Ever since Max the gorilla beat up a runaway thief in 1997, he has become everybody's hero in South Africa.

Five-year-old children regularly charge up to the star gorilla's enclosure when visiting Johannesburg zoo and now, Max is making headlines again because he refuses to mate with his girlfriend Lisa.

Seeing as southern Africa's total gorilla population comes to three, this is more than dramatic.

Scientists had even contemplated giving Max a dose of the virility drug viagra to help him get an erection but dropped the idea when the side-effects threatened to outweigh the benefits.

"Max and Lisa are like a bored elderly couple. There is no sparkle", says American animal reproduction expert Nadia Loskutoff. The nearly 30-year-old gorilla couple have been living together for ten years. Sparks fly only when a male peacock in the same enclosure comes too close to Max.

The main reason for Max's chastity seems to be Lisa's obesity. She trots around the enclosure scratching her big belly. Max on the other hand struts around majestically and rarely even glances in her direction. "Lisa is pretty fat and just does not feel sexy. But she has to become pregnant soon before it is too late", says Loskutoff.

Lisa exerts herself only when Max steals her food. She shows her distaste and disregards her boyfriend's feelings by nipping him. Understandably, Max just does not want to play the mating game. "Lisa would watch television all day, if she could", say experts from Henry Doorly zoo in Omaha, Nebraska.

Laziness, a lack of exercise and the fact that libido among gorillas wanes quickly, unlike other apes, does not help propagation. "Gorillas simply do not enjoy sex", says Loskutoff.

Nonetheless, Lisa is due to be artificially inseminated with sperm from a US zoo. "It will still be Max's child", the expert promises. He will not even notice that the child is not his own flesh and blood.

If the fertilisation planned for November is successful, Loskutoff plans to travel to South Africa with frozen embryos, one of which is for Lisa. Hopefully, that will lead to a big gorilla family. "We are convinced that there will soon be more that three gorillas in southern Africa - even if passion does not make a comeback", says Loskutoff. - Sapa-DP