Many people presume that children do better if they have a mother and a father - but a new study suggests otherwise.
Researchers are challenging the idea that children without a father are necessarily at a disadvantage.
Sociologist Timothy Biblarz, of the USC College of Letters, Arts and Sciences, says: "Significant policy decisions have been swayed by the misconception across party lines that children need both a mother and a father.
"Yet, there is almost no social science research to support this claim. One problem is that proponents of this view routinely ignore research on same-gender parents."
The article in the February issue of the Journal of Marriage and Family examines different studies on parenting.
Judith Stacey of NYU, who carried out the research with Biblarz, said: "That a child needs a male parent and a female parent is so taken for granted that people are uncritical."
The researchers found there was no evidence that mothers and fathers had different parenting abilities - apart from breastfeeding.
They wrote: "The social science research that is routinely cited does not actually speak to the questions of whether or not children need both a mother and a father at home.
"Instead proponents generally cite research that compares [heterosexual two-parent] families with single parents, thus conflating the number with the gender of parents."
They found that the actual gender of parents doesn't have much effect on children's psychological adjustment and social success.
There are far more similarities than differences among children of lesbian and heterosexual parents, according to the study.
Biblarz said: "The bottom line is that the science shows that children raised by two same-gender parents do as well on average as children raised by two different-gender parents.
"This is obviously inconsistent with the widespread claim that children must be raised by a mother and a father to do well."
Stacey added: "The family type that is best for children is one that has responsible, committed, stable parenting. Two parents are, on average, better than one, but one really good parent is better than two not-so-good ones.
"The gender of parents only matters in ways that don't matter."
What do you think? Does it matter whether parents are male or female?