From an article in the Journal of Marriage and Family a few years ago:
How Does the Gender of Parents Matter? - Biblarz - 2010 - Journal of Marriage and Family - Wiley Online Library
Volume 72, Issue 1, pages 3–22, February 2010
"The entrenched conviction that children need both a mother and a father inflames culture wars over single motherhood, divorce, gay marriage, and gay parenting. Research to date, however, does not support this claim. Contrary to popular belief, studies have not shown that "compared to all other family forms, families headed by married, biological parents are best for children" (Popenoe, quoted in Center for Marriage and Family, p. 1).
Research has not identified any gender-exclusive parenting abilities (with the partial exception of lactation). Our analysis confirms an emerging consensus among prominent researchers of fathering and child development. The third edition of Lamb's (1997) authoritative anthology directly reversed the inaugural volume's premise when it concluded that "very little about the gender of the parent seems to be distinctly important" (p. 10). Likewise, in Fatherneed, Pruett (2000), a prominent advocate of involved fathering, confided, "I also now realize that most of the enduring parental skills are probably, in the end, not dependent on gender" (p. 18)."