Like the women two decades ago who decided to become mothers on their own — sparking a redefinition of family, not to mention a culture war — single men, gay and straight, hear the ticking biological clock. And they are moving beyond looking for Ms. or Mr. Right. Now, with fertility technology or adoption, the men are becoming single fathers. Last month, the singer Ricky Martin, 36, became the father of twins by surrogacy. Mr. Martin intends to be the sole parent, his publicist, John Reilly, said. Statistics on single fathers by choice are few, but there are indications that...