward and the divorce rate is
down.
Massachusetts was the first state to legalize same-sex marriage
in 2004. In 2003, the divorce rate in Massachusetts was 2.5 per
1,000 residents, and it fell to 1.9 by 2009. The Massachusetts
marriage rate jumped 15 percent in 2004, as many same-sex couples
chose to get married, but since has remained stable. Interestingly,
the states that permit same-sex marriage tend to have lower divorce
rates than those that ban same-sex marriage.
A 2004 study of registered partnerships in Sweden reported that
gay male couples were 50 percent more likely to divorce than
were heterosexual couples. Lesbian couples were nearly three times
more likely to divorce than were heterosexual couples.
 But how salient are higher divorce rates among gays and
lesbians for making public policy? Consider that a 2008 study in
the journal Family Relations by Rice University
sociologist Jenifer Bratter found that in the U.S.
black-husband/white-wife marriages were
twice as likely to end in divorce as white/white couples, and
Asian-husband/white-wife couples were 59percent more likely. Yet
few would argue that interracial marriages should be prohibited
because their children are at substantially greater risk of
experiencing the social, psychological, and economic disadvantages
stemming from a higher interracial divorce rate.
Having Kids
Nearly 20 percent of
same-sex households—i.e., 115,000—reported having children, and
84 percent contained children biologically related to one of the
householders. In comparison, 94 percent of different-sex married
couple households with children reported living with their own
children. A study issued in February by the Williams Institute, a
gay public-policy think tank at the law school of the University of
California, Los Angeles, reports that 37 percent of “lesbian, gay,
bisexual and transgender” (LGBT) adults have had a child at some
time in their lives. In addition, the report notes that as many as
six million American children and adults have an LGBT
parent.
 Opponents and proponents of same-sex marriage spar
fiercely over the data about how children fare in same-sex
households. On March 21, when the American Academy of Pediatricians
issued a
statement in favor of same-sex civil marriage, the group also
published a technical report that comprehensively looked at the
available research on the well-being of children living in same-sex
households. The report noted that a big problem with current
research is the small sample sizes of many of the studies. An
additional problem is that most of the children in these studies
have been through divorce before living in a same-sex household.
Divorce is well known to have deleterious effects on the well-being
of children.
However, data are reassuring from the National Longitudinal
Lesbian Family Study, which includes 78 lesbian families who used
donor sperm to have children and have been followed since the
1980s. A 2012 study compared quality-of-life measurements of
adolescents from lesbian families with those from a matched set
of adolescents raised in different-sex homes. The researchers
reported that “adolescents reared by lesbian mothers from birth do
not manifest more adjustment difficulties (e.g., depression,
anxiety, and disruptive behaviors) than those reared by
heterosexual parents.”
 By the time that their children were age 17, some 55
percent of the lesbian couples had separated compared to 36 percent
of heterosexual couples in the National Survey of Family Growth.
However, children from separated lesbian couples don’t appear to
manifest the social and psychological problems often found among
children whose heterosexual parents are divorced. The better scores
achieved by the children of lesbians, the researchers point out
might result from the fact that 75 percent of the separated lesbian
couples shared custody, whereas 65 percent of divorced heterosexual
mothers had sole custody of their children.
 A 2010 study in the periodical Demography by
Stanford University sociologist Michael Rosenfeld parsed Census
data to compare the school progress of children
reared in same-sex, heterosexual, and single parent families.
He reported that “children raised by same-sex couples have no
fundamental deficits in making normal progress through school.”
Adoption Outcomes
A 2012 study by UCLA researchers involving 82 families (60
heterosexual, 15 gay, and 7 lesbian) who
adopted high-risk children from foster care found that on
average, children in both same-sex and different-sex households
“showed significant gains of approximately 10 IQ points in their
cognitive development and maintained stable levels of behavior
problems that were not clinically significant.”
The researchers noted that these findings were especially
remarkable because the children adopted by same-sex couples were
generally higher risk and often of a different ethnicity than those
adopted by heterosexual couples. The bottom line is that research
on the effects of being reared by same-sex parents on children is
certainly not perfect, but the AAP seems right when it concluded
that despite research “imperfections, it is likely that the
extensive research efforts that have been carried out would have
documented serious and significant damages if they existed.”
Monogamy
Research suggests one salient difference between same-sex,
especially gay male couples, and different-sex couples relates to
the acceptability of sex with people outside of the relationship. A
2010 study by University of Toronto sociologist Adam Isaiah Green
in the Canadian Journal of Sociology involving 30 same-sex married
couples around Toronto found that two-thirds of same-sex spouses
(40 percent female, 60 percent male) did
not believe marriage needed always to be monogamous. In fact,
nearly half of male same-sex spouses (47 percent) had an explicit
agreement that allowed for non-monogamy. In comparison, the
General Social
Survey reported in 2010 that
19 percent of men and 14 percent of women they had been
unfaithful at some point during their marriages.
My reading of the scientific literature as it currently stands
is that the legalization of same sex marriage does not have major
effects on marriage trends in the wider society. As ever greater
numbers of gay, lesbian, bisexual, and transgender Americans have
exited the closet, more straight Americans have come to know and
accept their homosexual family members, friends, and colleagues. It
is this personal data, not the dueling studies published in obscure
social science journals, that have now persuaded a majority of Americans
in recent polls to support same sex marriage.
A slightly different version of this article originally appeared
at the Wall Street Journal's Ideas Market.
Disclosure: My wife and I have supported Equality Virginia
for a number of years.
Earlier today I mentioned a new study by the
