Scotland's most senior Catholic has come under fire after claiming that proposals to allow gay couples to adopt would place children "in peril".
Cardinal Keith O'Brien urged Catholic families to adopt
Cardinal Keith O'Brien said youngsters would be guinea pigs in a "distorted social experiment".
He said studies had suggested that drug use, homosexuality, stress and mental illness were more common among those raised by same-sex couples.
But the cardinal was dismissed as being out of touch by gay rights activists.
Ben Summerskill, the chief executive of Stonewall, said: "We are saddened that a senior cleric is exhuming 19th Century prejudices rather than recognising the reality of life in the 21st Century.
"We're also saddened that he should be inciting prejudice against gay and lesbian people.
"There's no credible evidence to support the cardinal's view that the educational and social development of the children of gay and lesbian couples is any different from that of the mainstream population."
Green MSP Patrick Harvie, who also campaigns on gay rights, said Cardinal O'Brien was not willing to accept that same-sex relationships were as worthy as mixed-sex ones.
"I think it would be good if the cardinal caught up with the rest of society on this issue," he said.
The Scottish Executive said it would consider all the views it received during the consultation on the plans.
"We welcome the cardinal's views," said a spokesman. "Many people, however, will hold a different view."
The Catholic Church and the Church of Scotland have both spoken out against the proposals, which were unveiled in June.
People have until 31 October to have their say on the new legislation, which would allow unmarried and same-sex couples to adopt if they could prove that they were part of an enduring family relationship.
Writing in the Sunday Times, Cardinal O'Brien accepted that the current adoption system was failing children.
He urged Catholic families to come forward, predicting that if they did so there would be no need to widen the definition of those able to adopt.
He said the proposals were "gravely immoral" and would see children placed in an environment which was "not conducive to their full human development".
Cardinal O'Brien said one Spanish report had recorded a significant increase in low self-esteem, stress, confusion over sexual identity, increased mental illness, drug use, promiscuity, sexually transmitted infections and homosexual behaviour among children raised by same-sex couples.
"We ignore a wealth of global evidence and place innumerable children in peril if we forget certain immutable truths; children need a male and a female role model in a permanent relationship," he said.
"Scotland's adopted children must not become guinea pigs in some distorted social experiment aimed at redefining marriage, subverting the family and threatening the good of society."