A Cambridge University developmental psychologist testified at a federal trial in San Francisco today that broad research has documented that children of same-sex parents are just as likely as those of heterosexual parents to be well-adjusted.

"Studies have found children do not require both a male and female parent," testified Michael Lamb, who heads Cambridge's Department of Social and Developmental Psychology.

Lamb was called by lawyers for two same-sex couples who are challenging Proposition 8 as a violation of federal constitutional guarantees of equal protection and due process. Proposition 8, approved by 52.3% of voters in 2008, amended the California constitution to ban same-sex marriage.

He said childhood adjustment is determined by the relationships parents have with children and their relationships to each other.