A group seeking to quash provisions of the law that make it illegal for consensual same sex will call expert witnesses to support its case.
Appearing before a three-judge bench on Thursday, Senior Counsel Paul Muite said the group would call a psychiatrist to explain sexual orientation and why the State should not regulate intimate matters.
Mr Muite said the experts would table reports to demonstrate biological and social conditions that lead to a person's sexual orientation.
Mr Eric Gitari moved to court to decriminalise sections 162 and 165 of the Penal Code.
He said the parts were discriminatory and contravened provisions of the Constitution such as right to equality, freedom from discrimination, human dignity, freedom and security of the person and right to privacy.
ORDER OF NATURE
Section 162 reads: "Any person who has carnal knowledge ... against the order of nature; or has carnal knowledge of an animal; or permits a male to have carnal knowledge of him or her against the order of nature, is guilty of a felony and is liable to imprisonment for 14 years."
Section 165 says a man who commits any act of indecency with another man, or procures a man to commit indecency with him, or attempts to procure the commission of any such act with himself or with another male may be jailed for five years.
Mr Gitari said the petition had nothing to do with same sex marriage, did not seek its legislation and would not, if successful, have effect of mandating or requiring Kenya to recognise such a union.
Justices Roselyn Aburili, Chacha Mwita and John Mativo consolidated the case with a similar one filed by Mr John Mathenge and four others.
The Kenya Christian Professional Forum, through its lawyer Charles Kanjama, said it would also be calling two witnesses to give a divergent opinion. The forum said the penal code was within the confines of the law.
"The petition only concerns criminalisation and punishment of a section of society on account of the fundamental characteristic of sexual orientation," Mr Muite told the judges.
Mr Gitari, the director of National Gay and Lesbian Rights Commission in Kenya, an NGO which was established in April 2012, argued that criminalising conduct as unnatural and grossly indecent, were degrading.
The lawyer said he had been subjected to stigma and discrimination as a result of the provisions and risked being exposed to prosecution.
"The disputed provisions ... criminalise private consensual conduct between adults of the same sex. Furthermore, the provisions, by virtue of their vagueness and uncertainty, breach the principles or legality and the rule of law, infringing on the rights of citizens," read the petition.
He said the case was concerned with the constitutional legitimacy of the State seeking to regulate the most intimate and private sphere of Kenyans' conduct, regardless of their sexual orientation.
Sexual intimacy between consenting adults, he argued, was a fundamental part of the experience of humanity.
"It is an essential element of how individuals express love and closeness and how they establish and nurture relationships," he said.
Few aspects of an individual's life are more inherently private than the manner in which he or she experiences and expresses sexual intimacy with another person, the petition adds.
The case will be heard on February 22.