NEW DELHI: Anti-gay rights groups, challenging legalisation of gay sex, were today asked by the Supreme Court to explain how such acts are against the order of nature as submitted by them.A bench of justices G S Singhvi and S J Mukhopadhaya said that the interpretation of constitution has changed over the last sixty years and the issue has to be seen in that light."What is homosexuality? Who is the expert to explain order of nature," the bench observed when the senior advocate Amrendra Saran submitted that nature does not recognise homosexuality and lesbianism which are against its order."Are surrogate mothers and test tube baby also against the order of the nature," the bench observed while asking Saran, appearing for Delhi Commission for Protection of Child Right , to explain it.The apex court was hearing petitions filed by anti-gay rights activists and also by political, social and religious organisations which have opposed the Delhi high court verdict decriminalising homosexual behaviour.The bench would continue hearing the case tomorrow.On February 7 last, the bench had refused to implead the armed forces in the case on the contentious issue.People and organisations from different fields have come out in support of or against the path-breaking verdict of the high court which had sparked a controversy.