In Tunisia these animals are often caught and exploited because of the tribal belief that they may increase male fertility.

But in California, where they received as much as 15 hours of daylight, the plants lost their male fertility.

On the next page, we'll take a look at what scientists have found out about vitamins and their impact on male fertility.

Alcohol did not affect male fertility, the researchers said.

Current data suggests a possible role of osteocalcin in male fertility.

A number of studies also suggest that male fertility may diminish with age.

The council has also pioneered research in male fertility, with the aim of developing a contraceptive for men.

Diet can also affect male fertility so eating well and avoiding alcohol applies to men, too.

By my estimate, in about 5,000 generations - 125,000 years - male fertility will be roughly 1 percent of what it is now.

Mutations in Y chromosomes are already known to reduce male fertility.